Bone fixation assembly for endoprosthetic reconstruction

Abstract

A bone attachment assembly is provided for securing an orthopaedic implant to a resected bone portion. The assembly comprises a compress spindle having an interface surface configured to engage the resected end of a bone portion, an anchor plug configured for securement within an intramedullary canal of the bone portion, and a traction member extending between the compress spindle and the anchor plug. The traction member is configured to apply compressive force along a longitudinal axis between the compress spindle and the anchor plug, and is further configured to bend to permit relative movement between the compress spindle and the anchor plug in a direction transverse to the longitudinal axis. This configuration allows the assembly to accommodate non-coaxial alignment between the spindle and the anchor plug while maintaining axial compression.

Description

Bone Fixation Assembly for Endoprosthetic ReconstructionField of the Invention

[0001] The present invention relates to orthopaedic fixation systems, and more particularly to a bone attachment assembly for securing an implant to a resected end of a long bone. The assembly is intended for use in complex orthopaedic reconstructions, such as those following oncological resection, trauma, or revision of failed implants. The invention is particularly applicable to fixation within the intramedullary canal of long bones including the femur, humerus, tibia, ulna, and radius, and is directed to addressing mechanical and biological limitations associated with conventional stem-based fixation methods.Background of the Invention

[0002] Compressive osseointegration devices are designed to provide stable fixation within the intramedullary canal of long bones, including the femur, tibia, humerus, ulna, and radius. These devices are particularly suited to complex reconstruction procedures following extensive bone resection due to oncologic pathology or the failure of previous orthopaedic implants. In such contexts, maintaining reliable mechanical fixation while encouraging biological integration is essential for long-term clinical success.

[0003] Historically, intramedullary fixation has been achieved using stem-based implants, which are inserted into the canal and rely on press-fit or cemented engagement with the endosteal surface. While widely adopted, such stems can lead to complications including aseptic loosening and stress shielding. These issues arise from the tendency of rigid stems to divert physiological load away from the surrounding bone, thereby reducing mechanical stimulation and leading to bone resorption over time.

[0004] In contrast, compressive osseointegration systems aim to preserve or restore the natural load transmission pathway by applying an axial compressive force across the bone-implant interface. This is achieved by drawing an anchor plug and a compress spindle into opposing contact with the bone, thereby preloading theinterface under controlled tension. The compressive force promotes osseointegration by stimulating bone growth at the implant interface, and can also assist in maintaining mechanical stability in the absence of extensive stem anchorage.

[0005] Certain transdermal prosthesis systems, such as those described in US 2014 / 0214177 A1 (BIOMET MFG CORP) 31 July 2014 "Transdermal Intraosseous Device" and US 2014 / 0228973 A1 (BIOMET MFG CORP) 14 August 2014 "Transdermal Prosthesis", disclose examples of bone-anchored prosthetic systems that involve interface components positioned at the resected bone surface and anchoring structures within the medullary canal. These disclosures illustrate some of the foundational concepts in endoprosthetic fixation, including various anchoring and interface strategies.

[0006] However, traditional stem-based implants of the type exemplified in these references may be prone to instability and long-term failure due to aseptic loosening, stress shielding, and insufficient bone integration issues.

[0007] It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country.Summary of the Disclosure

[0008] A bone attachment assembly is provided, comprising a compress spindle having an interface surface configured to engage a resected end of a bone portion, an anchor plug configured for securement within an intramedullary canal of the bone portion, and a traction member extending between the compress spindle and the anchor plug. The traction member is configured to apply compressive force along a longitudinal axis defined between the compress spindle and the anchor plug, drawing the spindle into compressive engagement with the resected bone surface.

[0009] The traction member is further configured to bend to permit relative movement between the compress spindle and the anchor plug in a direction transverse to the longitudinal axis. This bending capability enables the assembly to tolerate misalignment between the anchor plug and the spindle, such as may occur duringimplantation or due to anatomical variation, without transmitting excessive shear or torsional stress to the bone interface.

[0010] The ability of the traction member to accommodate transverse movement while maintaining axial compression may reduce the incidence of micromotion at the boneimplant interface. This contributes to improved mechanical stability during the early post-operative period and supports bone ingrowth by maintaining continuous compressive contact at the interface surface.

[0011] The design of the assembly facilitates a load-sharing construct in which physiological forces are transferred through the bone rather than through a rigid stem. This may assist in mitigating stress shielding and preserving bone stock adjacent the resection site.

