Impactor with automatic energy control

Abstract

A surgical impactor 100 comprising an anvil, a striker 180, a driving mechanism 190 and one or more sensors to detect displacement of the anvil during impact and / or vibration of the surgical impactor

Description

TECHNICAL FIELD The present disclosure relates to surgical impactors. In particular, but without limitation, this disclosure relates to surgical impactors that are configured to monitor sensor data during operation and adapt operating parameters to improve performance. BACKGROUND When performing surgery, particularly hip replacement surgery, it is sometimes necessary to provide an impact force. This can be through the use of a surgical mallet and hip hammer. For instance, in total hip replacement surgery, a surgeon may utilise a broaching tool to remove less dense (cancellous) bone from a femoral canal without damaging the hard cortical bone surrounding it. This broaching may require multiple strikes, both in the forward and reverse direction. Thereafter, the surgeon may seat an implant in the prebroached femur and seat a head on the implant. Similarly, when seating an acetabular cup, the acetabular may be reamed using a reamer before an acetabular cup is inserted. The acetabular cup may be held in place by a press-fit. Seating the acetabular cup may require a number of impactions (e.g. 8-10 impactions) to ensure a secure fit. The use of manual techniques including those involving surgical mallets and hip hammers are limited in scope and / or consistency. For instance, it can be difficult for a surgeon to control direction, extent and force of impact. In addition, the repetitive force required by manual techniques can tire the surgeon and can result in injury over time. SUMMARY OF INVENTION The present disclosure relates to surgical impactors, and in particular, to impactors configured to monitor sensor data during operation and adapt operating parameters to improve performance. For instance, the force, displacement, direction and / or frequency of impacts may be adjusted based on sensor data representing one or both of vibration of the surgical impactor and / or anvil displacement. It has been observed that implant (e.g. acetabular cup) fixation strength is maximum at the point where the implant is unable to progress any further. Further impactions beyond this point can cause the fixation strength to decrease and / or can cause damage to the patient. Identifying this point of maximum fixation strength is difficult with existing conventional and powered impactors. By adapting operating parameters based on sensor data, certain embodiments are able to reduce the risk of bone fracture whilst improving the effectiveness of seating implants. In addition, certain embodiments are able to improve the comfort levels experienced by surgeons and reduce the risk of work-related injuries to surgeons by providing an alert and / or performing remedial action (e.g. stopping operation) in response to detecting vibration levels that are higher than a threshold. Similarly, impacts that have less than a minimum anvil displacement can cause excessive energy to be transferred to the patient, which could injure the patient. An alert can be issued and / or remedial action can be taken in response to the anvil displacement dropping below a minimum anvil displacement. Furthermore, particular embodiments are able to accurately measure bone quality (e.g. bone density) by measuring anvil displacement. This measure of bone quality can then be used to adapt operating parameters (e.g. impact force) to ensure that the impacts are tailored to the mechanical characteristics of the bone being impacted. According to a first aspect there is provided a computer-implemented method for controlling a surgical impactor. The method comprises: controlling the surgical impactor to drive a striker to deliver, via an anvil, one or more impacts at a first impact force; obtaining sensor data representing displacement of the anvil during each of the one or more impacts; and in response to determining the displacement of the anvil upon impact does not meet a displacement condition, adjusting one or more operating parameters of the surgical impactor to adjust the impact force applied by the surgical impactor. The adjusting comprises: in response to determining the displacement of the anvil upon impact is less than a lower threshold for anvil displacement, increasing the impact force; or in response to determining the displacement of the anvil upon impact is greater than an upper threshold for anvil displacement, decreasing the impact force. The displacement condition may be a displacement range (e.g. between the lower threshold and the upper threshold). Accordingly, determining whether the displacement of the anvil upon impact does not meet a displacement condition may comprise determining whether the displacement of the anvil is greater than or equal to the lower threshold and / or is less than or equal to the upper threshold). In certain embodiments, a first maximum impact force is set, and the adjusting does not allow the impact force to be increased beyond the first maximum impact force. In one embodiment, the method comprises: controlling the surgical impactor to drive the striker to deliver, via the anvil, one or more further impacts at the adjusted impact force; obtaining additional sensor data representing displacement of the anvil during each of the one or more further impacts; and in response to determining the displacement of the anvil upon impact during the one or more further impacts is less than a minimum anvil displacement, further adjusting the one or more operating parameters of the surgical impactor to increase the impact force to a second impact force. The second impact force is greater than the first maximum impact force. In one embodiment, the method comprises: controlling the surgical impactor to drive the striker to deliver, via the anvil, one or more further impacts at the further adjusted impact force. The further adjusting may comprise increasing the maximum impact force to a second maximum impact force. The further adjusting may not allow the impact force to be increased beyond the second maximum impact force. In one embodiment, the first impact force and the second impact force are in the same direction. In one embodiment, the further adjusting comprises reducing an impact frequency. In one embodiment, prior to the further adjusting, the operating parameter set defines a reciprocating mode to drive the striker to alternately deliver impacts in a first direction and a second direction. The first direction is opposite to the second direction, and the one or more impacts at the first impact force are delivered in the first direction. After the further adjusting, the operating parameter set defines a unidirectional mode to provide one or more impacts at the second impact force in the first direction. In one embodiment, the operating parameter set defines a unidirectional mode to provide impacts in a first direction. In one embodiment, one or more of the first impact force, the second impact force, the first maximum impact force and the second maximum impact force are determined based on a measure of the bone quality of bone being impacted. According to an embodiment, the method comprises: controlling the surgical impactor to drive the striker to deliver, via the anvil, one or more impacts having a predetermined impact force; obtaining sensor data representing displacement of the anvil during the one or more impacts having the predetermined impact force; and determining the measure of the bone quality of the patient based on the displacement of the anvil during the one or more impacts having the predetermined impact force. According to an embodiment, the method comprises: obtaining sensor data representing vibration of one or more portions of the surgical impactor during each of the one or more impacts; in response to determining that the vibration of the one or more portions of the surgical impactor is greater than a maximum vibration threshold, performing one or more of the following actions: controlling the surgical impactor to stop, or reduce an impact force of, one or more future impacts by the surgical impactor; and issuing an alert. The one or more impacts may be in a first direction (e.g. forward direction) or a second direction (e.g. reverse direction). According to another aspect there is provided a computer-implemented method for controlling a surgical impactor. The method comprises: controlling the surgical impactor to drive a striker to deliver, via an anvil, one or more impacts at a first impact force in a first direction according to a first operating parameter set; obtaining sensor data representing one or both of displacement of the anvil during impact and vibration of one or more portions of the surgical impactor during impact; in response to determining that the vibration of the one or more portions of the surgical impactor is greater than a maximum vibration threshold and / or the displacement of the anvil during impact is less than a minimum anvil displacement threshold, performing one or more of the following actions: controlling the surgical impactor to stop driving the striker in the first direction, controlling the surgical impactor to reduce an impact force of one or more future impacts by the surgical impactor and issuing an alert In one embodiment, controlling the surgical impactor to reduce the impact force of one or more future impacts by the surgical impactor reduces the impact force in the first direction. The first direction may be a forward direction or a backward (e.g. reverse) direction. In one embodiment, controlling the surgical impactor to drive the striker to deliver, via an anvil, one or more impacts at a first impact force in a first direction also comprises controlling the striker to drive the striker to deliver one or more impacts in a second direction (e.g. alternating with impacts in the first direction). In one embodiment, controlling the surgical impactor to stop driving the striker in the first direction comprises controlling the surgical impactor to completely stop driving the striker (e.g. to stop any further impacts, regardless of direction), or controlling the surgical impact to stop impacts only in the first direction (e.g. starting or continuing impact(s) in the second direction). In one embodiment, controlling the surgical impactor to reduce an impact force of one or more future impacts comprises: controlling the surgical impactor to drive the striker according to a second operating parameter set to perform one or both of the following actions: deliver one or more impacts in the first direction at a second impact force that is less than the first impact force; and provide one or more impacts in a second direction, opposite to the first direction. In one embodiment, the first operating parameter set defines a first impact frequency and the one or more impacts in the second direction are at a second impact frequency that is less than the first impact frequency. In one embodiment, the one or more impacts in the second direction are at a third impact force that is greater the first impact force. In one embodiment, the one or more impacts comprise a plurality of impacts and the direction of the plurality of impacts alternates between a first direction and a second direction opposite to the first direction. The method comprises, in response to determining that the vibration of the one or more portions of the surgical impactor is greater than the maximum vibration threshold and / or the displacement of the anvil during impact in the first direction is less than the minimum anvil displacement threshold, controlling the surgical impactor to reduce an impact force of one or more future impacts by the surgical impactor in the first direction or stop future impacts by the surgical impactor in the first direction. In this embodiment, one or more impacts may be continued in the second direction (e.g. the method may switch from reciprocal mode to reverse mode). In one embodiment, controlling the surgical impactor to drive the striker to deliver, via the anvil, one or more impacts in the first direction also comprises controlling the surgical impactor to drive the striker to deliver, via the anvil, one or more impacts in the second direction, and the method comprises in response to determining that the vibration of the one or more portions of the surgical impactor is greater than the maximum vibration threshold and / or the displacement of the anvil during impact is less than the minimum anvil displacement threshold, controlling the surgical impactor to reduce an impact force of one or more future impacts by the surgical impactor in the second direction. In one embodiment the method comprises, in response to determining that the displacement of the anvil during impact is less than the minimum anvil displacement threshold, controlling the surgical