Artificial thighbone component

Abstract

The artificial femoral component has a stem and a neck. The neck defines a center of rotation when engaging a head that undergoes articular movement within the acetabular cup during use. The component has an anterior offset such that the center of rotation is offset anteriorly with respect to the longitudinal axis of the stem. The proximal portion of the neck has a posterior angle. This three-dimensional geometric shape, including the longitudinal section, increases the range of motion and reduces impingement.

Description

Technical Field

[0001] The present invention generally relates to hip arthroplasty. More specifically, the present invention relates to a type of femoral component.

Background Art

[0002] The femoral component has a stem that is inserted into the femoral canal during total hip arthroplasty, and the stem defines a neck that engages a head that articulates within a corresponding acetabular cup component.

[0003] The femoral component may be implanted with or without cement and sized according to anatomical considerations. Additionally, the femoral component is typically sized according to lateral and vertical offsets in the frontal plane that result in an offset between the native femur and pelvis.

[0004] These lateral and vertical offsets are typically determined from an A-P radiograph and are selected to accommodate, maintain, and restore the patient's native bone geometry to allow for sufficient range of motion, stability, and minimal bone impingement.

[0005] These femoral stem components are typically bilaterally interchangeable (i.e., not left- or right-specific and symmetric with respect to the frontal plane), which allows for inventory reduction.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention seeks to provide a femoral component that overcomes or substantially improves at least some of the drawbacks of the prior art, or at least provides an alternative.

[0007] If any prior art information is mentioned in this specification, it is understood that such mention does not constitute an admission that the information forms part of the common general knowledge in the art in Australia or any other country.

Means for Solving the Problem

[0008] Provided herein is an artificial femoral component having a three-dimensional geometric shape including a longitudinal section that increases the range of motion and reduces impingement.

[0009] The artificial femoral component of the present invention includes a stem and a neck. The neck defines a center of rotation when engaging a head that articulates within the acetabular cup during use.

[0010] The component has an anterior offset such that the center of rotation is offset anteriorly with respect to the longitudinal axis defined by the stem. The anterior offset generally increases the anterior range of motion to the anterior bone impingement that typically occurs when the femoral groove impacts the anterior inferior iliac spine (AIIS) of the pelvis during full flexion. In this scenario, the anterior offset positions the femoral groove further away from the AIIS during full flexion, thereby increasing the anterior range of motion until bone impingement occurs, unless a distal impingement such as the knee hitting the chest occurs or further movement is prevented by posterior soft tissue restraint. However, such an anterior offset increases the likelihood of posterior implant impingement, where the neck impacts the posterior rim of the acetabular cup.

[0011] Accordingly, the proximal portion of the neck has a posterior angle. The posterior angle increases the posterior range of motion to the posterior implant impingement. The proximal and distal portions of the neck described herein are described in relation to the insertion direction of the component, and thus, by general convention, the proximal portion of the neck is towards the patient's head and the distal portion of the neck is towards the patient's feet.

[0012] The anterior offset can be defined by the anterior translation and / or angle of the neck relative to the stem.

[0013] For example, the anterior angle can be from 5° to 20°, and in one embodiment can be approximately 15°. Further, the posterior angle can be from 10° to 30°, approximately 23°. Due to the net effect of the anterior offset and the posterior angle, the center of rotation can be offset 3 to 10 mm anteriorly, and in one embodiment approximately 6 mm, from the frontal plane that coincides with the longitudinal axis of the stem.

[0014] The component can be designed according to the size of the acetabular cup such that the posterior angle transition point generally coincides with the rim of the acetabular cup component, thereby maximizing the posterior range of motion.

[0015] At least one portion along the neck can have a cross-section with a flattened or small posterior superior surface. For example, the cross-section can define an ellipse having a major axis and a minor axis, and the major axis can define the angle of rotation relative to the longitudinal axis of the stem in the longitudinal section. The angle of rotation is greater than 10°, and further, in some embodiments can be approximately 30°.

[0016] The small posterior superior surface increases the posterior range of motion during full flexion of the hip joint. Usually, anterior bone impingement occurs before anterior prosthetic impingement, thus preventing anterior prosthetic impingement. In other words, even if there is a possibility of anterior prosthetic impingement or even if it has occurred, the small posterior superior surface increases the range of motion by increasing the distance between the rim of the acetabular cup and the side of the neck. Also, the small posterior superior surface presents a flatter side of the neck relative to the rim of the cup, reducing point impingement, thereby reducing the possibility of mechanical failure of the rim of the acetabular component or the neck. The instability caused by impingement is also thereby reduced or avoided.