[0012] The transverse compliance of the traction member may further mitigate off- axis loading conditions that can arise from imperfect alignment between the spindle and the anchor plug. By absorbing or deflecting bending moments that would otherwise be transmitted through a rigid traction member, the system may reduce the risk of fatigue failure at the junction between components and maintain compressive preload over time.

[0013] The bone attachment assembly thereby provides a construct capable of maintaining axial compression across the bone interface while tolerating transverse movement or misalignment, enhancing mechanical compatibility with the native anatomy and reducing the risk of implant failure due to alignment-related stresses.

[0014] In some embodiments, the interface surface of the compress spindle may define one or more anti-rotation features configured to inhibit rotational displacement of the bone portion relative to the spindle. These features may assist in maintaining mechanical stability at the bone-implant interface under torsional loads.

[0015] The anti-rotation features may include a plurality of chocks projecting from the interface surface. These chocks can engage irregularities in the resected bone surface to resist rotational movement during functional loading.

[0016] In alternative embodiments, the anti-rotation features comprise a plurality of longitudinal spikes extending from the interface surface along the longitudinal axis.These spikes may penetrate the trabecular bone structure to achieve rotational restraint.

[0017] The longitudinal spikes may be embedded in a compressible polymeric medium provided on the interface surface. Upon assembly and axial compression, the medium may deform to expose the tips of the spikes, facilitating improved interdigitation with cancellous bone while accommodating minor surface irregularities. Alternatively, the longitudinal spikes may protrude directly from the interface surface without an intervening polymeric medium, providing immediate mechanical engagement upon contact with the resected bone.

[0018] In some forms, the anti-rotation features may be configured to engage cancellous bone specifically, reducing or eliminating relative rotation between the compress spindle and the bone portion under applied torsional loads.

[0019] Preferably, the traction member comprises a flexible cable. The flexibility of the cable permits the traction member to accommodate angular deviations between the anchor plug and the compress spindle while preserving axial tension.

[0020] In certain embodiments, the anchor plug defines a cable connector interfacing a distal end of the cable. The cable connector may be crimped, clamped, or otherwise fixed to the cable to establish a secure mechanical connection.

[0021] Additionally or alternatively, the traction member may comprise a traction bar interfacing with a proximal end of the cable via a corresponding cable connector. This bar may facilitate axial adjustment and force transmission within the spindle assembly.

[0022] The compress spindle may define a channel slidably engaging the cable connector of the traction bar in the axial direction. This configuration may allow controlled tensioning of the traction member during implantation.

[0023] The cable may comprise braided wire to provide high tensile strength and resistance to kinking or torsional failure during cyclic loading.

[0024] In other embodiments, the cable comprises nitinol, a shape memory alloy known for superelasticity. Nitinol cables may enhance fatigue resistance and preserve mechanical function following repeated deformation.

[0025] The compress spindle may further define an elongate centering post extending in the axial direction from the interface surface. The centering post may assist in resisting bending loads and guide alignment during implantation.

[0026] The centering post may have a uniform longitudinal profile to provide consistent intramedullary engagement. This profile may be selected to match the geometry of the medullary canal for enhanced stability.

[0027] The uniform profile of the centering post may be conical, allowing progressive engagement and self-centring during insertion. In alternative forms, the uniform profile may be cylindrical, which may facilitate rotational stability and simplify manufacturing.

[0028] The centering post may comprise a smooth surface to facilitate insertion into the canal and reduce friction during implantation. The smooth surface of the centering post may be polished, further reducing insertion resistance and minimising disruption to the endosteal surface of the canal.

[0029] In some embodiments, the centering post slidably contains a cable connector of the traction member, allowing the connector to be housed entirely within the post and aligned coaxially with the longitudinal axis.

[0030] In other configurations, a cable connector of the traction member may extend beyond the centering post. This arrangement may be used where a shorter centering post is preferred due to anatomical constraints.

[0031] Other aspects of the invention are also disclosed.Brief Description of the Drawings

[0032] Notwithstanding any other forms which may fall within the scope of the present invention, preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[0033] Figure 1 shows a perspective view of a bone attachment assembly in accordance with a first embodiment, showing the overall structure including the compress spindle, anchor plug, and traction member.

[0034] Figure 2 shows a cross-sectional view of the bone attachment assembly, illustrating the internal configuration and interaction between the compress spindle, anchor plug, and traction member.

[0035] Figure 3 shows a perspective view of a second embodiment of the assembly with a shorter centering post, showing how the cable connector could extend beyond the centering post.

[0036] Figure 4 shows a cross-sectional view of the second embodiment, highlighting the cable connector’s position relative to the centering post.