impactor to: stop driving the striker in the first direction or reduce an impact force in the first direction; and begin impacting in a second direction opposite to the first direction or increase an impact force in the second direction In one embodiment, the alert is issued to one or both of an external device or an output device of the surgical impactor. According to another aspect there is provided a computer-implemented method for controlling a surgical impactor, the method comprising: controlling the surgical impactor to drive a striker to deliver, via an anvil, one or more impacts having a predetermined impact force; obtaining sensor data representing displacement of the anvil during impact; and determining a measure of bone quality based on the displacement of the anvil during impact. In one embodiment, the method further comprises adjusting one or more operating parameters of the surgical impactor that control the driving of the striker based on the determined measure of bone quality. In one embodiment, the adjusting comprises setting one or more of: an impact force for one or more future impacts, and a maximum impact force. The impact force may be set to be lower for lower bone quality and higher for higher bone quality. The maximum impact force may set a force limit for one or more future impacts. The maximum impact force may be set to be lower for lower bone density and higher for higher bone density. In one embodiment, the measure of bone quality is determined based on a mapping of bone quality to anvil displacement for the predetermined impact force. In one embodiment, the mapping is dependent on one or more patient characteristics. According to another aspect there is provided a computer-implemented method for controlling a surgical impactor, the method comprising: determining an amount of force applied to the surgical impactor to push the surgical impactor against an object or pull the surgical impactor away from an object; adjusting a driving force applied by a motor of the surgical impactor to drive a striker to impact an anvil based on the amount of force. A higher driving force is set for a higher amount of force than for a lower amount of force. In one embodiment, the amount of force is determined based on a position of the anvil within the surgical impactor. The anvil is moved backwards within the surgical impactor in response to the surgical impactor being pushed against the object, and is moved forwards in response to the surgical impactor being pulled away from the object In one embodiment, an increased reverse driving force is applied in response to an increased pulling force being applied to the surgical impactor and / or an increased forward driving force is applied in response to an increased pushing force being applied to the surgical impactor. In one embodiment, the driving force is provided by the driving mechanism through adjusting the current passing through each electromagnet to provide a moving magnetic field. The force provided by the driving mechanism may be controlled by adjusting the magnitude and rate of change of the currents. The driving force applied to accelerate the striker may control the velocity of the striker, thereby controlling the energy and / or force of impact. According to another aspect there is provided a surgical impactor comprising: a striker; an anvil; a driving mechanism configured to drive the striker to impact the anvil; one or more sensors configured to measure one or both of: displacement of the anvil during impact; and vibration of one or more portions of the surgical impactor during impact; and a processor configured to implement any of the methods described herein (e.g. summarised above). In one embodiment, the surgical impactor comprises an attachment coupling connected to the anvil and configured to couple to an attachment for delivering one or more impacts. In one embodiment, the surgical impactor comprises a bone quality tester for measuring the bone quality, the bone quality tester being connected to the anvil to transfer one or more impacts to impact a bone being tested. In one embodiment, the bone quality tester is removably attached to the anvil. In one embodiment, the surgical impactor comprises a rest extending along at least one side of the bone quality tester and configured to contact the bone being tested at one or more contact points to provide support for the surgical impactor during impact In one embodiment, the rest is removably attached to the surgical impactor In one embodiment, there is provided a processor for controlling a surgical impactor to implement any of the methods described herein (e.g. summarised above). In one embodiment, there is provided a computer readable medium comprising computer executable instructions that, when executed by a processor, cause the processor to perform any of the methods described herein (e.g. summarised above). BRIEF DISCRIPTION OF THE DRAWINGS Arrangements of the present invention will be understood and appreciated more fully from the following detailed description, made by way of example only and taken in conjunction with drawings in which: Figure 1A shows a surgical impactor fitted with a broaching tool according to an embodiment; Figure 1B shows a surgical impactor fitted with an acetabular cup implant according to an embodiment; Figure 2 shows a cross section of a surgical impactor according to an embodiment. Figure 3 shows an enlarged view of region A of Figure 2; Figure 4 shows an enlarged view of region B of Figure 2; Figure 5 shows a plot of velocity over time for the anvil and striker during acceleration and impact; Figure 6 shows a plot of anvil displacement and impact energy for a series of impacts; Figure 7 shows a method for adjusting impact force based on anvil displacement according to an embodiment; Figure 8 shows a method for adjusting maximum impact force based on one or both of anvil displacement and vibration according to an embodiment; Figure 9 shows a method for preventing injury to a patient or surgeon during use of an impactor according to an embodiment; Figure 10 shows a surgical impactor including a bone quality tester according to an embodiment; Figure 11 shows a method for determining a measure of bone quality using a surgical impactor according to an embodiment; Figure 12 shows a block diagram of a control system for controlling a surgical impactor according to an embodiment; DETAILED DESCRIPTION To allow more precise control of impacts, and to reduce the surgeon’s strain and risk of injury, a surgical impactor may be used to electrically or pneumatically provide an impact force. This application relates to surgical impactors capable of automatically adjusting one or more operating parameters and / or operating modes based on sensed parameters, such as impact displacement, impact vibration, impact force or impact energy. For instance, particular embodiments monitor anvil displacement during impact and in response to the displacement being less than a threshold displacement, increase the impact force. This allows lower force(s) to be used for initial impacts to reduce the risk of bone fracture, and then higher force(s) can be used to finally seat an implant upon detection that the implant is nearly fully seated. The range of forces categorised as lower forces or higher forces may vary depending on the total or maximum energy levels required to fully seat implants. These forces may depend on the particular characteristics of the patient (e.g. age, bone density, etc.). Accordingly, one or more patient characteristics may be input into the system for determining the force(s) for one or more impacts. Further embodiments monitor vibration of the impactor and / or anvil displacement during impact(s) and, in response to detecting that the vibration is greater than a maximum vibration and / or anvil displacement is less than a minimum displacement, control the impactor to: stop, or reduce an impact force of, impacts in a first (e.g. forward or reverse direction); and / or issue an alert. A high vibration level may indicate that the impactor has supplied too much force / energy to the accessory, such that the anvil has progressed to the end of its travel, and the surplus kinetic energy of the striker is transferred to the impactor and ultimately to the surgeon resulting in increased Hand Arm Vibration (HAV) levels. This can be detected through monitoring vibration of the impactor. On the other hand, a low anvil displacement level may indicate that the broaching tool may also become lodged within the patient, which can cause excess energy to be transferred to the patient. This can damage the bone (e.g. increase the risk of bone fracture). Accordingly, in response to detecting vibration above a maximum vibration threshold and / or anvil displacement below a minimum displacement, the impactor may be controlled to stop, reduce its impact force in the first (e.g. forward) direction, and / or reduce its impact force in ora second (e.g. reverse) direction; or apply a force in a second (e.g. reverse) direction to dislodge the broach tool. In addition, or alternatively, an alert or warning may be issued to inform the user. This helps to avoid the risk of injury to the patient or surgeon, for example, where the impactor has become lodged within the bone of a patient. Further embodiments determine a measure of bone quality (e.g. bone density) based on measuring impact displacement for a given impact force. This allows the impactor to adjust its operating parameters (e.g. impact force or maximum impact force) based on bone quality to improve performance and reduce the risk of bone fracture. For instance, impact force may be reduced for lower bone quality and impact force may be increased for higher bone quality. Figure 1A shows a surgical impactor 100 fitted with a broaching tool 150 according to an embodiment. Figure 1B shows a surgical impactor 100 fitted with an acetabular cup 160 according to an embodiment. The surgical impactor 100 comprises a handle 110, a body 120 and an attachment coupling 130. The body 120 and handle 110 may collectively form a housing for the surgical impactor 100. The body 120 houses an anvil 170, a striker 180 and a driving mechanism 190 (see Figure 2). The driving mechanism 190 is configured to drive the striker 180 to impact the anvil 170. The anvil 170 is connected to the attachment coupling 130 such that impact force is transmitted from the anvil 170 to the attachment coupling 130. The attachment coupling 130 is configured to receive and secure an attachment. For instance, as shown in FIG. 1A, a broaching tool 150 may be attached to an adaptor 155 which may be received and secured within the attachment coupling 130. Similarly, as shown in FIG. 1B, an acetabular cup 160 may be attached to an adaptor 165 which may be received and secured within the attachment coupling 130. When the anvil 170 is impacted, the impact force is transmitted to the attachment via the attachment coupling 130. The attachment is therefore driven to provide an impact force (e.g. to bone). The broaching tool 150 comprises an elongate body having teeth. The teeth may be in the form of ridges running around the circumference of the elongate body. The broaching tool 150 may be mounted onto an adaptor 155 which may be secured within the attachment coupling 130. The broaching tool 150 may be used for broaching (e.g. broaching a femoral canal). When driven to reciprocate forwards and backwards, the teeth cut into the cavity being broached (e.g. into the bone) and then pull loose material out of the cavity being broached. Alternately broaches may be configured to compact the soft cancellous bone, in which case these tend to be driven predominantly in the forward direction. The acetabular cup 160 comprises an external curved (e.g. hemi-spherical) surface. The external curved surface may be convex. The external curved surface may be roughened. A socket on an opposite side to the curved external surface may be configured to receive a femoral implant consisting of a stem and a head. The acetabular cup 160 may be mounted to an adaptor 165 which may be secured in the attachment coupling 130. The acetabular cup 160 may be seated within an acetabulum through repeated impacts, driven by the impactor 100. After seating, the adaptor 165 is removed from the acetabular cup 160 to allow the femoral implant to be fitted within the acetabular cup 160. As noted above, the impactor 100 may also be fitted with various adaptors. The adaptors may act as a means of mounting different attachments (e.g. broaches, acetabular cups, etc.) to the impactor 100. Different adaptors may be used depending on the surgical approach and type of attachment being connected to it. They can also be used on their own (connected to the attachment coupling 130) for impacting other components (e.g. the femoral implant, femoral head, acetabular liner, etc.) and for revision surgery. The surgical impactor 100 may be provided with