[0017] In some embodiments, the twist angle may increase (i.e., rifling) from the distal end of the neck towards the proximal end of the neck. The neck may be configured such that the twist angle increases to a maximum twist angle at a position of the neck generally corresponding to the rim of the cup.

[0018] Rifling of the elliptical axis of the neck is beneficial in relation to posterior impingement during extension and anterior impingement during flexion.

[0019] Furthermore, the major axis of the ellipse is beneficially oriented to withstand the heel strike load of the ground reaction force, which varies but is maximized when the hip joint is flexed approximately 30° during walking.

[0020] According to one aspect, a femoral component comprising a stem and a neck is provided, the neck defining a center of rotation when engaging a head that articulates within a acetabular cup during use, the component having an anterior offset such that the center of rotation can be offset anteriorly with respect to the longitudinal axis of the stem, and the distal portion of the neck having a posterior angle.

[0021] The distal portion of the neck may form a trunnion that engages a socket of the head.

[0022] The anterior offset is defined above the junction of the neck and the stem (i.e., above the osteotomy line), thereby avoiding modification of the stem itself and thus standardizing the instrument and orthopedic procedure.

[0023] The component may be configured such that the junction generally coincides with the osteotomy surface when implanted during use.

[0024] The anterior offset may be defined by an anterior translation between the neck and the stem. The anterior translation may exceed 2 mm.

[0025] The anterior offset may be defined by an anterior angle of the neck with respect to the stem.

[0026] The anterior angle can be defined between the longitudinal axis of the proximal part of the neck and the frontal plane that coincides with the longitudinal axis of the stem. On the osteotomy surface, the anterior angle can be 3° to 25°. On the osteotomy surface, the anterior angle can be approximately 15°.

[0027] The posterior angle can be defined between the longitudinal axis of the distal part of the neck and the longitudinal axis of the proximal part of the neck. The posterior angle can be 10° to 30°. The posterior angle can be approximately 23°.

[0028] The center of rotation can be offset 3 to 10 mm anteriorly from the frontal plane that coincides with the longitudinal axis of the stem. The center of rotation can be offset approximately 6 mm anteriorly from the frontal plane that coincides with the longitudinal axis of the stem.

[0029] The angle defined by the longitudinal axis of the distal end of the neck and the frontal plane defined by the longitudinal axis of the stem can be 5 to 20°. The angle defined by the longitudinal axis of the distal end of the neck and the frontal plane defined by the longitudinal axis of the stem can be approximately 8°.

[0030] The neck can define a posterior angle transition point between its distal and proximal parts. The transition point can generally coincide with the rim of the acetabular cup during use. The transition point can be more than half away along the neck from the distal end of the neck. The transition point can be approximately two-thirds along the neck from the distal end of the neck.

[0031] At least one portion along the neck can have a cross-section with a small posterior superior face. The cross-section defines a major axis and a minor axis, and the major axis can define the angle of rotation with respect to the longitudinal axis of the stem in the longitudinal section. The cross-section can be elliptical. The angle of rotation can be greater than 10°. The angle of rotation can be greater than 15°. The angle of rotation can be approximately 30°.

[0032] The angle of rotation can increase along the neck from the distal end of the neck. The angle of rotation increases along the neck to the maximum angle of rotation. The position of the maximum angle of rotation can generally coincide with the position where the neck collides with the rim of the cup during use.

[0033] The component further comprises an additional femoral component, which may be symmetric with the femoral component in a longitudinal section.

[0034] According to another aspect, there is provided a hip arthroplasty regarding the artificial femoral component described herein, including implanting a component between the original femur and pelvis such that the center of rotation defined by the neck is offset forward with respect to the longitudinal axis of the stem when engaging a head that articulates within the acetabular cup, and the proximal portion of the neck may have a posterior angle.

[0035] According to another aspect, there is provided an artificial femoral component comprising a stem and a neck, the neck having a cross-section with a small posterior superior surface.

[0036] The cross-section defines a major axis and a minor axis, and the major axis defines the angle of rotation with respect to the longitudinal axis of the stem in a longitudinal section.

[0037] The cross-section may be elliptical.

[0038] The angle of rotation may be greater than 10°. The angle of rotation may be greater than 15°. The angle of rotation may be approximately 30°.