[0037] Figure 5 shows a perspective view of a bone attachment assembly in accordance with a third embodiment, showing the overall structure including the compress spindle, anchor plug, and traction member.Description of Embodiments

[0038] Figures 1 and 2 show perspective and cross-sectional views of a bone attachment assembly 100 for endoprosthetic reconstruction in accordance with a first embodiment. Figures 3 and 4 illustrate respective views of a second embodiment, and Figure 5 shows a perspective view of a third embodiment of the assembly 100.

[0039] The assembly 100 comprises a proximal compress spindle 101 defining an axially oriented interface surface 105 configured for engaging a resected end of a bone portion in use. The interface surface 105 may be concave to promote central seating of the bone portion relative to the spindle 101 , thereby facilitating uniform load distribution and stable contact.

[0040] The interface surface 105 may further define anti-rotation features. In the embodiment shown in Figure 1 , these features comprise chocks 1 14; in alternative embodiments, such as those shown in Figure 5, the features comprise a series of longitudinal spikes 1 18 protruding along the longitudinal axis. These spikes 1 18 serve to reduce or eliminate rotational displacement of the bone portion relative to the spindle 101 . In certain embodiments, the spikes 1 1 8 may stand alone on the interface surface 105; in others, they may be embedded in a compressible polymeric medium 1 19 that exposes the spike tips upon compression, enhancing engagement with the cancellous bone surface while accommodating irregularities in the resected surface.

[0041] The assembly 100 further comprises a distal anchor plug 102 configured for securement within the intramedullary canal of the bone portion. The anchor plug 102 may include a series of apertures 1 15 for receiving transverse cortical screws or pins, thereby anchoring the plug 102 rigidly to the surrounding cortical bone.

[0042] The assembly 100 further comprises a traction member 103 extending between the compress spindle 101 and the anchor plug 102. The traction member 103 is configured to apply a compressive force along a longitudinal axis defined between the compress spindle 101 and the anchor plug 102. In use, the traction member 103, anchored distally by the anchor plug 102, acts in the axial direction to pull the interface surface 105 of the compress spindle 101 into compressive contact with the resected end of the bone portion, thereby promoting osseointegration through controlled axial loading.

[0043] The compress spindle 101 may define a Morse taper profile 120 to provide a secure and repeatable mechanical interface with a complementary female taper adapter (not shown), enabling modular attachment of joint components or extension constructs.

[0044] The traction member 103 is further configured to permit deflection or transverse compliance to accommodate relative displacement between the compress spindle 101 and the anchor plug 102 in a direction transverse to the longitudinal axis. This compliance may be achieved through one or more structural features of the traction member 103, such as material flexibility, articulation, segmentation, or mechanical play, and is not limited to components that bend by elastic deformation. This design feature enables the assembly 100 to tolerate minor misalignment between the compress spindle 101 and the anchor plug 102 during implantation or as a result of anatomical variation, without introducing off-axis torsional loads that could compromise the fixation interface. The ability of the traction member 103 to permit non-axial adjustment improves construct stability by reducing stress concentrations at the interface surface 105 of the compress spindle 101 , facilitating uniform load transfer, and reducing the risk of failure associated with micromotion or localised bone resorption.

[0045] In the preferred embodiment shown, the traction member 103 comprises a flexible cable 104. The use of a cable provides high tensile strength with inherent bending flexibility, allowing the traction member 103 to conform to non-linear alignment between the anchor plug 102 and the spindle 101 while maintaining axial preload. The cable construction also introduces damping characteristics that may reduce peak stress transmission during physiological loading.

[0046] The anchor plug 102 may define a cable connector 106A interfacing with a distal end of the cable 104. The cable connector 106A may be tubular and envelop the distal end of the cable 104. The distal cable end may be secured within the connector 106A using various techniques, including crimping, clamping, soldering, or mechanical compression fittings.

[0047] The traction member 103 may also comprise a proximal traction bar 107 that is slidably received within the compress spindle 101. The traction bar 107 may define a distal cable connector 106B similar to that of the anchor plug 102, enabling integration with the proximal end of the cable 104. The compress spindle 101 may define an internal channel 1 16 for axially slidable engagement with the cable connector 106B, allowing controlled axial displacement and facilitating tensioning during assembly.

[0048] In the preferred embodiment, the cable 104 comprises braided wire, offering a balance of tensile strength and torsional flexibility. In alternative embodiments, the cable 104 comprises nitinol, a nickel-titanium alloy exhibiting shape memory and superelasticity. These properties allow the cable to recover its original form after deformation and endure repeated flexural strain without permanent deformation, enhancing fatigue resistance and longevity under physiological loading conditions.

