Dual mobility hip prosthesis

Abstract

The dual-mobility bearing component of the present invention has a geometry featuring an opening with high sides and low ends that aims to reduce complications associated with conventional dual-mobility prostheses by minimizing torque, shear stress, and cross-shear and wear through compartmentalization of motion between the medial and lateral bearings. This geometry directs flexion-extension motion of the femoral component to occur primarily along the wider axis of the opening, while adduction-abduction motion occurs primarily along a relatively narrower axis, with adduction-abduction motion typically restricted to the lateral bearing surface of the bearing component and induced by impingement of the neck of the femoral component against the high side of the rim along the narrower axis.

Description

[Technical Field]

[0001] The present invention relates generally to a type of bearing component for a dual mobility hip prosthesis. [Background technology]

[0002] Total hip arthroplasty is a highly successful procedure that involves the insertion of prosthetic components into and for the repair of a diseased hip joint.

[0003] The components include a stem for the femoral component and a socket for the acetabular component. These two sides of the joint articulate via a bearing component. The bearing typically has a head on the femoral side and a liner on the acetabular side.

[0004] When the neck of the femoral component and the rim of the acetabular component come into contact, cervical-acetabular prosthetic impingement is said to occur. Prosthetic impingement is highly detrimental because it can lead to component wear, damage, instability, and failure. These complications often lead to extensive further surgical intervention (revision).

[0005] To avoid prosthetic impingement, hip replacements can be designed with a much higher head-to-neck diameter ratio than is the case for natural hip joints. Ideally, bone geometry and soft tissue tension would prevent excessive range of motion or limit movement before prosthetic impingement can occur. However, prosthetic impingement and other problems still occur.

[0006] Dual mobility prostheses involve the inclusion of additional and intermediate dual mobility bearing components. The effect of the dual mobility bearing components is to improve (i.e., increase) the effective head-neck diameter ratio, thereby further avoiding prosthetic impingement. Dual mobility bearing components are typically made from high density polyethylene (HDPE).

[0007] Dual-mobility prostheses were originally developed in France and were intended for use only in elderly patients. However, due to their success, their use has increased in recent years in many countries and among younger patients to further improve the results of total hip arthroplasty.

[0008] The dual-mobility bearing component surrounds the femoral head in cross section at an angle greater than 180°, thereby locking the head and allowing it to articulate in the dual-mobility bearing component at a medial bearing. The dual-mobility bearing component is then seated or passively reduced in an acetabular liner component, where it can also rotate in a lateral bearing. Torque stresses occur in both the medial and lateral bearings (whether or not either bearing is moving).

[0009] However, due to differences in friction torque (resulting from the different radii), most of the motion occurs in the medial bearing. When the prosthetic femoral neck abuts the rim of the dual-mobility bearing component (i.e., the medial bearing), the lateral bearing only moves passively. Also, the primary motion occurring in the medial bearing is rotation.

[0010] These motions and torque stresses in multiple directions cause more frictional wear in HDPE than if these stresses were aligned. This so-called "cross shear" is particularly detrimental to HDPE in terms of (frictional) wear. Polyethylene wear is a well-known problem in conventional hip replacements with dual-mobility bearing components.

[0011] The present invention seeks to provide a method that overcomes or substantially ameliorates at least some of the deficiencies of the prior art, or at least to provide an alternative.

[0012] Where any information of the prior art is referred to herein, it should be understood that 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 Invention

[0013] Although dual-mobility prostheses have been successful in improving head-neck diameter ratios, several complications have arisen that are unique to their use. Furthermore, the expansion of dual-mobility prostheses to younger, more active patients than originally intended has led to an increased incidence of these complications.

[0014] Provided herein is an HDPE (or any other suitable material) dual-mobility bearing component designed to reduce many of these complications. It is contemplated that the dual-mobility bearing component of the present invention is suitable for safe use in younger, more active patients, rather than being limited to use in elderly patients as originally intended.

[0015] The dual mobility bearing component of the present invention has a unique shape compared to conventional dual mobility bearing components in that it has a higher side opening and a lower end height. The end height may be similar to the height of a typical component, but the effect of the higher sides is to partially encase the head more than a typical dual mobility bearing component.