[0039] The angle of rotation may increase along the neck from the distal end of the neck.

[0040] The angle of rotation may increase along the neck to a maximum angle of rotation. The position of the maximum angle of rotation may generally coincide with the position where the neck collides with the rim of the cup during use.

[0041] Other aspects of the present invention are also disclosed.

[0042] Despite any other forms that may be included within the scope of the present invention, the preferred embodiments of the present disclosure are described herein by way of example only with reference to the accompanying drawings.

Brief Description of the Drawings

[0043]

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Embodiments for Carrying Out the Invention

[0044] FIG. 1 shows an artificial femoral component 100 including a stem 101 and a neck 102.

[0045] During total hip arthroplasty, the stem 101 is inserted into the femoral canal with or without cement, and the neck 102 protruding from the stem 101 engages with a head 105 that articulates within an acetabular cup 106 in the manner shown in FIGS. 17 and 18.

[0046] The component 100 has a left and a right side, and the figure shows the left version of the component 100 (except for FIG. 13 showing the symmetric right version of the component 100).

[0047] FIG. 2 shows the neck 102 that defines a center of rotation 104 when engaging with the head 105 that articulates within the acetabular cup 106.

[0048] The component 100 has an anterior offset such that the center of rotation 104 is offset anteriorly (shown as 116 in FIG. 2) with respect to the longitudinal axis 129 defined by the stem 101.

[0049] The anterior offset increases the anterior range of motion to the anterior bone impingement. The anterior bone impingement can occur when the femoral groove collides with the anterior inferior iliac spine (AIIS) of the pelvis during full flexion. In this scenario, due to the anterior offset, the femoral groove is positioned further away from the AIIS during full flexion, thereby increasing the anterior range of motion until bone impingement occurs.

[0050] Furthermore, the proximal portion 107 of the neck 102 has a posterior angle 108 to increase the posterior range of motion until posterior implant impingement occurs. The posterior angle 108 counteracts the reduction in the posterior rotation range to the implant impingement caused by the anterior offset.

[0051] The proximal portion 107 can form and include a trunnion 109 that engages with the socket of the head 105.

[0052] Generally speaking, referring to FIG. 2, the posterior angle 108 can be defined by the orientation of the longitudinal axis of the proximal portion 107 of the neck (ordinarily defining the trunnion 109) with respect to the frontal plane defined by the longitudinal axis 129 of the stem 101.

[0053] FIGS. 3 and 5 are comparisons of scenarios regarding a 40 / 20 cup in hyperextension, showing an exemplary external rotation of approximately 113° of a conventional stem 110 (symmetric with respect to the frontal plane) versus an external rotation of approximately 125° of the stem 101 of the present invention.

[0054] FIG. 2 shows the component 100 generally along the osteotomy plane 103 shown in FIG. 9.

[0055] The anterior offset can be provided in various ways including a forward translation or an angle at the upper portion of the stem 101. Even if the stem 101 has an anterior angle, the stem 101 still defines a main longitudinal axis 129.

[0056] However, in a preferred embodiment, the anterior offset is defined by the neck 102 above the junction of the neck 102 and the stem 101. In other words, the anterior offset can be defined completely above the osteotomy plane 103.

[0057] As shown in FIG. 2, the anterior offset can be defined by a neck 102 having an anterior translation 111 relative to the stem 101. More particularly, the distal end 113 of the longitudinal axis 112 of the distal portion 114 of the neck 102 can be offset relative to the frontal plane defined by the longitudinal axis 129.

[0058] In the embodiment shown in FIG. 2, the anterior translation 111 can be approximately 4 mm.

[0059] The anterior offset can be defined by a neck 102 having an anterior angle relative to the frontal plane defined by the longitudinal axis 129 of the stem 101.

[0060] From this perspective, the distal portion 114 of the neck 102 can form an angle of 5° to 20° anteriorly (such as at the height of the osteotomy) relative to the frontal plane defined by the longitudinal axis 129 of the stem 101. In one embodiment, the distal portion 114 of the neck 102 can form an angle of approximately 15° anteriorly relative to the frontal plane that coincides with the longitudinal axis of the stem 101.

[0061] From the perspective of the osteotomy plane shown in FIG. 2, the posterior angle 108 can be defined between the longitudinal axis 112 of the distal portion 114 of the neck 102 and the longitudinal axis 115 of the proximal portion 107 of the neck 102. From this perspective, the posterior angle 108 can be 10 to 30°, and in one embodiment, approximately 23°.