[0049] A proximal end of the traction bar 107 may include threading 108 for engagement with a nut 109, which may be tightened against a compressive resistance element 1 10. The resistance element 1 10 may include a stack of conical spring washers arranged to provide a controlled compressive preload. The nut 109 may define an annular flange 1 1 1 , which is retained by an internal rim 1 12 of the compress spindle 101 to prevent disengagement under tension.

[0050] The compress spindle 101 may further define an elongate centering post 1 17 projecting axially from the interface surface 105. The centering post 1 17 is configured to enter the intramedullary canal of the bone portion and resist bending moments applied between the compress spindle 101 and the bone. Preferably, the centering post 1 17 has a polished surface to facilitate insertion and compliant engagement. It may have a uniform longitudinal profile, which may be slightly tapered (i.e., conical) or cylindrical, to provide consistent intramedullary contact and resist eccentric loads.

[0051] In the embodiment shown in Figures 1 and 2, the centering post 1 17 is elongate, for example 5 cm or longer, and configured to contain the cable connector 106B entirely within its intramedullary length. In contrast, the embodiment shown in Figures 3 and 4 features a shorter centering post 1 17, for example less than 2 cm in length, such that the cable connector 106B extends beyond the centering post 1 17 and into the medullary canal. This configuration may be preferred in anatomical regions with shorter available canal length or to accommodate angled implantation paths.

[0052] An exemplary surgical method of installing the bone attachment assembly 100 begins with the resection of the target bone portion, such as a femur, tibia, humerus, or other long bone, to remove diseased or damaged tissue. The resection plane may be prepared using standard orthopaedic saw guides to create a transverse or oblique cut suitable for interfacing with the compress spindle 101 .

[0053] Following resection, the intramedullary canal of the bone is prepared to receive the anchor plug 102. Canal preparation may involve reaming or broaching to an appropriate diameter to accommodate the outer profile of the anchor plug 102, ensuring cortical engagement for fixation. The prepared canal may then be assessed for alignment with the intended spindle trajectory, although perfect coaxial alignment is not required due to the compliant nature of the traction member 103.

[0054] The anchor plug 102 is inserted into the prepared intramedullary canal. Transverse cortical screws or pins may be inserted through the apertures 1 15 in the anchor plug 102 to achieve secure fixation to the cortical walls of the bone. These fasteners provide rotational and axial stability of the anchor plug 102 during and afterassembly of the implant. The optional centering post 1 17 of the compress spindle 101 may be inserted into the intramedullary canal to resist bending forces and assist with mechanical alignment.

[0055] The threading 108 of the traction bar 107 may be engaged with the nut 109, which is rotated to apply compressive preload between the compress spindle 101 and the anchor plug 102. The preload may be regulated by the stack of conical spring washers comprising the compressive resistance element 1 10, which allows gradual and controlled force application. This preload draws the spindle 101 against the resected end of the bone, placing the interface surface 105 in firm contact with the bone portion.

[0056] Where present, anti-rotation features such as chocks 1 14 or spikes 1 18 assist in preventing rotational slippage between the bone and the spindle 101 both during implantation and following surgery. The optional compressible polymeric medium 1 19 may conform to the cancellous bone surface during compression, exposing the embedded spike tips and enhancing interface grip, particularly in irregular or osteoporotic bone.

[0057] The configuration of the traction member 103 allows for bending compliance during implantation and post-operative loading. If the intramedullary canal is not precisely coaxial with the resected surface, the flexible cable 104 accommodates the angular offset without transmitting excessive shear forces to the bone-implant interface. This tolerance to non-coaxiality reduces the need for precise intraoperative alignment and enables implantation in complex anatomical geometries.

[0058] By maintaining axial compression while allowing for bending displacement and resisting torsional movement through anti-rotation features, the assembly 100 supports stable initial fixation and promotes bone integration through physiological load sharing. The system may reduce micromotion at the bone-spindle interface, mitigating risks associated with aseptic loosening or stress shielding. The design also accommodates anatomical variation and may simplify surgical workflow by reducing alignment constraints typically required in rigid intramedullary fixation systems.

[0059] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that specific details are not required in order to practise the invention. Thus, the foregoing descriptions of specific embodiments of the invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed as obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.