[0016] Specifically, rather than looking like a conventional 3 / 4 spherical cap with a circular opening, the dual mobility bearing component of the present invention has a "football stadium-like" or "clamshell-like" appearance and shape with high side walls and low end walls.

[0017] It is therefore envisioned that torque, shear stress and motion in the inner and outer bearings are substantially compartmentalized, resulting in substantially reduced cross shear and cross shear induced wear.

[0018] Specifically, the geometry of the present invention induces flexion-extension torque moments and motion to occur primarily at the medial bearing (along with rotation), while abduction-adduction motion is induced to occur primarily at the lateral bearing due to impingement of the prosthesis neck along the sideline or high wall of the dual-mobility bearing component.

[0019] In this way, the two components of cross shear are stratified or separated to occur at the inner and outer bearings, respectively.

[0020] The rim may have an inner flat contact surface so that engagement at the intermediate bearing occurs between two parallel edges and surfaces of the neck and dual mobility bearing component, respectively.

[0021] Thus, as the prosthesis neck moves the outer bearing, contact stresses are relieved at the middle bearing and torque loads at the inner bearing are significantly reduced.

[0022] Furthermore, the shape of the dual mobility bearing component of the present invention results in an opening that is oval in plan view rather than circular. Thus, the non-circular plan cross section and non-coplanar inner edge of the rim of the dual mobility bearing component of the present invention flares out to reduce the insertion force required to stretch the dual mobility bearing component onto the head during insertion.

[0023] This configuration also increases the extraction force required to remove the head from the dual-mobility bearing component. Stated another way, the dual-mobility bearing component of the present invention may be more securely secured to the head to prevent dissociation (which, by definition, is a failure requiring revision surgery). Furthermore, the required displacement the head must travel to cause dissociation is increased with the present design compared to that of a typical dual-mobility bearing component.

[0024] Other aspects of the invention are also disclosed.

[0025] While any other form may be considered which may fall within the scope of the invention, preferred embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 illustrates a perspective view of a dual mobility bearing component according to one embodiment. [Figure 2] 10 illustrates a dual mobility bearing component according to a further embodiment. [Figure 3] 2 illustrates insertion of the head of the femoral component into the dual mobility bearing component of FIG. 1; [Figure 4] A cross-sectional view of FIG. [Figure 5] 2 illustrates articulation of the head of the femoral component within the dual mobility bearing component of FIG. 1; [Figure 6] FIG. 6 is a cross-sectional view of FIG. 5. [Figure 7] FIG. 1 shows a plan view of a dual mobility bearing component. [Figure 8] FIG. 1 shows a cross-sectional side view of a dual mobility bearing component. [Figure 9] FIG. 1 shows a cross-sectional perspective view of a dual mobility bearing component. [Figure 10] 1 shows an enlarged cross-sectional view of a rim of a dual mobility bearing component. [Figure 11] 3 shows an enlarged view of the rim of the dual-mobility bearing component of FIG. 2; [Figure 12] 10 shows a comparison of insertion and extraction forces of a dual mobility bearing component of the present invention compared to a conventional dual mobility bearing component. [Figure 13-18] 1A-C show various embodiments of the dual mobility bearing component of the present invention, with sub-figure A being a cross-sectional side view along the major axis, sub-figure B being a cross-sectional side view along the minor axis, and sub-figure C being a perspective view. DETAILED DESCRIPTION OF THE INVENTION

[0027] Provided herein is a hip prosthesis comprising an acetabular component defining a hemispherical medial bearing surface and a femoral component 104 having a head 103 defining a hemispherical lateral bearing surface.

[0028] The acetabular component may comprise a bone-bonded metal or other cup lined with a highly polished liner or surface.

[0029] The femoral component 104 may define a neck 105 having a proximal trunnion 106 configured for a mortise interlock or similar mechanism within a blind opening 107 defined by the head 103. The head 103 is typically metal or ceramic, and the neck 105 is typically metal.