[0062] Due to the net offset of the anterior offset and the posterior angle of the neck 102, the center of rotation 104 has an anterior offset 116 of 4 to 10 mm, and in some embodiments, approximately 6 mm, from the frontal plane that coincides with the longitudinal axis 129.

[0063] Furthermore, the net angle 127 between the forward angle (defined by the longitudinal axis 112 of the distal portion 114 of the neck 102) and the rearward angle (defined by the longitudinal axis 115 of the proximal portion 107 of the neck 102) can result in a net rearward angle (i.e., the angle defined by the longitudinal axis 115 of the proximal portion 107 of the neck 102 and the frontal plane 128 defined by the longitudinal axis 129 of the stem 101) of 5 to 20°, and in some embodiments approximately 8°.

[0064] The neck 102 can generally define a rearward angle transition point 117 between the proximal portion 107 and the distal portion 114. The position of the transition point 117 preferably generally coincides with the position of the rim 124 of the acetabular cup 106. Thus, the location of the transition point 117 can be defined according to the size of the acetabular cup 106.

[0065] The transition point 117 can be located more than halfway along the neck 102 from the distal end of the neck 102. The transition point 117 can be located approximately two-thirds along the length of the neck 102 from the distal end of the neck 102.

[0066] As shown in FIG. 2, the neck 102 can form a smooth curve (i.e., a curve without a sharp lateral transition) with respect to the transition point 117.

[0067] In some embodiments, at least one portion along the neck 102 can have a cross-section 120 with a small posterior superior surface to further increase the posterior range of motion of the hip joint at full flexion of the hip joint to posterior superior impingement against the rim 124 of the cup 106. In other words, even if anterior hip impingement may occur or has occurred, the small posterior superior surface increases the range of motion by increasing the distance between the rim 124 of the acetabular cup 106 and the side of the neck 102. Also, the small posterior superior surface reduces the point contact load against the rim 124 of the cup 106 that can cause stress or fracture of the neck 102, damage to the cup 106, or instability (separation of the femoral head 105 and the cup 106).

[0068] In the embodiment shown in FIG. 14, the cross-section 120 defines a major axis 121 and a minor axis 122, and the major axis 121 defines a swivel angle 126 with respect to the longitudinal axis 129 of the stem 101. The swivel angle 126 is preferably greater than 10°. In the illustrated embodiment, the swivel angle 126 is approximately 30°.

[0069] FIG. 17 shows a typical cross-section 119 of a conventional neck 118, and the major axis 121 is usually aligned along the longitudinal axis 129 of the stem 101 to enhance its strength when upright. As can be seen from FIG. 17, the cross-section 119 has a relatively sharp edge 123, which increases the point load on the rim 124 of the acetabular cup 106 in the event of a posterior implant impingement. As suggested above, this point load can cause stress or fracture of the neck 118, or damage to the cup 106.

[0070] However, FIG. 18 shows the effect of the major axis angle of the neck 102 of the present invention, which not only increases the posterior swivel range to cup impingement, but also makes the side of the neck 102 flatter with respect to the rim 124 of the acetabular cup 106, thereby reducing the point load stress of the neck 102 and the instability caused by impingement.

[0071] In the preferred embodiment shown, the cross-section 120 is elliptical.

[0072] FIG. 15 shows the cross-section 120 at the impingement position 125 along the neck 102. The impingement position 125 is generally the position of the neck 102 that collides with the rim 124 of the cup 106.

[0073] The impingement position 125 is preferably selected to coincide with the position of the rim 124 of the acetabular cup 106 to maximize its avoidance and provide a flatter side.

[0074] The impingement position 125 may coincide with the aforementioned posterior angle transition point 117.

[0075]

[0075] In some embodiments, the twist angle 126 increases (i.e., spirals or rifling) towards the proximal portion 107 of the neck 102. For example, at the distal end of the neck 102, the twist angle 126 is 0°, and the twist angle 126 increases towards the distal end of the neck 102.

[0076]

[0076] Preferably, the neck 102 is configured such that the twist angle 126 increases towards the impingement position 125. In other words, the twist angle 126 can increase from 0° at the distal end of the neck 102 to 30° at the impingement position 125.

[0077] It should be noted that the aforementioned small posterior superior aspect can be applied to the neck of a conventional implant (i.e., symmetric in the longitudinal section) to increase the posterior mobility to the posterior implant impingement.

