A variable stiffness external fixator for assisting lower limb fracture healing

Abstract

The present invention relates to a variable stiffness external fixator for assisting the healing of lower limb fractures, comprising an internal component arranged outside a bone and fixed to the bone; an external component is arranged outside the internal component; the external component comprises four sub-mechanisms uniformly distributed around the internal component as the center; each sub-mechanism is provided with a motor, a motor seat, a movable part and a connecting part; the motor seat is fixed to the internal component; the motor is used to drive the movable part to rotate on the motor seat; the movable part and the internal component are connected by a flexible translation pair; the connecting part is arranged on one side of the movable part, and the connecting part and the movable part are connected by a flexible rotation pair; the flexible freedom planes of the four sub-mechanisms intersect as a straight line in space, that is, the translation freedom direction of the external fixator. The size and direction of the stiffness can be changed, and the function of adjusting the stiffness can be realized by adjusting the internal component of the external fixator. During the adjustment, the external component remains stationary, which can avoid touching the steel needle and causing needle tract infection.

Description

Technical Field

[0001] The invention belongs to the technical field of rehabilitation robots, and in particular relates to a variable-rigidity external fixator for assisting the healing of lower limb fractures. Background Art

[0002] After a fracture, external objects are needed to reposition and fix the bone, and to take on some of the bone's functions during the recovery period. There are three common fixation methods, including intramedullary fixation, plate fixation, and external fixator fixation.

[0003] Early orthopedic treatment options usually use internal fixation, which can provide solid fixation and allow fracture patients to bear part of the load in the early stages of healing. However, with the in-depth study of the fracture healing process, people have found that appropriate stress stimulation can promote fracture healing, while internal fixation will produce the disadvantage of stress shielding in the later stages of recovery, leading to delayed healing or non-healing of fractures.

[0004] External fixation technology can fix fractures through closed reduction, pin fixation and other effective methods, avoiding surgical tissue incision, effectively protecting the soft tissue around the fracture, and protecting the blood supply to the bones; it has gradually become widely used in the field of orthopedics. In addition, the external fixator installed outside the skin can easily adjust the stiffness, so that it has greater stiffness in the early stage of healing, providing solid fixation for the fracture, and its stiffness can be reduced in the later stage of healing, so that the bones can be properly stressed during rehabilitation exercises, accelerating the recovery process.

[0005] Existing rigidity adjustable external fixators are generally steel plate external fixators, Ilizarov stents, and Taylor space stents.

[0006] Plate external fixation is to insert steel needles into the proximal and distal ends of the fracture (the end close to the heart is called the proximal end, and the other end is the distal end), and connect the steel needles at both ends with the help of a fixator through a connecting rod placed parallel to the bone; during the patient's recovery, the position of the connecting rod is adjusted to change the effective length of the steel needle, thereby changing the stiffness of the entire external fixator. The Ilizarov stent has a single ring or multiple rings distributed in parallel at both ends of the fracture and perpendicular to the bone axis, and is connected to the rings at both ends by a connecting rod parallel to the bone axis; two 90-degree holes are punched at the proximal and distal ends of the patient's fracture, and steel wires are passed through the patient's bones and fixed to the rings at both ends; the stiffness of the entire external fixator is changed by adjusting the preload of the steel wire. The Taylor space stent adjusts stiffness in the same way as the Ilizarov stent, and also changes the stiffness of the entire external fixator by adjusting the preload of the steel wire. Studies have shown that in the process of fracture healing, giving appropriate stress stimulation to the fracture end at different growth periods of the bone can promote the healing process. Appropriate micro-motion of the fracture end can bring about appropriate stress stimulation. Since fracture healing is a bone regeneration process, the mechanical properties of the fracture end will change during the growth process; therefore, in order to achieve the above purpose, the fracture end should be subjected to different micro-motions at different growth stages. The external fixator is "connected in parallel" to the fracture site, which requires the external fixator to have a stiffness adjustment function so that the fracture end can be subjected to different micro-motions at different growth stages; stiffness includes size and direction, and the stiffness size refers to the deformation size of the mechanism under the action of external force; the stiffness direction refers to the direction in which the deformation occurs. The above external fixator can basically adjust the stiffness size, but can only adjust the stiffness size in the direction of the bone axis to produce axial micro-motion of the fracture end. For different growth stages and different fracture types (for example, the fracture section may be a cross section or an inclined section), the axial micro-motion of the fracture end may not necessarily produce appropriate stress stimulation. Therefore, the above external fixator has limitations. In addition, when the above external fixator adjusts the stiffness size, it will directly or indirectly touch the components connected to the bone (steel needles and steel wires), which may cause needle tract infection and complications. Summary of the invention

