Patent ID: 12213888

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In the following detailed description, reference is made to the accompanying drawings that depict by way of illustration specific embodiments for practicing the subject matter disclosed in this specification. These embodiments are described in sufficient detail to enable those skilled in the art to practice the subject matter of this specification. Other embodiments may be utilized and logical structural, mechanical, electrical, and chemical changes may be made without departing from the scope of this specification. To avoid detail not necessary to enable those skilled in the art to practice the embodiments described herein, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, with the scope of the illustrative embodiments being defined by the appended claims.

Referring toFIGS.1A-1B, one embodiment of elbow arthroplasty system10in accordance with the invention described herein includes a convex prosthetic component12, which is shown surgically attached to a proximal portion of an ulna14. Convex prosthetic component12is modular in nature and may be formed from medical-grade metallic, ceramic, and/or polymer-based materials. Convex prosthetic component12includes a ball16and a stem18that is surgically fitted to and affixed to the proximal ulna14preferably using bone cement, screws, pins, and/or press-fit fixation. Convex prosthetic component12may be cemented to ulna14or un-cemented with porous or bone ingrowth. Ball16is an ellipsoid with a major axis20. Ball16is joined to an end of stem18. Stem18includes a first section18athat extends into a cavity formed in the ulna14and a second section18bthat extends from first section18aaway from ulna14. Ball16and stem18are configured so that when first section18ais positioned within ulna14, ball16is positioned with respect to ulna14so that major axis20of ball16is generally aligned with a radial center of a trochlear notch22of ulna14. Stem18may include a positional guide or spacer that abuts ulna14when first section18ais inserted in ulna14to space ball16from ulna14the desired distance.

As shown inFIGS.2A-2B, elbow arthroplasty system10further includes a concave prosthetic component, or socket,24, which is shown surgically attached to a distal portion of a humerus26. Concave prosthetic component24is modular in nature and may be formed from medical-grade metallic, ceramic, and/or polymer-based materials. Concave prosthetic component24is surgically fitted to and affixed to the distal humerus26preferably using bone cement, screws, pins, and/or press-fit fixation. Concave prosthetic component24may be cemented to ulna14or un-cemented with porous or bone ingrowth. Concave prosthetic component24has a concave ellipsoidal surface28(FIG.3C) that defines a cavity30configured for receiving a portion of ball16. The trochlea of humerus is26is removed and a cavity is formed in humerus26for receiving concave prosthetic component24.

FIGS.3A-3Bshow an elbow32that includes elbow arthroplasty system10. Elbow arthroplasty system10replaces the humeroulnar joint of elbow32. Ball16is positioned within cavity30to mate convex prosthetic component12with concave prosthetic component24, as best shown inFIGS.3C-3D, which show elbow arthroplasty system10without ulna14and humerus26. The mating convex and concave prosthetic components12and24allow movement of ulna14relative to humerus26. During movement of ulna14relative to humerus26, convex prosthetic component12articulates with the matching concave prosthetic component24. Concave prosthetic component24is positioned with respect to humerus26so that major axis20of ball16is generally aligned with a center of rotation of a trochlea of humerus26. Ball16and concave prosthetic component24are positioned with respect to ulna14and humerus26so that as ball16articulates with concave prosthetic component24, ulna14moves with respect to humerus26in a manner that is similar to natural humeroulnar articulation.

Convex prosthetic component12may alternatively be attached to a proximal portion of radius34or to proximal portions of both ulna14and radius34. Further, convex and concave prosthetic components12and24may be spherical or spheroidal.

Referring toFIGS.4A-B, an alternative embodiment of elbow arthroplasty system is generally identified as100. Elbow arthroplasty system100is substantially similar to elbow arthroplasty system10except that it replaces both the humeroulnar joint and the humeroradial joint. Like elbow arthroplasty system10, elbow arthroplasty system100includes a convex prosthetic component102that mates with a concave prosthetic component, or socket,104. Convex prosthetic component102includes an ellipsoidal ball106and a stem (not shown) that is surgically attached to a proximal portion of an ulna108. Concave prosthetic component104has a concave ellipsoidal surface defining a cavity configured to receive ball106. Concave prosthetic component104is surgically attached to a distal portion of a humerus110. Ball106and concave prosthetic component104may be slightly larger than the ball16and concave prosthetic component24shown inFIGS.3A-3Bso that elbow arthroplasty system100is configured to replace both the humeroulnar joint (i.e., the joint between humerus110and ulna108) and the humeroradial joint (i.e., the joint between humerus110and radius112). Convex prosthetic component102may alternatively be attached to a proximal portion of radius112or to proximal portions of both ulna108and radius112. Convex and concave prosthetic components102and104may be spherical or spheroidal. Other than the differences described above, elbow arthroplasty system100is preferably configured substantially similar to elbow arthroplasty system10.