[0030] The prosthesis further comprises a dual mobility bearing component 100 defining a hemispherical lateral bearing surface 101 that freely articulates within the acetabular component to define a lateral bearing.

[0031] The dual mobility bearing component 100 further defines a hemispherical inner bearing surface 102, and the spherical head 103 is free to articulate within the inner bearing surface 102, thereby defining an inner bearing.

[0032] The bearing component 100 is typically a polymer component such as one comprising high density polyethylene (HDPE).

[0033] The bearing component 100 defines a rim 108 that transitions the bearing surfaces 101, 102, thereby defining an opening 109 (best seen in FIG. 7) for the head 103 and neck 105 of the femoral component 104.

[0034] The rim 108 has a 3D shape that can generally be described as having high sides and low ends, as if a sphere were cut by an ellipsoid. In other words, the rim 108 is higher at the sides compared to the ends.

[0035] More specifically, rim 108 defines a high side 111 that is transverse to a minor axis 113 (e.g., the relatively narrow axis of opening 109 according to the plan view shown in FIG. 7 ) and a low side 112 that is transverse to an orthogonal major axis 114 (e.g., the relatively wide axis of opening 109). In other words, with reference to FIG. 7 , opening 109 is wider along major axis 114 than it is along minor axis 113.

[0036] "Freely articulate" refers to the ability of the bearing component 100 or head 103 to move, rotate, or adjust without restraints (i.e., pins, coupling components, etc. that restrict movement) within the acetabular component or the inner bearing surface 102 of the bearing component 100, respectively, to accommodate different positions or orientations. That is, the bearing component 100 articulates freely within the acetabular component without mechanical restraints (pins, coupling components, etc.) that restrict movement of the bearing component 101 along its pivot axis relative to the acetabular component.

[0037] The term "semispherical" refers to bearing surface 101 or bearing surface 102 having a curved or rounded shape similar to that of a sphere, but which does not extend completely into a three-dimensional spherical shape, thereby being a partially spherical surface that allows for free articulation.

[0038] Thus, once implanted, the free articulation provided by the hemispherical bearing surfaces 101, 102 generally rotates and orients the bearing component 100 within the acetabular component such that flexion-extension movement of the femoral component 104 occurs primarily along the wider side of the major axis 114, while adduction-abduction movement of the femoral component 104 (induced to occur only in the lateral bearing component 100 by impaction of the neck 105 against the higher side of the rim 108 of the dual-mobility bearing component 100 (i.e., along the minor axis 113)) occurs primarily along the relatively narrower side of the minor axis 113.

[0039] The angular range of the lower end 112 can be similar to that of conventional dual mobility bearing components designed to capture the femoral head 103 at angles greater than 180°, such as approximately 240°, thereby capturing the femoral head 103 and preventing dislocation (commonly referred to as dissociation) from the dual mobility bearing component. For example, Figure 13B shows the angular range of the lower end 112 designed to capture the head 103 at approximately 260°, and Figure 17B shows the angular range of the lower end 112 designed to capture the head 103 at approximately 230°.

[0040] However, the high side 112 of the bearing component 100 is designed to capture the head 103 at an angle greater than that of conventional dual mobility liners, for example, greater than 270°, preferably greater than 280°, and in embodiments greater than 300°.

[0041] The effect of the capture of head 103 by high side 111 is that, in one embodiment, low end 112 may capture head 103 at less than 180°, as shown in the embodiment of Figure 18B.

[0042] As shown in FIGS. 13-18A, the rim 108 may define a parabolic cross-section along the major axis 114.

[0043] The embodiment of Figures 13-18 shows a standard size 28 / 44 bearing component 100, meaning that the bearing component 100 has an outer diameter of approximately 44 mm and an inner diameter of approximately 28 mm. The relevant dimensions shown in parentheses in each figure represent the width of the opening 109 along the minor axis 113 and the length of the opening 109 along the major axis 114. For example, according to the embodiment of Figure 13, the opening 109 is 16 mm wide and 27 mm long.