one or more of a trigger 140, a mode selector 145, and a power selector 147. The trigger 140, mode selector 145 and power selector 147 are all input devices, allowing the user to adjust operating parameters, instruct the device to operate and change operating mode. The operation of the surgical impactor may be controlled by a processor (not shown). The trigger 140 is configured to, in response to being depressed, provides an input to a processor to instruct the surgical impactor to drive the striker 180 to impact the anvil 170. The trigger 140 may be configured to output a varying signal depending on the extent that the trigger is depressed. The processor may be configured to adjust the impact force and / or impact frequency based on the extent that the trigger 140 is depressed (e.g. increase impact force and / or impact frequency with greater depression and decrease impact force and / or impact frequency with lesser depression). The mode selector 145 may be configured to input a mode signal to the processor. The mode signal may define an operating mode of the impactor 100. The mode may be selected from forward mode, backward mode, and reciprocating mode. In one embodiment, the mode selector 145 is a sliding switch, with different positions of the sliding switch defining different modes. For instance, a forward position may define forward mode, a middle position may define reciprocating mode, and a backward position may define reverse mode. In forward mode, the striker 180 may be driven to impart a primary force in a first direction (defined herein as a forward direction). The forward direction may be a direction in which the attachment coupling 130 (and by extension, an attachment or adaptor secured in the attachment coupling 130) moves away from the body 120 (e.g. along a longitudinal axis of the body 120). In reverse mode the striker 180 may be driven to impact a primary force in a second direction opposite to the first direction (defined herein as a reverse direction). The reverse direction may be a direction in which the attachment coupling 130 (and by extension, an attachment or adaptor secured in the attachment coupling 130) moves towards the body 120 (e.g. along the longitudinal axis of the body 120). In reciprocating mode, the striker 180 is driven to alternately drive the striker 180 in the forward direction and in the reverse direction to alternately impact the anvil 170 to impart a first primary force in the forward direction and to impact the anvil 170 to impart a second primary force in the reverse direction. Whilst the forward and reverse modes of operation drive the striker 180 to impart primary forces in the forward and reverse directions respectively, they also may drive the striker 180 to move opposite to these directions (e.g. to prepare to be driven). When preparing to be driven, the striker 180 may impart a secondary force to the anvil 170 in an opposite direction to the primary force in that mode of operation. This secondary force may be smaller (e.g. may have a smaller magnitude) than the primary force. The power selector 147 may be configured to input a power signal to the processor to control an impact force or energy. In the present description, the terms “power”, “force” and “energy” may be used interchangeably when discussing the force of impact. It will be appreciated that these terms are related to each other, such that a larger impact force will impart a larger amount of kinetic energy and that, more powerful impacts (e.g. through driving the striker 180 more powerfully) will impart more force. The power selector 147 may be in the form of a rotating dial, although alternative forms of input device may be used. The power selector 147 may have varying positions related to specific power modes. For instance, one or more power modes may relate to respective levels of impact force. A safety mode may stop the impactor 100 from being driven (e.g. by disabling the driving of the impactor 100 and / or locking the trigger 147). An automatic mode may allow the operating parameters (e.g. impact force) to be adjusted automatically by the processor. The automatic mode may allow the operating parameters to be adjusted by an external device. Figure 2 shows a cross section of a surgical impactor 100 according to an embodiment. The surgical impactor 100 comprises an anvil 170, a striker 180 and a driving mechanism 190. The anvil 170 (otherwise known as an anvil system) includes a front anvil 172, a rear anvil 174 and a connector 176. The front anvil 170 is connected to (e.g. integrated with) the attachment coupling 130, such that movement of the anvil 170 causes the attachment coupling 130 (otherwise known as a tool holder) to also move. Any attachment or adaptor held within the attachment coupling 130 is therefore driven. For instance, a broaching tool or acetabular cup may be driven via a corresponding adaptor secured within the attachment coupling 130. The front anvil 172 and the rear anvil 174 are positioned on either side of the striker 180. The connector 176 connects the front anvil 172 to the rear anvil 174 such that the anvil 170 forms a single unit. In the present embodiment, the connector 176 is in the form of a shaft that runs along a longitudinal axis of the impactor 100. The striker 180 is mounted within the body 120 such that it may slide forwards and backwards within a cavity within the body 120, between the front anvil 172 and the rear anvil 174. The striker 180 may include bearings (e.g. linear bearings) which are configured to assist the striker 180 in moving longitudinally. The bearings may act on an internal wall within the impactor 100. The internal wall may define a longitudinal cavity within which the striker 180 is housed. The longitudinal cavity may be cylindrical. In one embodiment, the striker 180 is configured to move along the connector 176. For instance, a shaft may pass through the striker through which the connector 176 passes. For instance, the shaft may be centrally located (e.g. along a central longitudinal axis of the striker 180). The striker 180 may be cylindrical. Having said this, alternative arrangements are possible, which have a variety of different shapes of striker 180. Similarly, alternative arrangements are possible which may have a different shaped connectors 176 and / or different numbers of connectors 174. The striker 180 is configured to be driven by the driving mechanism 190 to impact the anvil 170 to impart a force to the coupling attachment 130. The driving mechanism 190 may be pneumatic or electromagnetic. In the remaining description, it shall be assumed that the driving mechanism is electromagnetic. The driving mechanism 190 may comprise a motor (for instance, an electromagnetic motor). For instance, the driving mechanism 190 may be a linear electromagnetic motor. The striker 180 may include magnets 182 (referred to herein as “striker magnets”) configured to be driven by the driving mechanism 190. The striker magnets 182 may be annular (ring shaped). The magnets 182 may be magnetised along a direction parallel to the longitudinal axis of the impactor 10 (e.g. parallel to the direction of movement of the striker 180). The driving mechanism 190 may comprise a number of electromagnets. By alternating the polarity, the strength of the magnetic field generated by the magnets 182 is increased. The driving mechanism 190 may be a rectilinear motor configured to drive the striker 180 forwards and rearwards along the longitudinal axis. A driving force may be provided by the driving mechanism 190 through adjusting the current passing through each electromagnet to provide a moving magnetic field. The force provided by the driving mechanism 190 may be controlled by adjusting the magnitude and rate of change of the currents. Processing circuitry (not shown) is configured to control the driving mechanism 190. The processing circuitry is configured to control the driving mechanism 190 to drive the striker 180 in response to an input from the user through the trigger 140. The operation of the processing circuitry shall be described in more detail later. When the striker 180 is driven in a forward direction, it impacts the front anvil 172 and imparts a force in the forward direction. When the striker 180 is driven in a reverse direction, it impacts the rear anvil 174 and imparts a force in the reverse direction. The forward and reverse directions are opposite to each other and are both parallel to the longitudinal axis. The terms “forward”, “reverse”, “backward” and “rearward” are intended to be relative terms (i.e. relative to the structure of the impactor 100) and are not intended to relate to any orientation of the impactor 100 in use. A centring system may be provided to provide biasing forces to centre the anvil 170 after it has been displaced. The centring system may comprise a number of resilient members (e.g. springs, dampers, etc.). The centring system may be configured to bias the anvil system 170 towards a resting position. For instance, after the anvil system 170 has been driven forward within the body 120, the centring system may be configured to bias the anvil system 170 rearwards, towards the resting position of the anvil system 170. Similarly, after the anvil system 170 has been driven backwards within the body 120, the centring system may be configured to bias the anvil system 170 forwards, towards the resting position of the anvil system. The driving mechanism 190 can be controlled to drive the striker 180 to provide a single impact, or a sequence of impacts. Once the user engages the trigger 140, the striker 180 is driven to impact the anvil 170. If the user continues to engage (hold down) the trigger 140, then the processing circuitry controls the driving mechanism 190 to reciprocate the striker 180 to provide a continuous sequence of impacts. At the point that the user releases the trigger 140, then the driving mechanism 190 disengages and the striker 180 is returned to a resting position. The processing circuitry is configured to control the driving mechanism 190 according to one of three selectable modes of operation: forward mode, reverse mode, and reciprocating mode. The processing circuitry is configured to switch between these modes of operation based on an input from the user through the mode selector 145. In forward mode, the impactor 100 is configured to provide a primary force in the forward direction. In reverse mode, the impactor 100 is configured to provide a primary force in the rearward direction. In reciprocating mode, the impactor 100 is configured to alternately provide forward and backward primary forces. The strength of the primary force(s) imparted by the impactor 100 can be set through input from the user via the power selector 147. When driven (e.g. in response to an input via the trigger 140), the driving mechanism 190 may initiate the striker 180 by moving the striker 180 to an initiation position. In forward mode, the initiation position may be rearward of the resting position of the striker 180. In reverse mode, the initiation position may be forwards of the resting position of the striker 180. In reciprocating mode, the initiation position may depend on whether the first primary impact is to be a forward or rearward impact. In certain embodiments, the first primary impact in reciprocating mode is a forward impact. Positioning the striker 180 at the initiation position provides the striker 180 with an increased distance over which it can be accelerated towards the anvil 170. The initiation movement may result in the striker 180 contacting the anvil 170. In addition, this initiation movement may result in the striker 180 moving the anvil 170. For instance, when initiating ahead of a forward drive (e.g. in forward mode) the striker 180 may contact the rear anvil 174. When initiating ahead of a rearward drive (e.g. in reverse mode) the striker 180 may contact the front anvil 172. Whilst this initiation movement may provide a force (e.g. a secondary force) on the anvil system (that is opposite to the primary force), this secondary force is less than the primary force that is imparted when the striker 180 is driven. Accordingly, in forward mode, a secondary force may be imparted rearwards before the striker 180 is driven forwards to provide a primary force forwards. Similarly, in reverse mode, a secondary force may be imparted forwards before the striker 180 is driven rearwards to provide a primary force rearwards. After initiation, the striker 180 is driven to impact the anvil 170 to impart the primary force (e.g. via a tool secured in the attachment coupling 130). In forward mode the striker 180 is driven forwards to impact the front anvil 172 and impart a primary force in the forward direction. In reverse mode the striker 180 is driven rearwards to impact the rear anvil 174 and impart a primary force in the rearward direction. After being driven, the driving mechanism 190 may return the striker to a resting position. If