Anatomical radial head artificial elbow joint

Abstract

Disclosed herein is an anatomically designed radial head prosthesis for improved anatomical fit and function and reduced likelihood of dislocation. The recessed, eccentric, and oriented, raised lateral bearing surface aspects of the radial head of the present invention improve tracking of the prosthetic radial head in the humeral capitellum and reduce its likelihood of dislocation.

Description

Technical Field

[0001] The present invention generally relates to an artificial elbow joint. More particularly, the present invention relates to an anatomical radial head artificial elbow joint.

Background Art

[0002] The elbow joint is a complex joint of the humerus, radius and ulna. The proximal head of the radius (the "radial head") articulates proximally with the capitulum of the humerus (radiohumeral joint) and medially with the radial notch of the ulna (radioulnar joint).

[0003] The radial head enables the radius to achieve different movements when the arm flexes and extends as the hand is pronated or supinated. During flexion and extension, the radial head articulates with the entire curved surface of the capitulum of the humerus, while the radioulnar joint functions as a hinge. When rotating the hand between the pronated and supinated positions, the radial head pivots on the capitulum of the humerus and the side surface of the radial head rotates within the radial notch.

[0004] Radial head artificial elbow joints are used to replace damaged radial heads and typically have a stem that is inserted into the radius and a head that articulates with the ulna and humerus.

[0005] The radial head conventionally had a substantially circular cross-section in the horizontal plane, but now the radial head includes an anatomically designed radial head that helps improve function and operation, including the Acumed Slide-Loc Anatomical Radial Head System <URL: https: / / www.acumed.net / system / files / Acumed-Surgical-Technique-EN-Slide-Loc-Anatomical-Radial-Head-ELB 10-03-F.pdf> United States Patent Application Publication No. 20170095338 (A1) filed on October 27, 2016, April 6, 2017, and International Publication No. 2005086939 (A2) pamphlet filed on September 22, 2005 (ACUMED LLC).

[0006] The present invention aims to provide an artificial elbow joint that improves anatomical compatibility, reduces the possibility of dislocation, and overcomes or significantly improves at least some of the drawbacks of the prior art, or at least provides an alternative.

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

Summary of the Invention

Problems to be Solved by the Invention

[0008] To improve anatomical compatibility and function and reduce the possibility of dislocation, an anatomically designed radial head artificial elbow joint is provided herein from cadaveric studies and digital CT scan reconstruction (digital segmentation) computer-aided modeling studies.

Means for Solving the Problems

[0009] It has been experimentally discovered that the aspects of the concave centroid eccentricity, orientation, and raised outer bearing surface of the radial head of the present invention improve the tracking of the artificial radial head of the capitulum humeri and reduce the possibility of its dislocation.

[0010] A further aspect of the artificial joint of the present invention can ergonomically accommodate the annular ligament of the elbow, improve surface contact with the radial notch in consideration of the anatomical shape of the radial notch, and conform to the anatomical shape of the radial head of the radius.

[0011] Furthermore, the radial heads of the present invention can be provided in different sizes according to the requirements of the patient, but there are specific geometric correlations between them that have been found to enhance anatomical compatibility between patients.

[0012] The artificial elbow joint of the present invention may further comprise a stem that may have an outer anatomical curvature, and this stem may be polished for press-fit (cementless) insertion that securely self-aligns within the proximal radial canal. The stem may be centered with respect to the radial head, which has been found to be in a better position for uniform distribution of joint articulation and rotational stresses. Further, the stem curvature may be directed away from the radial styloid process and toward the outside of the Lister's tubercle, preferably offset radially by about 30° with respect to the radial styloid process.

[0013] With the above in mind, according to one aspect, there is provided an artificial elbow joint comprising a radial head having an upper dish-shaped capitulum supporting surface and an inner radial notch supporting ulnar joint surface, the supporting surface defining a center of gravity of the supporting surface, and a recess is formed in the supporting surface to form a center of gravity of the recess, and the center of gravity of the recess is located forward with respect to the center of gravity of the supporting surface.