[0078] In the above description, for purposes of explanation, specific nomenclature has been used to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that specific details are not required to practice the present invention. Accordingly, the above description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed, and many modifications and variations are possible in light of the above teachings. Some embodiments have been selected and described in order to best explain the principles of the invention and its practical application, thereby enabling those skilled in the art to best utilize the invention and various embodiments with various modifications suitable for the particular use contemplated. The following claims and their equivalents are intended to define the scope of the present invention.

Claims

Claim 1 An artificial femoral component comprising a stem and a neck, said neck defining a center of rotation when engaging a head that articulates within an acetabular cup during use, said component having a forward offset such that the center of rotation is offset forward relative to the longitudinal axis of the stem, the proximal portion of said neck having a posterior angle, component. Claim 2 The component according to claim 1, wherein the proximal portion of said neck forms a trunnion that engages a socket of the head. Claim 3 The component according to claim 1, wherein the forward offset is defined above the junction of the neck and the stem. Claim 4 The component according to claim 3, wherein the component is configured such that the junction generally coincides with the bone cut surface when implanted during use. Claim 5 The component according to claim 1, wherein the forward offset is defined by a forward translation between the neck and the stem. Claim 6 The component according to claim 5, wherein the forward translation exceeds 2 mm. Claim 7 The component according to claim 1, wherein the forward offset is defined by a forward angle of the neck relative to the stem. Claim 8 The component according to claim 7, wherein the forward angle is defined between the longitudinal axis of the proximal portion of the neck and a frontal plane that coincides with the longitudinal axis of the stem. Claim 9 The component according to claim 8, wherein the forward angle is 3° to 25° at the bone cut surface. Claim 10 The component according to claim 8, wherein the forward angle is approximately 15° at the bone cut surface. Claim 11 The component according to claim 1, wherein the posterior angle is defined between the longitudinal axis of the distal portion of the neck and the longitudinal axis of the proximal portion of the neck. Claim 12 The component according to claim 11, wherein the posterior angle is 10° to 30° at the bone cut surface. Claim 13 The component according to claim 11, wherein the posterior angle is approximately 23° at the bone cut surface. Claim 14 The component according to claim 1, wherein the center of rotation is offset 3 to 10 mm forward from a frontal plane that coincides with the longitudinal axis of the stem. Claim 15 The component according to claim 1, wherein the center of rotation is offset approximately 6 mm forward from a frontal plane that coincides with the longitudinal axis of the stem. Claim 16 The angle defined by the longitudinal axis of the distal end of the neck and the frontal plane defined by the longitudinal axis of the stem is 5 to 20°, the component according to claim 1.

17. The angle defined by the longitudinal axis of the distal end of the neck and the frontal plane defined by the longitudinal axis of the stem is approximately 8°, the component according to claim 1.

18. The neck defines a posterior angle transition point between its distal and proximal portions, the component according to claim 1.

19. The transition point generally coincides with the rim of the acetabular cup during use, the component according to claim 18.

20. The transition point is located more than half away along the neck from the distal end of the neck, the component according to claim 18.

21. The transition point is located approximately two-thirds along the neck from the distal end of the neck, the component according to claim 18.

22. At least one portion along the neck has a cross-section with a small posterior upper surface, the component according to claim 1.

23. The cross-section defines a major axis and a minor axis, and the major axis defines a rotation angle with respect to the longitudinal axis of the stem in the longitudinal section, the component according to claim 22.

24. The cross-section is elliptical, the component according to claim 23.

25. The rotation angle is greater than 10°, the component according to claim 23.

26. The rotation angle is greater than 15°, the component according to claim 23.

27. The rotation angle is approximately 30°, the component according to claim 23.

28. The rotation angle increases along the neck from the distal end of the neck, the component according to claim 23.

29. The rotation angle increases along the neck to a maximum rotation angle, the component according to claim 28.

30. The position of the maximum rotation angle generally coincides with the position where the neck collides with the rim of the cup during use, the component according to claim 29.

31. Further comprising a further femoral component, and the further femoral component is symmetric with the femoral component in the longitudinal section, the component according to claim 1.

32. A hip arthroplasty related to the artificial femoral component according to claim 1, wherein when engaging with a head that articulates within the acetabular cup, the center of rotation defined by the neck is offset forward with respect to the longitudinal axis of the stem, and the proximal portion of the neck has a posterior angle, and includes implanting the component between the original femur and the pelvis.

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