[0044] In embodiments, the outer diameter of the bearing component 100 may be configured to fit into an acetabular cup having an inner diameter of 38 mm to 62 mm. Additionally, the inner diameter of the bearing component 100 may have diameters including 22 mm, 28 mm, 32 mm, and 36 mm.

[0045] According to the illustrated embodiment, the opening 109 may have a length of 25 mm to 27 mm and a width of approximately 16 mm to 19 mm, depending on the angular extent of the high side 111 and low side 112 .

[0046] The rim 108 may define an inner flat contact surface 115 designed to flatly contact the neck 105 of the femoral component 104 to distribute and minimize contact forces thereover.

[0047] With reference to the various embodiments shown in Figures 13-18, the angle of the arc defined by the inner flat contact surface 115 can be between approximately 21° and 53° along the minor axis 113 and approximately 97° to 187° along the major axis 114.

[0048] 10, the rim 105 may define a rounded shoulder 116 connecting the inner flat contact surface 115 and the outer bearing surface 101. As further shown in FIG. 10, the rim 108 may define a chamfered inner edge 117, approximately 1 mm to 3 mm wide, connecting the inner flat contact surface 115 and the inner bearing surface 102.

[0049] 11, the rim 108 may define expansion slits 118 that traverse the outer bearing surface 101, the inner flat contact surface 115, and the inner bearing surface 102 along the minor axis 113. These expansion slits 118 allow the rim 108 to expand as the head 103 presses over the chamfered edge 117 during insertion.

[0050] Each expansion slit 118 may terminate in one or more blind holes 119 that may inhibit potential polymer crack propagation. The upper blind holes 119 shown in FIG. 11 may be inserted beyond a flat portion of the contact surface 108, such as through a rounded shoulder 116 or the outer bearing surface 101. In an embodiment, each expansion slit 118 may terminate in a lower blind hole in the inner bearing surface 102.

[0051] In a further embodiment, the rim 108 defines a locating dimple (not shown) for seating and positioning the femoral head 103 prior to insertion. The bearing component 100 may include a pair of locating dimples approximately midway along the minor axis 113 of the flat contact surface 115.

[0052] FIG. 12 shows a comparison 120 of the insertion and extraction forces of the bearing component 100 of the present invention compared to a conventional liner with a flush rim.

[0053] The comparison 120 is shown with force along the vertical axis and displacement along the horizontal axis.

[0054] Comparison 120 shows an insertion force 120 applied to press head 103 into bearing component 100 until head 103 is concentric with inner bearing surface 103 at concentric point 125, and an extraction force 122 to pull head 103 out of bearing component 100.

[0055] When the head 103 is inserted into the bearing component 100 of the present invention, the sides of the head 103 contact the high side 113 before contacting the low side 112, thereby distributing the insertion force 123 compared to the insertion force 124 of the conventional liner and exhibiting a lower maximum peak force 127 compared to the maximum peak force 126 of the conventional liner.

[0056] During pull-out 122, the greater encirclement of head 106 by tall sides 112 grips head 103 more effectively than a conventional liner does, thereby exhibiting a steeper pull-out force 129 with a greater maximum peak force 128 compared to the maximum peak force 130 of the pull-out force 131 of a conventional liner. Additionally, the greater encirclement of head 106 by tall sides 112 increases the displacement required for pull-out or disengagement to occur.

[0057] The foregoing description, for purposes of explanation, uses specific terminology to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that specific details are not required to practice the present invention. Thus, the foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, as many modifications and variations are apparent in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, so that others skilled in the art can best utilize various embodiments with various modifications suited to the invention and the particular uses contemplated. It is intended that the following claims and their equivalents define the scope of the invention.

Claims

1. 1. A hip joint prosthesis, comprising: an acetabular component defining a hemispherical medial bearing surface; a femoral component having a head defining a hemispherical outer bearing surface; 1. A dual mobility bearing component, comprising: a hemispherical lateral bearing surface that freely articulates within said acetabular component to define a lateral bearing; a hemispherical inner bearing surface within which the head freely articulates to define an inner bearing; and a rim transitioning the bearing surface and defining an opening for a head of the femoral component, a rim having a higher side compared to an end; a dual-mobility bearing component defining A hip joint prosthesis comprising:

2. 2. The prosthesis of claim 1, wherein the hemispherical bearing surface, once implanted, orients the bearing component within the acetabular component so that flexion-extension movement of the femoral component occurs primarily along the wider axis of the opening and adduction-abduction movement of the femoral component occurs primarily along the relatively narrower axis of the opening.