[0014] The ratio of the length between the center of gravity of the supporting surface and the center of gravity of the recess to the length between the center of gravity of the recess and the point on the rim of the supporting surface closest to the center of gravity of the recess may be greater than 25%.

[0015] This ratio may be about 33%.

[0016] The outside of the supporting surface may be raised.

[0017] The cross-section of the supporting surface may be non-circular.

[0018] The supporting surface may have an outer outermost point.

[0019] The outer outermost point may coincide with the axis of the maximum width of the supporting surface.

[0020] The axis of the maximum width may be an inner-outer direction axis.

[0021] The minimum / maximum diameter ratio of the supporting surface may be greater than 95%.

[0022] The cross-section of the supporting surface may be elliptical.

[0023] The recess can define the support axis vertically at the center of gravity of the support surface, the artificial elbow joint can define the rotation axis, and the support axis can be inclined with respect to the rotation axis.

[0024] The rotation axis and the support axis coincide above the radial head.

[0025] The support axis can be inclined 5 to 15° with respect to the rotation axis.

[0026] The rotation axis can be perpendicular to the horizontal plane.

[0027] The horizontal plane can be defined by the flat lower surface of the radial head.

[0028] The support plane defined by the rim of the support surface can be inclined with respect to the horizontal plane perpendicular to the rotation axis.

[0029] The rim can be on the same plane as the support plane.

[0030] The cross-section of the lower surface of the radial head can be circular.

[0031] The lower surface of the radial head can define a lower surface center of gravity that can be located in front of the center of gravity of the support surface.

[0032] The lower surface of the radial head can be flat.

[0033] The radial head can define a front cross-section raised profile that curves substantially uniformly from the lower surface of the radial head to the support surface.

[0034] The radial head can define a rear cross-section raised profile that can define an S-shaped flexed protrusion. Above the S-shaped flexed protrusion, the rear side transitions in a shape with a smaller curvature and a larger outward spread compared to the front side.

[0035] The ulnar articular surface can define a cross-section raised profile having a protrusion.

[0036] The protrusion can be located below one-third of the height between the lower surface and the support surface.

[0037] The ulnar articular surface is curved substantially uniformly above the overhang portion.

[0038] The ulnar articular surface is curved uniformly outwardly toward the bearing surface above the overhang portion.

[0039] The radial head may define a side cross-sectional profile having a lower portion, an overhang portion, and an upper portion.

[0040] The ulnar articular surface may define a cross-sectional raised profile having an overhang portion, and the overhang portion of the side cross-sectional profile may be located above the overhang portion of the medial ulnar articular surface.

[0041] The lower portion may be substantially perpendicular to a horizontal plane defined by the lower surface of the radial head.

[0042] The overhang portion is located substantially intermediate between the lower portion and the upper portion.

[0043] The radial extent of the lower portion may be substantially the same radius as the resected radius when installed in use.

[0044] The recess may be asymmetric in the anteroposterior direction in the horizontal cross-section.

[0045] The artificial elbow joint may further comprise radial heads of different sizes, and the minimum / maximum diameter ratio of its bearing surface may be substantially constant.

[0046] The artificial elbow joint may further comprise radial heads of different sizes, and the ratio of the diameter of its bearing surface to the displacement between the centroid of the recess and the centroid of the bearing surface may be substantially constant.

[0047] The artificial elbow joint may further comprise radial heads of different sizes, and the ratio of the diameter of the bearing surface to the height of the radial head may be substantially constant.

[0048] The artificial elbow joint may further comprise radial heads of different sizes, and the ratio of the diameter of its bearing surface to the diameter of the lower surface may be substantially constant.

[0049] The artificial elbow joint may further comprise radial heads of different sizes, and the ratio of the diameter of the bearing surface to the diameter of the recess may be substantially constant.

[0050] The artificial elbow joint may further comprise a stem having a posterolateral curvature.

[0051] The lateral curvature may comprise an upper portion and a lower portion, and an elbow forming a transition therebetween.

[0052] The cross-section of the upper portion may be non-circular.

[0053] The stem may define an axis offset with respect to the centroid of the bearing surface.