[0007] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a variable stiffness external fixator for assisting the healing of lower limb fractures, which can change the stiffness size and direction of the external fixator to avoid needle tract infection when adjusting the stiffness direction, and is conducive to assisting the healing of lower limb fractures.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A variable stiffness external fixator for assisting the healing of lower limb fractures, comprising an internal component that is arranged outside a bone and fixedly connected to the bone;

[0010] The outer shell of the inner component is provided with an outer component;

[0011] The external component includes four sub-mechanisms evenly distributed around the internal component;

[0012] Each sub-mechanism is equipped with a motor, a motor seat, movable parts and connecting parts;

[0013] The motor base is fixedly connected to the internal component;

[0014] The motor is fixedly connected to the motor base and is used to drive the movable part to rotate on the motor base;

[0015] The movable part and the internal component are connected through a flexible translation pair;

[0016] The connecting piece is arranged on one side of the movable piece, and the connecting piece and the movable piece are connected via a flexible rotating pair;

[0017] The intersection of the flexible freedom planes of the four sub-mechanisms is a straight line in space, which is the direction of the translational freedom of the external fixator.

[0018] Furthermore, the internal components include a moving ring, a positioning rod and a connecting ring. The two ends of the positioning rod are respectively fixed to the moving ring and the connecting ring. The moving ring is fixed to the bone. The connecting ring and the movable part are connected through a flexible translation pair.

[0019] Furthermore, the flexible translation pair between the movable part and the internal component is a parallel spring mechanism, which includes two parallel springs, one end of which is fixed to a connecting ring, and the other end of which is hinged to the movable part, and the connecting ring is passed through the two parallel springs.

[0020] Furthermore, a parallel spring adjustment plate is provided between the two parallel springs, and the parallel spring adjustment plate, the two parallel springs and the connecting ring are fixedly connected by bolts and nuts.

[0021] Furthermore, a parallel spring adjustment block is clamped between the parallel springs and the parallel spring adjustment plate.

[0022] Furthermore, the parallel springs are fixedly connected with hinged parts, and the hinged parts and the movable parts are hinged to form a rigid rotating pair, and the rigid rotating pair and the rotating axis of the motor coincide with each other.

[0023] Furthermore, the flexible rotation pair between the movable member and the connecting member is a cross spring mechanism, which includes two cross-arranged spring leaves, and two ends of each spring leaf are respectively fixed to the movable member and the connecting member.

[0024] Furthermore, a cross spring leaf adjustment block is clamped between the connecting piece and the spring leaf.

[0025] Furthermore, a rotating member is provided on the motor seat, the motor drives the rotating member to rotate, and the connecting member is fixed to the rotating member.

[0026] Furthermore, a direction marking surface is provided on the rotating member.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. Existing external fixators can often only change the size of stiffness, while the external fixator of the present invention combines the advantages of the flexible kinematic pair and the rigid kinematic pair, realizes the rigid-flexible coupling to complement each other, and can change the size and direction of stiffness. In addition, the functional realization of the present invention is derived from the innovation of configuration, which adopts the method of changing the posture of the sub-mechanism and changing the constraint of the overall mechanism to realize the change of the direction of the degree of freedom.

[0029] 2. When adjusting the rigidity of the traditional external fixator, it is easy to touch the steel needle and cause needle tract infection. However, the present invention, through the reasonable layout of the mechanism, can achieve the function of adjusting the rigidity by simply adjusting the internal components of the external fixator. During adjustment, the external components remain stationary, which can avoid touching the steel needle and causing needle tract infection. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the three-dimensional structure of this embodiment (the dotted box represents a quarter of the mechanism).

[0031] Figure 2 It is a three-dimensional structural schematic diagram of the internal mechanism of this embodiment.

[0032] Figure 3 A schematic diagram of the three-dimensional structure of a quarter mechanism of this embodiment.