Claims

Claims1 . A bone attachment assembly comprising: a compress spindle having an interface surface configured to engage a resected end of a bone portion; an anchor plug configured for securement in an intramedullary canal of the bone portion; and a traction member extending between the compress spindle and the anchor plug, the traction member being configured to apply compressive force along a longitudinal axis defined between the compress spindle and the anchor plug, wherein the traction member is further configured to bend to permit relative movement between the compress spindle and the anchor plug in a direction transverse to the longitudinal axis.

2. The bone attachment assembly of claim 1 , wherein the interface surface of the compress spindle defines one or more anti-rotation features configured to inhibit rotational displacement of the bone portion relative to the compress spindle.

3. The bone attachment assembly of claim 2, wherein the anti-rotation features comprise a plurality of chocks projecting from the interface surface.

4. The bone attachment assembly of claim 2, wherein the anti-rotation features comprise a plurality of longitudinal spikes extending from the interface surface along the longitudinal axis.

5. The bone attachment assembly of claim 4, wherein the longitudinal spikes are embedded in a compressible polymeric medium provided on the interface surface, such that compression of the medium exposes tips of the spikes.

6. The bone attachment assembly of claim 4, wherein the longitudinal spikes protrude directly from the interface surface without an intervening polymeric medium.

7. The bone attachment assembly of claim 2, wherein the anti-rotation features are configured to engage cancellous bone to reduce or eliminate relative rotation under load.

8. The bone attachment assembly of claim 1 , wherein the traction member comprises a flexible cable.

9. The bone attachment assembly of claim 8, wherein the anchor plug defines a cable connector interfacing a distal end of the cable.

10. The bone attachment assembly of claim 8, wherein the traction member comprises a traction bar comprising a cable connector interfacing a proximal end of the cable.1 1 . The bone attachment assembly of claim 10, wherein the compress spindle defines a channel slidably engaging the cable connector in the axial direction.

12. The bone attachment assembly of claim 8, wherein the cable comprises braided wire.

13. The bone attachment assembly of claim 12, wherein the cable comprises nitinol.

14. The bone attachment assembly of claim 1 , wherein the compress spindle defines an elongate centering post extending in the axial direction from the interface surface.

15. The bone attachment assembly of claim 14, wherein the centering post defines a uniform longitudinal profile.

16. The bone attachment assembly of claim 15, wherein the uniform longitudinal profile is conical.

17. The bone attachment assembly of claim 15, wherein the uniform longitudinal profile is cylindrical.

18. The bone attachment assembly of claim 14, wherein the centering post comprises a smooth surface.

19. The bone attachment assembly of claim 18, wherein the centering post is polished.

20. The bone attachment assembly of claim 18, wherein the centering post slidably contains a cable connector of the traction member.21 . The bone attachment assembly of claim 18, wherein a cable connector of the traction member extends beyond the centering post.

22. A method of implanting a bone attachment assembly, the method comprising: providing a bone attachment assembly comprising a compress spindle having an interface surface configured to engage a resected end of a bone portion, an anchor plug configured for securement in an intramedullary canal of the bone portion, and a traction member extending between the compress spindle and the anchor plug, the traction member being configured to apply compressive force along a longitudinal axis defined between the compress spindle and the anchor plug, wherein the traction member is further configured to bend to permit relative movement between the compress spindle and the anchor plug in a direction transverse to the longitudinal axis; preparing the resected end of the bone portion; inserting the anchor plug into the intramedullary canal of the bone portion; andapplying tension through the traction member to draw the compress spindle into compressive engagement with the resected end of the bone portion.

23. The method of claim 22, wherein the compress spindle is inserted such that a centering post extends into the intramedullary canal to stabilise the spindle against bending.

24. The method of claim 23, wherein the anchor plug is fixed to the bone portion using one or more transverse cortical pins or screws extending through apertures defined in the anchor plug.

25. The method of claim 24, wherein the traction member is tensioned by rotating a nut engaged with a threaded portion of a traction bar received within the compress spindle.

26. The method of claim 25, wherein the traction member comprises a flexible cable having a proximal end interfaced with the compress spindle and a distal end interfaced with the anchor plug.

27. A system comprising: a bone portion having a resected end and an intramedullary canal; and a bone attachment assembly comprising a compress spindle having an interface surface in compressive contact with the resected end of the bone portion, an anchor plug secured within the intramedullary canal of the bone portion, and a traction member extending between the compress spindle and the anchor plug, wherein the traction member is configured to apply compressive force along a longitudinal axis defined between the compress spindle and the anchor plug, and is further configured to bend to permit relative movement between the compress spindle and the anchor plug in a direction transverse to the longitudinal axis.

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