[0054] The radial head and the stem may be configured such that when the stem is inserted in use, the stem may be oriented away from the radial styloid process and towards the outside of the ulnar tuberosity of the elbow.

[0055] The stem may be oriented more than 20° away from the radial styloid process.

[0056] The stem may be oriented approximately 30° away from the radial styloid process.

[0057] Other aspects of the present invention are also disclosed.

[0058] Even if there are any other forms that may be included within the scope of the present invention, the preferred embodiments of the present disclosure will be described with reference to the accompanying drawings merely as examples.

Brief Description of the Drawings

[0059]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0060] The radial head 101 of the artificial elbow joint 100 replaces the excised radial head of the radius and has an inner ulnar joint surface 106 that joins with the radial notch of the ulna.

[0061] The medial and its derivatives shown in the figures indicate the side towards the ulna, and the lateral and its derivatives indicate the side away from the ulna. Further, posterior, anterior and their derivatives indicate the respective orthogonal axes in the horizontal plane.

[0062] The radial head 101 has an upper dish - shaped bearing surface 102 that articulates with the capitulum of the humerus.

[0063] A recess 104 is formed in the bearing surface 102. The bearing surface 102 defines a bearing surface centroid 103, which can be generally defined as the centroid of the uppermost rim 107 of the bearing surface 102 with reference to FIG. 4. Further, the recess 104 forms a recess centroid 105 that can be defined as the centroid of the recess contour 108 with reference to FIG. 4.

[0064] As shown in FIG. 4, the recess centroid 105 is located in front of the bearing surface centroid 103.

[0065] The center of gravity 105 of the bearing surface can be eccentrically located by more than one-fourth of the distance across the bearing surface 102 from the center of gravity 103 of the bearing surface. That is, the ratio of the length between the center of gravity 103 of the bearing surface and the center of gravity 105 of the recess, and the length between the center of gravity 105 of the recess and the closest point 109 of the rim, can be more than 25%.

[0066] In a preferred embodiment, the center of gravity 105 of the recess is located at approximately one-third of the distance across the bearing surface 102 from the center of gravity 103 of the bearing surface. That is, the ratio of the length between the center of gravity 103 of the bearing surface and the center of gravity 105 of the recess, and the length between the center of gravity of the recess and the closest point 109 of the rim, can be approximately 33%.

[0067] As most clearly shown in FIG. 2, the outside of the bearing surface 102 can be raised.

[0068] Referring to FIG. 4, the cross-section of the bearing surface 102 can be non-circular and can have an outer outermost point 110. As suggested above, the bearing surface 102 can be defined as being inside its uppermost edge 107. The minimum / maximum diameter ratio of the bearing surface 102 can be more than 95%. Further, the cross-section of the bearing surface 102 can be elliptical (i.e., symmetric with respect to only one axis, or oval).

[0069] As most clearly shown in FIG. 4, the bearing surface 102 is wider in the inner-outer direction compared to the front-back direction, and the outermost point 110 can coincide with the maximum width / inner-outer axis of the bearing surface 102.

[0070] As shown in FIG. 1, the recess 102 defines the support axis 111 vertically at the center of gravity 103 of the bearing surface. Further, the radial head 101 can define a rotation axis 112. The rotation axis 112 can be the axis about which the radial head rotates when articulating with the capitulum of the humerus. As shown in FIG. 2, the rotation axis 112 can be perpendicular to the horizontal plane 113 defined by the flat lower surface 114 of the radial head 101. The flat lower surface 114 can abut against the prepared flat surface of the resected radius.

[0071] As shown in FIG. 1, the support shaft 111 is inclined and displaced with respect to the rotation shaft 112, and the support shaft 111 and the rotation shaft 112 coincide above the radial head 104. The support shaft 111 can be inclined 5 to 15° with respect to the rotation shaft 112.

[0072] As shown in FIG. 2, the support surface rim 107 can define a support surface plane 115 inclined with respect to the horizontal plane 113. The support surface axis 111 can be perpendicular to the support surface plane 115.