the striker 180 is being driven again (e.g. if the user continues to engage the trigger 140) during forward mode or reverse mode, then the driving mechanism 190 may move the striker 180 back to the initiation position before driving the striker 400 to impact the anvil 170 again. In reciprocating mode, the striker 180 may be moved to the initiation position ahead of the first impact in a similar manner to forward or reverse mode (depending on the direction of the first impact), but after this point the driving process may differ. Instead of using the driving mechanism 190 to move the striker 180 to the initiation position, the striker 180 may instead be driven in the opposite direction to produce an impact with a primary force in the opposite direction. For instance, after a forward impact, the striker 180 may be driven to impact the rear anvil 174 to provide a rearward impact. Similarly, after a rearward impact, the striker 180 may be driven to impact the front anvil 172 to provide a forward impact. In this manner, the anvil system may be reciprocated to provide alternating forward and rearward impact forces. As the range of motion of the striker 180 is greater than the distance between the front anvil 172 and rear anvil 174, the striker 180 may be reciprocated to alternately impact the front anvil 172 and rear anvil 174. This process can continue until the user releases the trigger 140. Reciprocating mode can be useful when performing broaching. In a broaching process, a broaching tool (a broach) is driven into a channel and then is pulled out of the channel. As the tool is pulled out of the channel, debris that has been built up within the channel is pulled out of the channel. This frees up space in the channel for the broach to be further inserted into the channel. By removing debris from the channel, radial forces against the walls of the channel are reduced, thereby reducing the chance of breakage of the material being broached. Broaching may be used to increase the size of a channel or cavity within a bone. For instance, in femoral broaching (e.g. in total hip arthroplasty) a channel is formed in the medullary canal to receiving a femoral stem portion of a hip implant. By reciprocating the broaching tool, debris is cleared from the channel, thereby reducing the risk of radial splitting of the femur during the broaching process. Forward mode can be used to hammer an object. For instance, an implant (e.g. an acetabular cup) may be hammered into a channel or fitting through the use of an adaptor. Reverse mode can be used to pull an object. For instance, a pulling attachment may be connected to, secured to, engaged with, or grip an object, and the reverse mode can be used to pull the object (e.g. pull the object out of another object). For instance, reverse mode can be used to pull (or extract) an implant from a channel or fitting in which the implant is fitted. In addition, reverse mode can be used to help pull a tool or attachment out of an object (e.g. when the tool or attachment becomes lodged or stuck within a cavity). The above description refers to a “resting position” of the anvil 170. It will be appreciated that as the front anvil 172 and the rear anvil 174 are separated from each other, they may have different respective resting positions. The use of the term “resting position” this generally refers to a position particular component (e.g. the anvil 170) when not receiving any external forces. It should be noted that position of the anvil 170 may move depending on external forces being applied to the anvil 170. For instance, if the impactor 100 is being pushed against an object, a rearward force may be applied to the anvil 170. This may move the anvil 170 rearwards within the body 120. Similarly, if the impactor 100 is being pulled away from an object (e.g. through the use of a pulling tool), a forward force may be applied to the anvil 170. This may move the anvil 170 forwards within the body 120. Moving the position of the anvil 170 through the application of external forces (e.g. pushing / pulling the impactor 100) can alter the forces applied by the impactor 100, by adjusting the relative positions of the anvil 170, striker 180 and centring system. The impactor 100 may be powered via a battery (e.g. a removable battery) (not shown). The battery may be aseptic or sterile. The battery may be connected to the base of the impactor 100 (e.g. a bottom of the handle 110) and communication between the battery and controller may be enabled through a hard wire connection. The battery may contain a wireless transmitter / receiver, which can enable the impactor 100 to communicate with external devices. Alternatively, the impactor 100 may comprise a wireless transmitter / receiver. The external device could be a battery charger or a user interface such as a tablet, touchscreen, navigation system, robotic system or smart device. These devices could be used to provide real time information about the impactor 100 and anatomical patient data. For instance, the following data may be output: • Impact energy • Impact force • Impact impulse • Impact frequency • Number of impacts • Attachment or implant displacement (e.g. acetabular cup / broach impaction displacement) • Battery life • Status of the impactor • Bone density / quality In addition to providing information to the user, a user interface could enable the surgeon to adjust impactor parameters such as: • Maximum / minimum energy levels • Frequency • Automatic shut off parameters such as a maximum kinetic energy limit, maximum vibration limit or an anvil minimum displacement limit Figure 3 shows an enlarged view of region A of Figure 2. Figure 4 shows an enlarged view of region B of Figure 2. Sensors are located within the surgical impactor 100 for sensing the motion of various parts of the surgical impactor 100 in use. For instance, one or more first sensors 122 may be positioned within the housing for sensing the displacement (e.g. longitudinal displacement) of the striker 180. In addition or alternatively, one or more second sensors 124 may be positioned within the housing for sensing the displacement (e.g. longitudinal displacement) of the anvil 170. The one or more first sensors 122 and one or more second sensors 124 may be magnetic sensors. For instance, the first and second sensors 122, 124 may be Hall Effect sensors. The one or more first sensors 122 may enable the detection of the displacement of the striker 180 through detecting the magnetic field generated by the magnets 182 contained in the striker 180 (which may be used to drive the striker 180). One or more first sensors 122 may be positioned towards the front of the cavity within the body 120 (towards the front anvil 172) to allow detection of the striker 180 at a forward position and one or more first sensors 122 may be positioned towards the rear of the cavity within the body 120 (towards the rear anvil 174) to enable detection of the striker 180 at a rearward position. The one or more second sensors 124 may enable the detection of the displacement of the anvil 170 based on the magnetic field generated by one or more magnets 178 (referred to herein as “anvil magnets”) connected to the anvil 170. The one or more anvil magnets 178 may be located in one or both of the front anvil 172 and rear anvil 174, and the one or more second sensors 124 may be located at one or both of the front and rear of the cavity. The one or more second sensors 124 may be located further away from the striker 180 (e.g. at a further radial position) than the one or more first sensors 122 to reduce the effect of the striker magnets 182 on the measurements taken by the one or more second sensors 124. In addition, the one or more second sensors 122 may be oriented away from the striker 180 and towards the anvil 170 to reduce the effect of the striker magnets 182 on the measurements taken by the one or more second sensors 124. The one or more first sensors 122 and the one or more second sensors 124 may be positioned outside of (e.g. forward and / or rearward of) the driving mechanism 190 to reduce the effect of any magnetic fields generated by the driving mechanism 190. In addition, one or more vibration sensors (e.g. accelerometers) may be positioned within the surgical impactor 100 to detect the vibration of one or more portions of the surgical impactor 100. For instance, one or more vibration sensors may be connected to the anvil 170 to detect vibration of the anvil 170. In addition, or alternatively, one or more vibration sensors may be connected to the body 120 or handle 110, or any components contained therein (e.g. to detect overall vibration of the surgical impactor 100). Sensor measurements may be sent from the sensors to the processor for analysis. For instance, the one or more first sensors 122 and / or the one or more second sensors 124 may provide magnetic measurements to the processor. The processor may process the magnetic measurements to determine the displacement or location of the striker 180 and / or anvil 170. Similarly, the one or more vibration sensors may send vibration or acceleration measurements to the processor for analysis. The processor may process the sensor measurements and adjust operating parameters and / or the operating mode based on the sensor measurements. Figure 5 shows a plot of velocity over time for the anvil 170 and striker 180 during acceleration and impact. At time a, the striker 180 and anvil 170 are stationary at respective initiating and resting positions. Following time a, the striker 180 is accelerated until it impacts the anvil 170 at time b. At time b the anvil velocity rapidly increases upon impact. Between time b and time c the anvil velocity rapidly decreases due to impact with an external object (e.g. an implant or bone) and / or due to the centring system (e.g. impact with one or more dampers and / or one or more resilient members). In addition, the striker velocity rapidly decreases due to impact with the anvil 170 and, optionally, due to the centring system (either directly, or via the anvil 170). In some instances, a relatively large proportion of the impact force is transferred into the external object (e.g. to move an implant into bone). Conversely, in some other instances, a relatively large proportion of the impact force may be transferred into the centring system (e.g. when the external object does not provide sufficient resistance to prevent the anvil reaching the end of its range of travel). In these other instances, excess energy may cause vibrations that are transferred to the surgeon through the handle 110 as excess HAV. At time c, both the anvil 170 and striker 180 are stationary. Between time c and time d the striker 180 has a negative velocity as it moves back (e.g. rebounds) towards its resting position. This may be caused by the driving mechanism 190 providing a returning force and / or by the centring system providing a returning force (either directly, or via the anvil 170). In addition, the rebound may be caused by rebound forces imparted by the object being impacted. The behaviour of the anvil 170 as it rebounds may vary depending on the type of impact (e.g. the mechanical properties of the object being impacted and / or the attachment, the mode of operation, etc.) As the displacement of the anvil 170 and / or striker 180 may be monitored, the velocity of the anvil 170 and / or striker 180 may be determined. This allows the energy and / or force of the anvil 170 and / or striker 180 to be determined. The kinetic energy E of an object (e.g. the anvil 170 or striker 180) may be calculated as: where m is the mass of the object and v is the velocity of the object. The kinetic energy of an impact can therefore be determined based on the kinetic energy of the striker 180 just before impact (based on the velocity just before impact). The force of the impact is dependent on the kinetic energy at impact. Accordingly, increasing the kinetic energy at impact increases the impact force. When discussing increasing / decreasing impact force, this may refer to the magnitude of the impact force (e.g. irrespective of the direction of impact). Alternatively, the forward and reverse impact forces may be adjusted independently of one another. Given this, it is possible to determine the energy and / or force of an impact based on the speed of the striker 180 at impact. This allows the energy and / or force of an impact to be controlled by controlling the velocity of the striker 180 (e.g. by controlling the driving force applied to accelerate the striker 180). Embodiments described herein are able to monitor the displacement and / or velocity of the anvil 170 and / or striker 180 to determine impact energy and / or impact force. The impact energy and / or impact force can be adjusted to reduce the risk of bone fractures and reduce the risk of user injury. As the impact force is directly dependent on the impact energy, setting a particular impact energy can be considered