3. 3. The prosthesis of claim 2, wherein adduction and abduction of the femoral component are induced to occur primarily at the lateral bearing component by impaction of the neck of the femoral component against the high side of the rim along the relatively narrow axis of the opening.

4. The prosthesis of claim 1 , wherein the high side of the rim is configured to capture the head at an angle greater than 270°.

5. The prosthesis of claim 1 , wherein the high side of the rim is configured to capture the head at an angle greater than 280°.

6. The prosthesis of claim 1 , wherein the high side of the rim is configured to capture the head at an angle greater than 300°.

7. The prosthesis of claim 1 , wherein the lower side of the rim is configured to capture the head at an angle less than 180°.

8. 10. The prosthesis of claim 1, wherein a high side of the rim intersects a minor axis and a low side of the rim intersects a major axis, the rim defining a parabolic cross section along the major axis.

9. The prosthesis of claim 1 , wherein the opening defines a cross-section having a length of about 24 mm to 28 mm and a width of about 16 mm to 22 mm.

10. The prosthesis of claim 1 , wherein the rim defines an inner flat contact surface configured to be parallel to an edge of a neck of a femoral component when contacted by the neck.

11. 11. The prosthesis of claim 10, wherein a high side of the rim intersects a minor axis and a low side of the rim intersects a major axis, and wherein the inner flat contact surface defines an arc angle of between about 21° and 53° across the minor axis and an arc angle of about 97° to 187° along the major axis.

12. The prosthesis of claim 10 , wherein the rim defines a rounded shoulder connecting the inner flat contact surface and the outer bearing surface.

13. The prosthesis of claim 10 , wherein the rim defines a chamfered edge connecting the inner flat contact surface and the inner bearing surface.

14. The prosthesis of claim 1 , wherein the rim has a slit through its high side.

15. 10. The prosthesis of claim 1, wherein the rim defines an inner flat contact surface, the rim having a slit in a higher side thereof that traverses the inner flat contact surface and the inner bearing surface.

16. 16. The prosthesis of claim 15, wherein each slit terminates in a blind hole.

17. The prosthesis of claim 15, wherein the upper blind hole extends beyond the inner flat contact surface.

18. The prosthesis of claim 1 , wherein the rim defines an inner contact surface, the rim having a positioning dimple in the inner contact surface on a higher side thereof.

19. The prosthesis of claim 1 , further comprising the femoral component, a head of the femoral component articulating against the medial bearing surface.

20. 20. The prosthesis of claim 19, further comprising an acetabular component, the lateral bearing surface articulating against the acetabular component.

21. 21. The prosthesis of claim 20, wherein the acetabular component includes an acetabular cup liner, the lateral bearing surface articulating against an medial bearing surface of the acetabular cup liner.

22. 22. The prosthesis of claim 21, wherein the acetabular cup liner is constrained with a locking ring.

23. 10. A method involving the prosthesis of claim 1, comprising the step of embedding the acetabular component, dual mobility bearing component, and femoral component such that a hemispherical outer bearing surface of the dual mobility bearing component articulates freely within the acetabular component and the head articulates freely within the inner bearing surface of the dual mobility bearing component.

24. 24. The method of claim 23, wherein the hemispherical bearing surface orients the bearing component within the acetabular component such that flexion-extension movement of the femoral component occurs primarily along the wider axis of the opening and adduction-abduction movement of the femoral component occurs primarily along the relatively narrower axis of the opening.

25. 24. The method of claim 23, wherein adduction and abduction of the femoral component is induced to occur primarily at the lateral bearing component by impaction of the neck of the femoral component against the high side of the rim along the relatively narrow axis of the opening.

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