[0073] As shown in FIG. 2, the rim 107 can be substantially in the same plane as the support surface plane 115.

[0074] Referring to FIG. 3, the cross-section of the lower surface 114 can be substantially circular. Further, the lower surface 114 can define a lower surface centroid 116. The lower surface centroid 116 can be located forward with respect to the support surface centroid 103.

[0075] As shown in FIG. 5, the radial head 101 can define a front surface 117 having a cross-sectional raised profile that curves substantially uniformly from the lower surface 114 to the support surface 102. The rear side 118 can define a cross-sectional raised profile that defines an S-shaped bent protrusion 119. Above the S-shaped bent protrusion 119, the rear side 118 transitions in a form with less curvature and a larger outward spread compared to the front surface 117.

[0076] FIG. 7 shows the cross-sectional raised profile of the medial ulnar articular surface 106 according to an embodiment, defining a protrusion 120, and above which the ulnar articular surface 106 curves substantially uniformly and outwardly toward the support surface 102.

[0077] The outer surface 121 can define a cross-sectional raised profile that defines a lower portion 122, a protrusion 123, and an upper portion 124. The lower portion 122 can be substantially orthogonal to the horizontal plane 113, and the protrusion 123 can be located substantially in the middle between the lower portion 122 and the upper portion 124. The radial range of the lower portion 122 is designed to have substantially the same radius as the resected radius below it, so as to ergonomically join with the annular ligament.

[0078] Referring to FIG. 4, the recess contour 108 can be asymmetric in the front-rear direction in a horizontal cross-section.

[0079] Radial heads 101 of different sizes can be provided, and the minimum / maximum diameter ratio of the bearing surface 102 remains substantially constant. That is, referring to FIG. 4, the ratio of the inner-outer direction width to the front-rear direction width of the bearing surface 102 can remain substantially constant.

[0080] Furthermore, the ratio of the diameter of the bearing surface 102 to the deviation between the recess centroid 105 and the bearing surface centroid 103 can remain substantially constant.

[0081] Furthermore, the ratio of the diameter of the bearing surface 102 to the diameter of the lower surface 104 can remain substantially constant.

[0082] Furthermore, the ratio of the diameter of the bearing surface 102 to the diameter of the recess 104 can remain substantially constant.

[0083] FIG. 8 shows a stem 125 that is integrally formed with the radial head 101 or can be attached to the radial head 101. The stem 125 can have a diameter smaller than the diameter of the lower surface 114 so as to abut against the prepared surface of the resected radius with the surrounding lower surface periphery exposed. The stem 125 can be polished and used for press-fit (cementedless) radius canal insertion.

[0084] As shown in FIGS. 8 and 9, the stem 125 can have an anatomical curvature in the posterolateral direction. The stem 125 can include a proximal portion 127, a distal portion 126, and an elbow 128 transition portion therebetween. The proximal portion 127 can have a length sufficient to transition to the proximal radius canal isthmus.

[0085] As shown in FIG. 9, the cross-section of the distal end 126 of the stem 125 can be circular, but the cross-section of the proximal end 127 can be non-circular such as elliptical.

[0086] Furthermore, the stem shaft 127 can be offset relative to the center of gravity of the bearing surface 103.

[0087] The foregoing description has used specific technical terms for illustrative purposes so that the present invention can be fully understood. However, it will be apparent to those skilled in the art that specific details are not required to practice the present invention. Accordingly, the foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and it is obvious that many modifications and variations are possible in light of the above teachings. The embodiments have been chosen and described in order to best explain the principles of the present invention and its practical applications, and thus enable others skilled in the art to utilize the present invention and various embodiments with various modifications suitable for the particular uses contemplated. The following claims and their equivalents are intended to define the scope of the present invention.

[0088] As used herein, the term "about" or similar terms should be construed to be within 10% of the stated value unless otherwise indicated.

Claims

1. An artificial elbow joint comprising a radial head having an upper dish-shaped capitulum humeri bearing surface and an inner radial notch bearing ulnar joint surface, wherein the bearing surface defines a bearing surface center of gravity, a recess is formed in the bearing surface to form a recess center of gravity, and the recess center of gravity is located forward of the bearing surface center of gravity.