equivalent to setting a particular impact force (and vice versa). Accordingly, the terms impact force and impact energy may be used interchangeably herein. For instance, according to an embodiment, the impact force may initially be set to be lower for an initial series of impacts, and then may be increased in response to determining that a minimum anvil displacement per impact is reached. This method is particularly suited for forward impacts that are used to broach the cancellous bone or seat an implant within bone. This method allows lower force impacts to be initially performed, when there is a greater chance that the impact trajectory is incorrect (e.g. misaligned), and then increased later when the surgeon has adjusted the impactor to achieve the correct impact trajectory. For instance, during broaching, earlier impacts are more likely to have incorrect broach trajectories, which may lead to localised stresses in the cortical bone (e.g. causing damage to the cortical bone). As the broach advances, the force can be spread over a greater surface area of the bone and therefore the stresses can be reduced. In the case of implant seating, lower forces are desirable until an assessment of bone quality and implant progression has been made. As the tool or implant becomes more firmly embedded, the resistance to each impact will increase, thereby reducing the anvil displacement at each impact. Accordingly, once the anvil displacement is less than a corresponding threshold, it may be determined that the tool or implant is nearly in the desired position. For instance, for a broach, it may be determined that the desired depth has nearly been reached, and for an implant, it may be determined that the implant is nearly fully seated (e.g. to a desired depth). The impact energy may therefore be increased to finally drive in the implant or tool. Once the anvil displacement falls below the corresponding threshold again, it may be determined that the is fully seated to the desired depth or that the broaching has progressed to completion (e.g. to a desired depth, location, direction, and / or orientation). Accordingly, the impacts may be stopped. Figure 6 shows a plot of anvil displacement and impact energy for a series of impacts. The impact energy (and therefore the impact force) is increased over an initial set of impacts (in this case, two impacts) until it reaches a first level. Initially starting with lower force(s) enables the surgeon to find the correct trajectory without administering potentially harmful levels of energy resulting in HAV to the surgeon or risking bone fracture in the patient. The impact force may be set at an initial level (e.g. a minimum level) for the first impact. The impact force may be adjusted based on the anvil displacement to provide an anvil displacement within a predefined range. For instance, if the anvil displacement per impact is below a bottom of the predefined range, the impact force may be increased. If the anvil displacement is above a top of the predefined range, then the impact force may be decreased. If the anvil displacement is within the predefined range, then the impact force may be kept constant. In the present scenario, after this initial set of impacts (i.e. from the second impact onwards) the anvil displacement falls within the predefined range, and so the impact force is kept at the first level and the anvil displacement is monitored. In response to the anvil displacement dropping below a threshold (in this case, at impact 6), the impact energy (and therefore the impact force) is increased to a second level, higher than the first level. This second level may be a maximum impact force (e.g. as set by the user, or as determined based on various parameters, such as bone quality). After the impact force has been increased, the anvil displacement increases due to the increased force. In this case, the anvil displacement increases above the threshold at the seventh impact. Once the anvil displacement falls below the threshold again (in this case, at the eighth impact), the impacts are stopped (i.e. the impactor 100 stops driving the striker 180). Figure 7 shows a method 200 for adjusting impact force based on anvil displacement according to an embodiment. In step S210 the striker 180 is driven to impact at a set impact force. This may include driving the striker 180 to impact the anvil 170 over a series of one or more impacts. The operation of the impactor 100 may be controlled by an operating parameter set defining one or more operating parameters. The operating parameter set may define one or more of: impact force, impact energy, impact frequency, driving force, driving energy, driving current, driving time, driving voltage, operating mode (e.g. forward, reverse, reciprocating, etc.), driving current waveform, driving voltage waveform, etc. Operating parameters may need to be adjusted based on one or more of: the size of bone / joint, bone density, bone quality, procedure type, anatomical variations, implant design, and broach design. The impactor operating parameters may be adjusted by modifying software parameters defining one or more of: forward and / or backward striker speed, power and impaction force, striker force, frequency of operation, and sensitivity of trigger. Accordingly, a first operating parameter set may be applied in step S210, controlling the impactor 100 to drive the striker 180 to provide the set impact force. At least a portion of the first operating parameter set may be defined via user input. In step S220 sensor data is obtained including displacement of the anvil 170 during impact. Optionally, the sensor data may also include vibration data representing vibration of one or more portions of the surgical impactor 100 during impact. The vibration data may be obtained from one or more accelerometers in the surgical impactor 100 recording acceleration and / or rate of change of acceleration. For instance, the sensor data may represent the vibration of the anvil 170, the vibration of the body 120, the vibration of the handle 110, etc. Where multiple impacts are performed in step S210, then sensor data may be obtained for each impact, or may only be obtained for the last impact in the multiple impacts. In step S230 it is determined whether the displacement of the anvil falls outside of a predefined range. This predefined range may be from a lower threshold for displacement to an upper threshold for displacement (the lower threshold being lower than the upper threshold). Where multiple impacts are performed in step S210, then the determination may be based on sensor data for each impact (e.g. the conditions may be applied to each sensor data for each impact, or may be applied to accumulated sensor data, such as an average displacement), or may be based on the last impact in the multiple impacts. If the anvil displacement falls outside of the predefined range, then the method moves on to step S240. If not, then the method loops back to step S210. In step S240 the impact force is adjusted. In response to determining the displacement of the anvil upon impact is less than a lower threshold for anvil displacement, the impact force is increased. In response to determining the displacement of the anvil upon impact is greater than an upper threshold for anvil displacement, the impact force is decreased. The striker 180 may then be driven to impact the anvil 170 according to the adjusted impact force. This may include driving the striker 180 to impact the anvil 170 over a series of one or more impacts. The operating parameter set may be changed to a second operating parameter set to adjust the impact force. When adjusting the impact force, the impact force may be prevented from exceeding a maximum impact force. The maximum impact force may be an initial (first) maximum impact force, set for the current set of one or more impacts. The maximum impact force may be set based on number of factors, either in combination or on their own, including: - Size of anatomy (e.g. bone or joint): Larger joints require larger implants, which in turn require more force / energy. Bone density: Harder, more dense bone will require more force / energy. - Bone quality: Reduced bone quality symptomatic with conditions such as osteoporosis require less force / energy to avoid complications such as bone fracture. - Procedure type: Femoral shaft broaching typically requires less force / energy than acetabular cup seating. - Age of patient: Older patients may have lower bone density / quality, and may therefore require lower impact force / energy. - Anatomical variations: Natural variations in the shape of bones will lead to differences in how implants and tools fit, with some requiring more force / energy than others. - Attachment (e.g. implant / tool) design: Implants are designed with different surface finishes and coatings, and some require more force than others to seat fully. Broaches normally have teeth designed to cut the bone. These teeth have varying degrees of aggressiveness, tooth pitch, size and direction. All of this effects on the amount of force / energy required. As discussed with regard to the method of Figure 8, the maximum impact force may be set lower for an earlier set of impacts and increased for a later set of impacts, for instance, to finally seat an implant. Given the maximum impact force that is set, the adjustment S240 may only be applied if the maximum impact force is not exceeded. For instance, if the adjustment would increase the impact force beyond the current maximum impact force, then the impact force may not be adjusted (e.g. may be maintained at its current level). Following step S240, the method 200 may be repeated at the new (e.g. adjusted) impact force. Accordingly, one or more impacts may be applied at the adjusted impact force, and further adjustments may be made depending on the anvil displacement. Accordingly, the method 200 of Figure 7 may be repeated over a number of iterations, with each iteration adjusting the impact force to attempt to keep anvil displacement within the predefined range. Where multiple iterations are implemented, the predefined range may be kept constant or may be varied. For instance, the lower threshold for anvil displacement may be reduced for one or more later iterations, or may be reduced after each iteration. Once a set number of iterations has been reached, the impacts may be stopped, or the method of Figure 8 may be implemented. Figure 8 shows a method 250 for adjusting maximum impact force based on anvil displacement according to an embodiment. The method of Figure 8 may be implemented instead of the method of Figure 7, after the method of Figure 7 or in parallel with the method of Figure 7. In step S260 the striker 180 is driven to impact at a first impact force. This may include driving the striker 180 to impact the anvil 170 over a series of one or more impacts. This first impact force may be an impact force set by the method of Figure 7 (e.g. an adjusted impact force). The impacts in step S210 may be controlled to be driven at below a first maximum impact force. A first operating parameter set may be applied in step S260, controlling the impactor 100 to drive the striker 180 to provide the first impact force. At least a portion of the first operating parameter set may be defined via user input. In step S270 sensor data is obtained including displacement of the anvil during impact. Where multiple impacts are performed in step S260, then sensor data may be obtained for each impact, or may only be obtained for the last impact in the multiple impacts. In step S280 it is determined whether the displacement of the anvil 170 upon impact is less than a threshold anvil displacement. Where multiple impacts are performed in step S260, then the determination may be based on sensor data for each impact (e.g. the conditions may be applied to each sensor data for each impact, or may be applied to accumulated sensor data, such as an average displacement), or may be based on the last impact in the multiple impacts. If the displacement of the anvil 170 upon impact is less than a threshold anvil displacement, then the method moves on to step S290. If not, then the method loops back to step S260. In step S290 the striker 180 is driven to impact at a second impact force that is greater than the first impact force. This may include driving the striker 180 to impact the anvil 170 over a series of one or more impacts with the second impact force by changing the operating parameter set to a second operating parameter set to increase the impact force. The second impact force may exceed the first maximum impact force. That is, the maximum impact force may be increased to a second maximum impact force that is greater than the first maximum impact force. Following step S290, steps S270 and S280 may be applied for one or more impacts at the second impact force; however, in response to determining that the one or more conditions of step S280 have been