[0033] Figure 4 A schematic plan view of one degree of freedom of a quarter mechanism of this embodiment.

[0034] Figure 5 Schematic diagram of the direction of translational freedom of the external fixator of this embodiment.

[0035] Figure 6 A schematic plan view of one degree of freedom of a quarter mechanism behind the driving motor of this embodiment.

[0036] Figure 7 Schematic diagram of the direction of translational freedom of the external fixator after the motor is driven in this embodiment.

[0037] In the figure:

[0038] 1-quarter mechanism, 2-proximal bone, 3-moving ring, 4-top ring, 5-connecting ring, 6-base, 7-distal bone, 8-bone callus, 9-steel needle, 10-steel needle seat, 11-positioning rod, 12-motor, 13-motor seat, 14-one-eighth mechanism, 15-flexible rotation pair, 16-rigid rotation pair, 17-parallel spring adjustment plate, 18-mounting hole, 19-parallel spring mechanism, 20-cross spring mechanism, 21-one degree of freedom plane, 22-flexible translation pair moving direction line, 23-parallel spring adjustment block, 24-parallel spring, 25-movable part, 26-hinge, 27-spring leaf, 28-cross spring adjustment block, 29-rotating part, 30-connecting part, 31-towards the marking surface, 32-direction of the translational freedom of the external fixator. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with examples and drawings, but the embodiments of the present invention are not limited thereto.

[0040] like Figure 1 , 2 As shown, the variable stiffness external fixator for assisting the healing of lower limb fractures is a translation mechanism with a single degree of freedom, including an internal mechanism and an external mechanism.

[0041] The internal mechanism is sleeved outside the bone, and includes a moving ring 3, a positioning rod 11 and a connecting ring 5 arranged from top to bottom. The two ends of the positioning rod 11 are respectively fixed to the moving ring 3 and the connecting ring 5, and are preferably integrally formed.

[0042] The external mechanism includes four identical sub-mechanisms (hereinafter referred to as quarter mechanisms 1), which are evenly distributed outside the internal mechanism in a cross shape. Each quarter mechanism 1 is provided with a top ring 4, a motor seat 13 and a base 6. The upper and lower ends of the motor seat 13 are respectively fixed to the top ring 4 and the base 6. The top ring 4 is sleeved outside the moving ring 3.

[0043] The four quarter mechanisms 1 are arranged symmetrically and vertically mounted on the base 6. The top ring 4 is horizontally mounted on the top of the four quarter mechanisms 1. The moving ring 3 and the connecting ring 5 are both kept horizontally connected by bolts. The connecting ring 5 is connected by bolts as shown in the figure. Figure 3 The mounting holes 18 shown are respectively fixed to the four quarter mechanisms 1 .

[0044] The fractured bone is divided into two sections with the fracture site as the boundary, including the proximal bone 2 and the distal bone 7. The steel needles 9 are respectively driven into the proximal bone 2 and the distal bone 7 at the fracture site. The steel needles 9 on the proximal bone 2 are fixed to the moving ring 3 through the steel needle holder 10, and the steel needles 9 on the distal bone 7 are fixed to the base 6 through the steel needle holder 10, so that the entire external fixator is "connected in parallel" with the bone and can play a role in bearing the load.

[0045] like Figure 3As shown, each quarter mechanism 1 is provided with two identical eighth mechanisms 14 at intervals.

[0046] The one-eighth mechanism 14 is provided with a parallel leaf spring mechanism 19 and a cross leaf spring mechanism 20 .

[0047] like Figure 4 As shown, the parallel spring mechanism 19 includes a parallel spring adjustment block 23, a parallel spring 24 and a hinge 26. The parallel spring adjustment block 23 is clamped between the parallel spring 24 and the parallel spring adjustment plate 17, and one end thereof is threaded, and its position between the parallel spring 24 and the parallel spring adjustment plate 17 can be locked by means of a bolt. Figure 3 The mounting hole 18 shown penetrates the parallel spring adjustment plate 17 and the two parallel springs 24, and the parallel spring adjustment plate 17, the parallel springs 24 and the connecting ring 5 are fixed together by bolts and nuts. The other end of the parallel spring 24 is fixed to the hinge 26. The cylindrical part of the movable part 25 in the cross spring mechanism 20 is connected to the hinge 26 through a bearing to form a rigid rotating pair 16; the rotating part 29 is arranged horizontally with the motor seat 13, and the rotating part 29 is fixedly connected to the shaft of the motor 12.