2. The ratio of the length between the bearing surface center of gravity and the recess center of gravity to the length between the recess center of gravity and the point on the rim of the bearing surface closest to the recess center of gravity is greater than 25%. The artificial elbow joint according to Claim 1.

3. The outer side of the bearing surface is raised, and the cross section of the bearing surface is non-circular. The artificial elbow joint according to Claim 1.

4. The bearing surface has an outer outermost point that coincides with the inner and outer direction axis of the artificial elbow joint. The artificial elbow joint according to Claim 1.

5. The minimum / maximum diameter ratio of the bearing surface is greater than 95%. The artificial elbow joint according to Claim 1.

6. The cross section of the bearing surface is elliptical, and the cross section of the lower surface of the radial head is circular. The artificial elbow joint according to Claim 1.

7. The recess defines a support axis perpendicular to the bearing surface center of gravity, the artificial elbow joint defines a rotation axis, and the support axis is inclined with respect to the rotation axis. The artificial elbow joint according to Claim 1.

8. The lower surface of the radial head defines a lower surface center of gravity that is located forward of the bearing surface center of gravity. The artificial elbow joint according to Claim 7.

9. The radial head defines a front cross-sectional raised profile that curves substantially uniformly from the lower surface of the radial head to the bearing surface. The radial head defines a rear cross-sectional raised profile that defines an S-shaped bent and protruding portion. Above the S-shaped bent and protruding portion, on the rear side, the curvature is smaller compared to the front surface and transitions in a form with a larger outward spread. The artificial elbow joint according to claim 1.

10. The ulnar joint surface defines a cross-sectional raised profile having a protruding portion. The protruding portion is located below one-third of the height between the lower surface of the radial head and the bearing surface. The artificial elbow joint according to claim 1.

11. The radial head defines a side cross-sectional profile having a lower portion, a protruding portion, and an upper portion. The ulnar joint surface defines a cross-sectional raised profile having a protruding portion. The protruding portion of the side cross-sectional profile is located above the protruding portion of the ulnar joint surface. The lower portion is substantially perpendicular to the horizontal plane defined by the lower surface of the radial head. The protruding portion of the side cross-sectional profile is located substantially in the middle between the lower portion and the upper portion. The radial range of the lower portion is substantially the same radius as the resected radius bone when installed in use. The artificial elbow joint according to claim 1.

12. The horizontal cross-section of the concave portion is asymmetric in the front-rear direction. The artificial elbow joint according to claim 1.

13. Further comprising radial heads of different sizes, and the minimum / maximum diameter ratio of the bearing surface is substantially constant. The artificial elbow joint according to claim 1.

14. Further comprising radial heads of different sizes, and the ratio of the diameter of the bearing surface to the deviation between the center of gravity of the concave portion and the center of gravity of the bearing surface is substantially constant. The artificial elbow joint according to claim 1.

15. Further comprising radial heads of different sizes, and the ratio of the diameter of the bearing surface to the height of the radial head is substantially constant. The artificial elbow joint according to claim 1.

16. The artificial elbow joint according to claim 1, further comprising radial heads of different sizes, wherein the ratio of the diameter of the bearing surface to the diameter of the lower surface is substantially constant.

17. The artificial elbow joint according to claim 1, further comprising radial heads of different sizes, wherein the ratio of the diameter of the bearing surface to the diameter of the recess is substantially constant.

18. Further comprising a stem having a posterolateral curvature, The posterolateral curvature comprises an upper portion and a lower portion, and an elbow forming a transition therebetween. The artificial elbow joint according to claim 1.

19. The cross-section of the upper portion is non-circular, The stem defines an axis offset with respect to the center of gravity of the bearing surface. The artificial elbow joint according to claim 18.

20. The artificial elbow joint according to claim 18, wherein the radial head and the stem are configured such that when the stem is inserted during use, the stem is oriented away from the radial styloid process and towards the outside of the lesser tubercle of the elbow.

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