met, a different action may be taken. The different action may include increasing the impact force further (e.g. to a third impact force greater than the second impact force), stopping further impacts or reducing the impact force, for instance to the first impact force. Accordingly, the method of Figure 8 may be repeated over a number of iterations, with each iteration increasing the impact force (and potentially increasing the maximum impact force) in response to a positive determination at step S280. Once a set number of iterations has been reached, the impacts may be stopped in response to a positive determination at step S280, or the impact force may be reduced in response to a positive determination at step S280. Where multiple iterations are implemented, the threshold(s) applied in step S270 may be kept constant or may be varied. For instance, the threshold(s) may be reduced each time the impact force is increased. In addition to increasing the impact force, one or more other operating parameters may be changed in step S290. For instance, the impact frequency may be reduced. This can help seat an implant more firmly, and reduce strain on the user. In addition, or alternatively, the operating mode may be changed. For instance, the step S260 the impactor 100 may operate in reciprocal mode (e.g. for use in broaching). In step S290 the operating mode may be changed to a unidirectional mode. For instance, the operating mode may be changed to forward mode so that forward impacts may be used to broach deeper, whilst reducing the risk of damage to the bone due to reverse impacts. Alternatively (or subsequently), the operating mode may be changed to reverse mode to help release the tool from the bone. The method of Figure 7 may be applied before the method of Figure 8. For instance, as shown in Figure 6, an initial set of impacts may be performed with the impact force being dynamically adjusted. In the example of Figure 6, this relates to the ramping up of impact force in impacts 1 and 2. Following impact 2, the method of Figure 8 is applied. In this method, the adjusted impact force from impact 2 is maintained over impacts 3-6. Once the anvil displacement drops below the threshold anvil displacement, the impact force is increased to a higher maximum impact force for two further impacts. Once the anvil displacement drops below the threshold anvil displacement again, the impactor 100 stops impacting. The method of Figure 7 allows impact force to be dynamically adjusted to achieve a desired anvil displacement per impact. The method of Figure 8 allows an initial set of impacts to be performed at a lower impact force to reduce the risk of damage to the object being impacted (e.g. in the case of seating an implant), and then a later set of impacts to be performed at a higher impact force (e.g. to help finally seat the implant). In addition or alternatively to the above, the impactor 100 may monitor vibration levels and take remedial action in response to the vibration level exceeding a maximum vibration threshold. This can help to reduce the risk of injury to the user and damage to the object being impacted (e.g. a bone or implant). Figure 9 shows a method 300 for preventing injury to a patient or surgeon during use of an impactor according to an embodiment. This method may be implemented in parallel to one or both of the methods of Figure 7 and Figure 8. For instance, this method may be implemented for monitoring any impact provided by the impactor 100. In step S310 the striker 180 is driven to impact. This may include driving the striker 180 to impact the anvil 170 over a series of one or more impacts. In step S320 sensor data is obtained representing one or both of displacement of the anvil during impact and vibration of one or more portions of the surgical impactor 100 during impact. The vibration data may be the obtained from one or more accelerometers in the surgical impactor 100. For instance, the vibration data may represent the vibration of the anvil 170, the vibration of the body 120, the vibration of the handle 110, etc. Where multiple impacts are performed in step S310, then sensor data may be obtained for each impact, or may only be obtained for the last impact in the multiple impacts. In step S330 it is determined whether the vibration of the one or more portions of the surgical impactor 100 is greater than a maximum vibration threshold and / or the displacement of the anvil during impact is less than a minimum anvil displacement threshold. Where multiple impacts are performed in step S310, then the determination may be based on sensor data for each impact (e.g. it may be assessed whether the respective thresholds are passed during any of the impacts, or it may be assessed whether the average vibration and / or displacement level is passes the respective threshold), or may be based on the last impact in the multiple impacts. For instance, vibration or displacement may be assessed based on a moving average. If the maximum vibration threshold is exceeded and / or the displacement is less than the minimum anvil displacement threshold, then the method moves on to step S340. If not, then the method loops back to step S310. In step S340 remedial action is taken. A high vibration level can cause injury to the surgeon. Similarly, a low displacement could indicate that excessive energy is being transferred to the patient (e.g. to bone), which could cause damage or injury to the patient (e.g. damage to the bone). Accordingly, one or more of the following actions may be performed: controlling the surgical impactor 100 to stop, or reduce an impact force, of impacts; and issuing an alert. For instance, the remedial action may include stopping the impacts or reducing an impact force. This can help avoid strain on the user due to excessive vibration and / or damage to the patient due to excess impact energy. Similarly an alert may be issued (e.g. to an external device or to a user interface in the surgical impactor 100). For instance, a visual or auditory alert may be issued to alert the user. The user may then, upon noting the alert, control the impactor 100 to stop or reduce the impact force. When stopping an impact force the impactor 100 may stop completely (e.g. stop any form of impact), or may stop impacts in the current mode of operation and change the mode of operation. Changing the mode of operating may inhibit impacts in a particular direction. For instance, if the anvil displacement is less than the minimum anvil displacement threshold when operating in forward mode or reciprocating mode, then the mode may be changed to reverse mode. This is because the attachment may have become stuck within the patient, causing excess energy to be transferred into the patient. In this case, switching the mode of operation to reverse mode (e.g. inhibiting forward impacts) may help to release the attachment. Inhibiting further forward impacts may also avoid causing damage to the bone. In addition or alternatively, a reverse impact force may be increased (e.g. to help dislodge the attachment). When reducing the impact force, the impact force may be reduced in one or both directions depending on the current mode of operation. For instance, when operating in forward mode, the impact force in the forward direction may be reduced. When operating in reverse mode, the impact force in the reverse direction may be reduced. When operating in reciprocating mode, the impact force in one or both directions may be reduced. The force may be reduced in combination with changing the mode of operation. For instance, when operating in forward mode, the impact force in the forward direction may be reduced whilst switching to reciprocating mode. Similarly, when operating in reverse mode, the impact force in the reverse direction may be reduced whilst switching to reciprocating mode. The impact force that is reduced may be one or both of the impact force that the striker 180 is currently being driven to provide (the instantaneous impact force), and the maximum impact force that might set an upper limit above which the impact force may not be increased. For instance, in a combination of the embodiments of Figure 7 and Figure 9, the first impact force may be reduced, and / or the second impact force may be reduced. After step S340, the method of Figure 9 may be repeated (provided that the impactor 100 has not been controlled to completely stop). The method of Figures 7-9 may be implemented in combination. In this scenario, the minimum displacement of the method of Figure 9 may be lower than the lower range of the predefined displacement range of the method of Figure 7. Similarly, the minimum displacement of the method of Figure 9 may be lower than the threshold displacement of the method of Figure 8. That is, the minimum displacement of Figure 9 may be a minimum safe displacement. In addition or alternatively to the above, the impactor 100 may be configured to determine a measure of bone quality based on an amount of displacement during impact. The measure of bone quality may be representative of bone density or bone hardness. Whilst bone quality can be determined from scans of the patient (e.g. bone density can be determined based on x-ray absorption), providing this functionality in the impactor 100 allows a more up to date bone quality measurement to be determined (e.g. at the point of surgery), and can provide a more accurate bone quality measurement. This also avoids the need for conducting a scan of the patient. The measure of bone quality can be used to determine an impact force (e.g. an instantaneous impact force and / or a maximum impact force). For instance, in the embodiments of Figure 7 and 8, the measure of bone quality can be used to define one or more of the set impact force, the first impact force, the second impact force and any maximum impact forces (e.g. the first maximum impact for and / or the second maximum impact force). The measure of bone quality can also be used to determine various thresholds, such as a predefined range (as in the method of Figure 7), a threshold displacement (as in the method of Figure 8), a minimum displacement threshold and / or a maximum vibration threshold (such as those used in the embodiment of Figure 9). Figure 10 shows a surgical impactor 100 including a bone quality tester 132 according to an embodiment. The bone quality tester 132 may be an attachment (e.g. may be removably connected to the surgical impactor 100) or may be integrated within the surgical impactor 100. In the present embodiment, the bone quality tester 132 is an attachment, and therefore can be referred to as a bone quality testing attachment 132. The bone quality tester 132 comprises a tip. In the present embodiment, the tip is sharpened or pointed to form an indent within bone when driven into bone. The tip may be conical. The tip is at a distal end of the bone quality tester 132. The tip may be located at the end of a shaft of the bone quality tester 132. Where the bone quality tester 132 is an attachment, a coupling for coupling to attachment coupling 130 of the surgical impactor 100 may be provided at a proximal end of the bone quality tester 132. In addition, a rest 134 may be provided. The rest 134 may provide one or more points of contact for resting the system against bone to stabilise the system during testing. The rest 134 may be an attachment (e.g. may be removably connected to the surgical impactor 100) or may be integrated within the surgical impactor 100. In the present embodiment, the rest 134 is an attachment. The rest 134 may be connected (either permanently or removably) to the surgical impactor 100 (e.g. to the housing). The rest 134 may form a channel through which the bone quality tester 132 may pass. In the present embodiment, the rest 134 comprises a cylindrical shaft, through which the shaft of the bone quality tester 132 passes. In this embodiment, both the bone quality tester 132 and the rest 134 have circular cross-sections; however, the rest 134 and bone quality tester 132 may have alternative shapes (e.g. alternatively shaped cross-sections). When in a resting position, the tip of the bone quality tester 132 may be aligned with the distal end of the rest 134. When testing bone, the distal end of the rest 134 may be positioned against the bone being tested. When the tip is driven forwards, the tip may protrude out of the rest 134 and indent into the bone. The quality of the bone (e.g. the bone density) may be determined based on the depth of the indent and the force of the impact. For instance, lower quality bone (less dense bone) may be softer, and therefore the indent may be deeper, relative for higher quality bone (more dense bone) for the same force of impact. Given this, the bone quality can be determined by driving the bone quality tester 132 into bone at a known, or predefined, force, and measuring the displacement of the bone quality tester 132. As the bone quality tester 132 is connected to the anvil 