[0048] The cross spring mechanism 20 includes a rotating member 29, a connecting member 30, a spring leaf 27, a movable member 25 and a cross spring adjustment block 28. The two spring leaves 27 are cross-fixed between the movable member 25 and the connecting member 30, and a gap is left between the two spring leaves 27. The cross spring adjustment block 28 is stuck between the connecting member 30 and the spring leaf 27, and one end of the cross spring adjustment block 28 can be locked in position between the connecting member 30 and the spring leaf 27 by means of a bolt. The connecting member 30 and the rotating member 29 are fixed together. Since the spring leaf 27 is fixed on two rigid components, when subjected to external force, it is mainly the spring leaf 27 that is deformed, and the two cross-arranged spring leaves 27 can be approximately regarded as a flexible rotating pair 15 rotating around its cross axis, as shown in FIG. Figure 3 As shown, the cross leaf spring mechanism 20 can be regarded as a flexible rotation pair 15 between the movable member 25 and the connecting member 30. Similarly, the parallel leaf spring mechanism 19 can be approximately regarded as a flexible translation pair moving along the plane normal of the two parallel leaf springs 24. Therefore, the parallel leaf spring mechanism 19 can be approximately regarded as a flexible translation pair between the hinge 26 and the connecting ring 5.

[0049] Furthermore, since the cross leaf spring mechanism 20 and the parallel leaf spring mechanism 19 can be approximately regarded as flexible kinematic pairs, under the rotation angle of the given motor 12, the quarter mechanism 1 has a flexible translation pair, two flexible rotation pairs 15 and two rigid rotation pairs 16. According to the relationship between motion and constraint, the quarter mechanism 1 has two translational degrees of freedom, forming a degree of freedom plane 21, which contains the flexible translational pair moving direction line 22 and is parallel to the plane of the rotation member 29 facing the marking surface 31. According to the characteristics of the parallel connection of the mechanism, the degree of freedom of the external fixator of this embodiment will be the intersection of the degree of freedom planes of all the quarter mechanisms 1. Under the premise of satisfying the above-mentioned geometric constraints, the flexible degree of freedom planes of the four quarter mechanisms 1 intersect as a straight line in space, which is the translational degree of freedom direction 32 of the external fixator.

[0050] Furthermore, since the translational freedom direction 32 of the external fixator is the intersection of the freedom planes of each quarter mechanism 1, the freedom of the external fixator can be controlled by controlling the freedom planes of each quarter mechanism 1. Since the axis of the rigid revolving pair 16 coincides with the rotation axis of the motor 12, Figure 5 As shown, the cross leaf spring mechanism 20 can be driven to rotate by driving the motor 12, while the position of the parallel leaf spring mechanism 19 does not change, but the orientation mark surface 31 on the rotating member 29 changes, so that the freedom plane of the quarter mechanism 1 changes. By driving the motors 12 on the other quarter mechanisms 1 and changing their freedom planes, the freedom of the entire external fixator can be controlled over a wide range.

[0051] Furthermore, changing the degree of freedom of the external fixator means changing the direction in which it deforms, that is, changing the direction of its stiffness. In addition, the rotation of the drive motor 12 only changes the angle of the cross-leaf spring mechanism 20, and does not change the position and posture of the parallel-leaf spring mechanism 19. Therefore, during the process of the drive motor 12 changing the stiffness direction of the external fixator, the parallel-leaf spring mechanism 19 is stationary. Therefore, it does not affect the internal mechanism and touch the steel needle 9, thus avoiding the needle track loosening and causing infection.

[0052] Furthermore, the positions of the parallel spring adjustment block 23 and the cross spring adjustment block 28 can be adjusted to change the effective length of the corresponding springs, thereby changing the deformation of the external fixator, that is, changing the stiffness. Adjusting the positions of the parallel spring adjustment block 23 and the cross spring adjustment block 28 will not affect the internal mechanism and touch the steel needle 9, thereby avoiding infection caused by loose needle tract.