170 (either removable connected or permanently connected), the depth of the indent can be determined from the anvil displacement during impact. Bone density can be represented either as a density value (e.g. in g / cm2) or as a T-score. A T-score is a score that represents how close the measured bone density is to the average young adult peak bone density. The lower (e.g. more negative) the T-score, the lower the bone density; whereas the greater the T-score, the higher the bone density. Generally, a T-score of -1.0 or above is considered normal, a score of between -1.0 and -2.5 indicates osteopenia and a score of-2.5 and below indicates osteoporosis. Traditional methods of measuring bone density do so using dual-energy x-ray absorptiometry (DEXA), which measures bone density based on the level of X-ray absorption of the bone. This, however, exposes the patient to high levels of radiation. In addition, whilst it may indicate the bone density at the time of measurement, it does not necessarily indicate the bone density at the point of surgery (which may occur at a different time). In addition, further calculations may be necessary to convert bone density into a measurement of bone strength, bone quality, bone hardness, or the resistance of bone to impacts. By measuring bone quality (e.g. bone density) directly based on the resistance of the bone to impacts by a surgical impactor 100, the bone quality can be assessed directly at the time of surgery. This bone quality measurement can then be used to adjust one or more operating parameters of the surgical impactor 100. For instance, as the bone quality decreases, the bone may become weaker / softer, and therefore less resistant to impacts. Given this, the impact force may be reduced for weaker bone (poorer quality bone) and increased for stronger / harder bone (higher quality bone). In addition, or alternatively, the impact force may be reduced for more brittle bone (lower quality bone). Figure 11 shows a method 400 for determining a measure of bone quality using a surgical impactor 100 according to an embodiment. In step S410, the striker 180 is driven to deliver an impact at a predetermined impact force. This impact is delivered to the bone via the bone quality tester 132 which is attached to the anvil 170. In step S420, sensor data is obtained representing displacement of the anvil 170 during impact. This displacement (e.g. forward displacement) may represent the depth of an indent formed in the bone via the impact. In step S430, the measure of bone quality is determined based on the displacement of the anvil 170 during impact. The measure of bone quality may be the measured displacement itself, or may be a metric derived from the measured displacement. For instance, the measure of bone quality may be a value that is determined through a mapping from anvil displacement. This mapping may be via a parameterized function or may be through a look-up table of predetermined measures of bone quality relative to anvil displacement. The mapping (e.g. function or look-up table) may be determined through calibration by measuring anvil displacement for impacts at the predetermined force for bones with known bone quality (e.g. as determined through DEXA). The measure of bone quality may be a T-score, may be bone density, or may be some other measure of bone quality. The method 400 may be implemented by a computing system. The computing system may comprise a processor configured to control the surgical impactor 100 (e.g. that forms part of the surgical impactor 100). Steps S410 and S420 may be performed by that processor. Step S430 may be performed by the processor within the surgical impactor 100, or may be performed by an external processor. Where step S430 is being performed by an external processor, the anvil displacement may be sent to this external processor by the impactor 100 (e.g. via an output interface, such as a wireless interface), and the external processor may then determine the measure of bone quality based on the anvil displacement. The external processor may communicate the measure of bone quality back to the surgical impactor 100 to allow the surgical impactor 100 to adjust its operating parameter(s). Alternatively or in addition, the external processor may control a display to display the measure of bone quality to the surgeon. Alternatively or in addition, the external processor may calculate adjusted operating parameter(s) and send the adjusted operating parameter(s) to the surgical impactor 100 for use. The external process may determine the adjusted operating parameter(s) based on bone quality. This bone quality may be determined either by the external processor (e.g. based on anvil displacement measurement(s) from the surgical impactor 100) or from an indication of bone quality determined by the surgical impactor 100 and sent to the external processor for analysis. Figure 12 shows a block diagram of a control system 500 for controlling a surgical impactor 100 according to an embodiment. This control system 500 may be integrated within the surgical impactor 100, or may be external to the surgical impactor 100 but communicatively connected to the surgical impactor 100 (e.g. via a wired or wireless connection). The control system 500 includes a bus 510, a processor 520, a memory 530, a persistent storage device 540, an Input / Output (I / O) interface 550. Optionally, the control system 500 may include a network interface (not shown). The bus 510 interconnects the components of the control system 500. The bus 510 may be any circuitry suitable for interconnecting the components of the control system 500. For example, the bus 510 may be an internal bus located on a computer motherboard of the control system 500 or may be a global bus of a system on a chip (SoC). The processor 520 is a processing device configured to perform computer-executable instructions loaded from the memory 530. Prior to and / or during the performance of computer-executable instructions, the processor may load computer-executable instructions over the bus from the memory 530 into one or more caches and / or one or more registers of the processor. The processor 520 may be a central processing unit with a suitable computer architecture, e.g. an x86-64 or ARM architecture. The processor 520 may include or alternatively be specialized hardware adapted for application-specific operations. The memory 530 is configured to store instructions and data for utilization by the processor 520. The memory 530 may be a non-transitory volatile memory device, such as a random access memory (RAM) device. In response to one or more operations by the processor 520, instructions and / or data may be loaded into the memory 530 from the persistent storage device 540 over the bus 510, in preparation for one or more operations by the processor 520 utilising these instructions and / or data. The persistent storage device 540 is a non-transitory non-volatile storage device, such as a flash memory, a solid state disk (SSD), or a hard disk drive (HDD). A non-volatile storage device maintains data stored on the storage device after power has been lost. The persistent storage device 540 may have a significantly greater access latency and lower bandwidth than the memory 530, e.g. it may take significantly longer to read and write data to / from the persistent storage device 540 than to / from the memory 530. However, the persistent storage 540 may have a significantly greater storage capacity than the memory 530. The I / O interface 550 facilitates connections between the control system 500 and other components or devices. The I / O interface 550 may receive signals from a given other component or device (e.g. sensor(s) and / or input device(s)), convert them into a format intelligible by the processor 520 and relay them onto the bus 510 for processing by the processor 520. The I / O interface 550 may also receive signals from the processor 520 and / or data from the memory 530, convert them into a format intelligible by a given external component or device (e.g. a display, audio output (e.g. speaker), light output (e.g. light emitting diode), motor, etc.) and relay them to the given other component or device. The control system 500 may receive sensor data from one or more sensors 560 in the surgical impactor 100. In addition, the control system 500 may receive one or more inputs from one or more input devices 570 of the surgical impactor 100. Based on the sensor data and input(s), the control system 500 is configured to output one or more control signals for controlling the driving mechanism (in this case, a motor 580) of the surgical impactor 100. The inputs from the sensor(s) 560 and / or input device(s) 570 may be received via the I / O interface 550 or may be received directly (e.g. via a direct connection to the processor 520 and / or bus 510). The output to the motor 580 may be sent via the I / O interface 550 or may be sent directly (e.g. via a direct connection from the processor 520 and / or bus 510). A network interface may be provided to facilitate connections between the control system 500 and one or more other computing devices over a network. For example, the network interface may be an Ethernet network interface, a Wi-Fi network interface, or a cellular network interface. As discussed herein, the processor 520 is configured to control the surgical impactor 100 to perform the processes discussed herein. For instance, the processor 520 may be configured to adjust impact force based on one or both of anvil displacement and vibration. In addition, or alternatively, the processor 520 may be configured to adjust one or more operating parameters, stop the impactor, or issue an alert in response to detecting a vibration level that is greater than a maximum vibration threshold. In addition, or alternatively, the processor 520 may be configured to control the surgical impactor 100 to provide one or more impacts having a predetermined impact force, obtain sensor data representing anvil displacement during impact, and determine a measure bone quality based on the anvil displacement. In addition, or alternatively, to the above, the processor 520 may be configured to automatically adjust impact force / energy dependent on how much pre-load the user places on the impactor 100. The pre-load can be determined based on the anvil displacement at rest. When the user pushes the impactor 100 against an object (e.g. bone), the resting position of the anvil 170 (i.e. the position of the anvil 170 when it is not being driven by the driving mechanism 190) will be moved backwards. In this scenario, the impact force may be increased to reflect a desire by the surgeon to more forcefully impact. Depending on the mode, the forward impact force may be increased, or both the forward and backward impact forces may be increased. On the other hand, when the user does not push the impactor 100 against an object, then a lower impact force may be used. In some scenarios, the impactor 100 may be pulled away from an object when an attachment of the impactor is connected to or stuck within the object. In this case, the resting position of the anvil 170 will move forwards. In this scenario, a reverse impact force may be increased. Depending on the scenario, this could help remove the attachment when it is stuck, or help increase the force when the attachment is connected to an implant that is being removed. Whilst particular examples have been provided in the context of hip replacement surgery, embodiments described herein may be utilised in other forms of orthopaedic surgery, such as shoulder replacement, where a glenoid sphere is fitted within a shoulder socket and a humeral stem is fitted within a humeral canal. In addition, whilst various embodiments discuss surgical impactors for use in orthopaedic surgery, the embodiments described herein may be used in other forms of surgery. Given the above, the design and manufacture of implementations of the subject matter and the operations described in this specification can be realized using digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For instance, hardware may include processors, microprocessors, electronic circuitry, electronic components, integrated circuits, etc. Implementations of the subject matter described in this specification can be realized using one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices). Accordingly, embodiments may include transitory or non-transitory computer readable media storing computer-executable code. While certain arrangements have been described, the arrangements have been 5 presented by way of example only, and are not intended to limit the scope of protection. The inventive concepts described herein may be implemented in a variety of other forms. In addition, various omissions, substitutions and changes to the specific implementations described herein may be made without departing from the scope of protection defined in the following claims.