[0053] Furthermore, the external fixator of this embodiment realizes the function of changing the size and direction of stiffness by adjusting the internal components of the mechanism. When the patient is doing rehabilitation exercises (standing or walking slowly), it is equivalent to applying an axial force to the proximal bone 2 and the distal bone 7 respectively; under the action of the axial force, the connecting ring 5 is constrained by each quarter mechanism 1, which will produce micro-motion along the translational freedom direction 32 of the external fixator, driving the internal mechanism to move; and then causing the proximal bone 2 to micro-move. Appropriate micro-motion will bring about appropriate stress stimulation. According to the theory that stress stimulation promotes the proliferation and differentiation of bone tissue, it can promote the transformation of the callus 8 grown at the fracture site into mature bone as soon as possible.

[0054] The size and direction of the micro-motion are determined by the size and direction of the stiffness of the external fixator. By adjusting the stiffness of the external fixator, the patient is subjected to appropriate micro-motion at different stages of bone growth, that is, appropriate stress stimulation; according to the theory in orthopedics that stress stimulation promotes bone tissue proliferation and differentiation, stress stimulation can promote fracture healing. Therefore, the external fixator of this embodiment can achieve the purpose of assisting the healing of lower limb fractures.

[0055] The steps for achieving variable stiffness of the external fixator of this embodiment are as follows:

[0056] Obtain appropriate micro-motion, and based on the micro-motion, obtain the required stiffness direction and magnitude;

[0057] Solve the degree of freedom plane of each quarter mechanism 1 and the position of each reed adjustment block;

[0058] According to the direction of each quarter mechanism 1 degree of freedom plane, the corresponding direction toward the marking surface 31 is calculated;

[0059] The motor 12 is controlled to rotate so that the cross spring mechanism 20 reaches a position facing the target marking surface 31;

[0060] Move the reed adjustment block to the target position.

[0061] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A variable stiffness external fixator for assisting the healing of lower limb fractures, characterized in that: It includes an internal component that is disposed around the outside of the bone and is fixedly connected to the bone; The outer shell of the inner component is provided with an outer component; The external component includes four sub-mechanisms evenly distributed around the internal component; Each sub-mechanism is equipped with a motor, a motor seat, movable parts and connecting parts; The motor base is fixedly connected to the internal component; The motor is fixedly connected to the motor base and is used to drive the movable part to rotate on the motor base; The movable part and the internal component are connected through a flexible translation pair; The connecting piece is arranged on one side of the movable piece, and the connecting piece and the movable piece are connected via a flexible rotating pair; The intersection of the flexible freedom planes of the four sub-mechanisms is a straight line in space, which is the direction of the translational freedom of the external fixator; The internal components include a moving ring, a positioning rod and a connecting ring, the two ends of the positioning rod are respectively fixed to the moving ring and the connecting ring, the moving ring is fixed to the bone, and the connecting ring is connected to the movable part through a flexible translation pair; The flexible translation pair between the movable part and the internal component is a parallel spring mechanism, which includes two parallel springs, one end of which is fixed to a connecting ring, and the other end of which is hinged to the movable part, and the connecting ring is arranged between the two parallel springs; A parallel spring adjustment plate is provided between the two parallel springs, and the parallel spring adjustment plate, the two parallel springs and the connecting ring are fixedly connected by bolts and nuts; A parallel spring adjustment block is clamped between the parallel spring and the parallel spring adjustment plate; The parallel springs are fixedly connected with a hinged part, the hinged part and the movable part are hinged to form a rigid rotating pair, and the rigid rotating pair and the rotating axis of the motor coincide with each other; The flexible rotating pair between the movable member and the connecting member is a cross spring mechanism, which includes two cross-arranged spring leaves, and the two ends of each spring leaf are respectively fixed to the movable member and the connecting member; A cross spring leaf adjusting block is clamped between the connecting piece and the spring leaf.

2. A variable stiffness external fixator for assisting lower limb fracture healing according to claim 1, characterized in that: A rotating part is arranged on the motor seat, the motor drives the rotating part to rotate, and the connecting part is fixedly arranged on the rotating part.

3. A variable stiffness external fixator for assisting lower limb fracture healing according to claim 1, characterized in that: The rotating part is provided with a direction marking surface.

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