Claims

1. A computer-implemented method for controlling a surgical impactor, the method comprising:controlling the surgical impactor to drive a striker to deliver, via an anvil, one or more impacts at a first impact force;obtaining sensor data representing displacement of the anvil during each of the one or more impacts; andin response to determining the displacement of the anvil upon impact does not meet a displacement condition, adjusting one or more operating parameters of the surgical impactor to adjust the impact force applied by the surgical impactor, wherein the adjusting comprises:in response to determining the displacement of the anvil upon impact is less than a lower threshold for anvil displacement, increasing the impact force; orin response to determining the displacement of the anvil upon impact is greater than an upper threshold for anvil displacement, decreasing the impact force.

2. The method of claim 1 wherein a first maximum impact force is set, and wherein the adjusting does not allow the impact force to be increased beyond the first maximum impact force.

3. The method of claim 2 further comprising:controlling the surgical impactor to drive the striker to deliver, via the anvil, one or more further impacts at the adjusted impact force;obtaining additional sensor data representing displacement of the anvil during each of the one or more further impacts; andin response to determining the displacement of the anvil upon impact during the one or more further impacts is less than a minimum anvil displacement, further adjusting the one or more operating parameters of the surgical impactor to increase the impact force to a second impact force, wherein the second impact force is greater than the first maximum impact force.

4. The method of claim 3 wherein the first impact force and the second impact force are in the same direction.

5. The method of claim 3 or claim 4 wherein the further adjusting comprises reducing an impact frequency.

6. The method of any of claims 3-5 wherein one or more of the first impact force, the second impact force, the first maximum impact force and the second maximum impact force are determined based on a measure of the bone quality of bone being impacted.

7. The method of any of claims 3-6 wherein:prior to the further adjusting, the operating parameter set defines a reciprocating mode to drive the striker to alternately deliver impacts in a first direction and a second direction, wherein the first direction is opposite to the second direction, and wherein the one or more impacts at the first impact force are delivered in the first direction; andafter the further adjusting, the operating parameter set defines a unidirectional mode to provide one or more impacts at the second impact force in the first direction.

8. The method of any of claims 1-6 wherein the operating parameter set defines a unidirectional mode to provide impacts in a first direction.

9. The method of claim 8 further comprising:controlling the surgical impactor to drive the striker to deliver, via the anvil, one or more impacts having a predetermined impact force;obtaining sensor data representing displacement of the anvil during the one or more impacts having the predetermined impact force; anddetermining the measure of the bone quality of the patient based on the displacement of the anvil during the one or more impacts having the predetermined impact force.

10. The method of any preceding claim further comprising:obtaining sensor data representing vibration of one or more portions of the surgical impactor during each of the one or more impacts;in response to determining that the vibration of the one or more portions of the surgical impactor is greater than a maximum vibration threshold, performing one or more of the following actions:controlling the surgical impactor to stop, or reduce an impact force of, one or more future impacts by the surgical impactor; andissuing an alert.

11. A computer-implemented method for controlling a surgical impactor, the method comprising:controlling the surgical impactor to drive a striker to deliver, via an anvil, one or more impacts at a first impact force in a first direction according to a first operating parameter set;obtaining sensor data representing one or both of displacement of the anvil during impact and vibration of one or more portions of the surgical impactor during impact;in response to determining that the vibration of the one or more portions of the surgical impactor is greater than a maximum vibration threshold and / or the displacement of the anvil during impact is less than a minimum anvil displacement threshold, performing one or more of the following actions:controlling the surgical impactor to stop driving the striker in the first direction,controlling the surgical impactor to reduce an impact force of one or more future impacts by the surgical impactor, andissuing an alert.

12. The method of claim 11 wherein controlling the surgical impactor to reduce the impact force of one or more future impacts by the surgical impactor reduces the impact force in the first direction.

13. The method of claim 11 or claim 12 wherein:controlling the surgical impactor to reduce an impact force of one or more future impacts comprises:controlling the surgical impactor to drive the striker according to a second operating parameter set to perform one or both of the following actions:deliver one or more impacts in the first direction at a second impact force that is less than the first impact force; andprovide one or more impacts in a second direction, opposite to the first direction.

14. The method of claim 13 wherein the first operating parameter set defines a first impact frequency and the one or more impacts in the second direction are at a second impact frequency that is less than the first impact frequency.

15. The method of claim 13 or claim 14 wherein the one or more impacts in the second direction are at a third impact force that is greater than the first impact force.

16. The method of claim 13 or claim 14 wherein the one or more impacts comprise a plurality of impacts and the direction of the plurality of impacts alternates between the first direction and a second direction opposite to the first direction, and wherein the method comprises, in response to determining that the vibration of the one or more portions of the surgical impactor is greater than the maximum vibration threshold and / or the displacement of the anvil during impact in the first direction is less than the minimum anvil displacement threshold, controlling the surgical impactor to reduce an impact force of one or more future impacts by the surgical impactor in the first direction or stop future impacts by the surgical impactor in the first direction.

17. The method of any of claims 11-15 wherein the method comprises, in response to determining that the displacement of the anvil during impact is less than the minimum anvil displacement threshold, controlling the surgical impactor to:stop driving the striker in the first direction or reduce an impact force in the first direction; andbegin impacting in a second direction opposite to the first direction or increase an impact force in the second direction.

18. A computer-implemented method for controlling a surgical impactor, the method comprising:controlling the surgical impactor to drive a striker to deliver, via an anvil, one or more impacts having a predetermined impact force;obtaining sensor data representing displacement of the anvil during impact; and determining a measure of bone quality based on the displacement of the anvil during impact.

19. The method of claim 18 further comprising adjusting one or more operating parameters of the surgical impactor that control the driving of the striker based on the determined measure of bone quality.

20. The method of claim 19 wherein the adjusting comprises setting one or more of: an impact force for one or more future impacts, wherein the impact force is lower for lower bone quality and higher for higher bone quality; anda maximum impact force, wherein the maximum impact force sets a force limit for one or more future impacts, and wherein the maximum impact force is lower for lower bone density and higher for higher bone density.

21. The method of any of claims 18-20 wherein the measure of bone quality is determined based on a mapping of bone quality to anvil displacement for the predetermined impact force.

22. The method of any of claims 18-21 wherein the mapping is dependent on one or more patient characteristics.

23. A computer-implemented method for controlling a surgical impactor, the method comprising:determining an amount of force applied to the surgical impactor to push the surgical impactor against an object or pull the surgical impactor away from an object;adjusting a driving force applied by a motor of the surgical impactor to drive a striker to impact an anvil based on the amount of force, wherein a higher driving force is set for a higher amount of force than for a lower amount of force.

24. The method of claim 23, wherein the amount of force is determined based on a position of the anvil within the surgical impactor, wherein the anvil is moved backwards within the surgical impactor in response to the surgical impactor being pushed against the object, and is moved forwards in response to the surgical impactor being pulled away from the object.

25. The method of claim 23 or claim 24 wherein an increased reverse driving force is applied in response to an increased pulling force being applied to the surgical impactorand / or an increased forward driving force is applied in response to an increased pushing force being applied to the surgical impactor.

26. A surgical impactor comprising:a striker;an anvil;a driving mechanism configured to drive the striker to impact the anvil;one or more sensors configured to measure one or both of: displacement of the anvil during impact; and vibration of one or more portions of the surgical impactor during impact;anda processor configured to implement the method of any of preceding claim.

27. The surgical impactor of claim 26 further comprising an attachment coupling connected to the anvil and configured to couple to an attachment for delivering one or more impacts.

28. The surgical impactor of claims 26 or 27 further comprising a bone quality tester for measuring the bone quality, the bone quality tester being connected to the anvil to transfer one or more impacts to impact a bone being tested.

29. The surgical impactor of claim 28 wherein the bone quality tester is removably attached to the anvil.

30. The surgical impactor of claim 28 or claim 29 further comprising a rest extending along at least one side of the bone quality tester and configured to contact the bone being tested at one or more contact points to provide support for the surgical impactor during impact.

31. The surgical impactor of claim 30 wherein the rest is removably attached to the surgical impactor.

32. A processor for controlling a surgical impactor, the processor being configured to implement the method of any of claims 1-25.

33. A computer readable medium comprising computer executable instructions that, when executed by a processor, cause the processor to perform the method of any of claims 1-25.

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