FIGS.5A-Bshow another alternative embodiment of elbow arthroplasty system generally identified as200. Elbow arthroplasty system200is similar to elbow arthroplasty system100in that it also replaces the humeroulnar and humeroradial joints. Elbow arthroplasty system200is further similar to elbow arthroplasty systems10and100except that the convex and concave prosthetic components202and204are reversed. Convex prosthetic component202is surgically attached to a distal portion of a humerus206, and concave prosthetic component, or socket,204is surgically attached to a proximal portion of an ulna208. Concave prosthetic component204may alternatively be attached to a proximal portion of radius210or to proximal portions of both ulna208and radius210. Convex and concave prosthetic components202and204may be spherical or spheroidal. Other than the differences described above, elbow arthroplasty system200is preferably configured substantially similar to elbow arthroplasty systems10and100.

Experimental Results

The ball-and-socket approach of elbow arthroplasty systems10,100, and200provides geometric constraints that mimic the natural constraint provided by articulation of the humerus trochlea and the ulna trochlear groove. Referring toFIGS.6-9, arthrokinematic motion of elbow arthroplasty system10with an ellipsoidal convex prosthetic component attached to the ulna and a matching concave ellipsoidal prosthetic component attached to the humerus is similar to that of a natural elbow.FIG.6shows abduction/adduction, internal/external, and flexion/extension rotation of the ulna relative to the humerus for a natural elbow and for the elbow arthroplasty system10. The data forFIG.6comes from optical motion measurements of a cadaver arm combined with computational simulations that included contact between articulating cartilage surfaces and ligaments. For the cadaver measurements, the humerus was fixed while the ulna was moved through its passive range of motion. A computational model was created specific to the measured cadaver arm and forces were applied in silico to the ulna such that experimentally measured ulna motion was reproduced. The dashed line inFIG.6labeled “Natural” shows these measurements. The natural humeral-ulnar joint was replaced by elbow arthroplasty system10and the same motion forces were applied to the ulna. The solid line inFIG.6labeled “EAS10” shows these measurements. Where the dashed line is not shown in the drawings, it is substantially overlapped by the solid line.FIG.7shows anterior/posterior, superior/inferior, and medial/lateral translation of the ulna relative to the humerus, for 25 seconds of simulation, for the natural elbow (dashed line) and elbow arthroplasty system10(solid line).FIGS.8-9show relative rotation and relative translation of the ulna relative to the humerus for the applied motion forces ofFIGS.6-7with an additional internal/external torque applied to the ulna. The applied torque was sinusoidal with a magnitude of 2000 N-mm. Measurements for the natural elbow are shown in dashed lines and for the elbow arthroplasty system10in solid lines. Elbow arthroplasty systems10and300(FIG.10) preferably have similar structures and geometries, and as such, elbow arthroplasty system300preferably functions in substantially the same manner as shown inFIGS.6-9to mimic the biomechanics and geometric constraints of a natural elbow. Elbow arthroplasty systems100,200,400(FIG.13),500(FIGS.16A-B), and600(FIGS.17A-B) may be configured to function in a different manner than as shown inFIGS.6-9.

Referring toFIG.10, an alternative embodiment of elbow arthroplasty system is generally identified as300. Elbow arthroplasty system300includes a convex prosthetic component302and a concave prosthetic component, or socket,304. Convex prosthetic component302includes a ball306that is a portion of an ellipsoid and is joined to an end of a stem308. Ball306is a truncated ellipsoid with an ellipsoidal outer surface306aand a flat surface306bthat is joined to stem308. Stem308includes a first section308aand a second section308b. First section308ais an elongate rod with a cross-section that is generally rectangular with rounded ends. Second section308bis shaped as a conical frustum tapering in size from first section308atoward ball306. First section308aof stem308may be surgically attached to a proximal portion of an ulna in a similar manner as shown inFIGS.1A-1Bfor stem18. Alternatively, stem308may be surgically attached to a proximal portion of a radius, proximal portions of a radius and an ulna, or a distal portion of a humerus. Second section308bmay abut a portion of an ulna, radius, or humerus when first section308ais inserted in a hole in the ulna, radius, or humerus to position ball306in a desired location with respect to the ulna, radius, or humerus. For example, second section308bmay abut the ulna, radius, or humerus to position ball306with respect to an ulna so that major axis314(FIGS.11A-B) of ball306is generally aligned with a radial center of a trochlear notch of the ulna. In this manner, second section308bacts as a spacer or positional guide that spaces ball306a desired distance from the ulna.

Concave prosthetic component304has a concave ellipsoidal surface310that defines a cavity312for receiving a portion of ball306. Concave prosthetic component304may be surgically attached to a distal portion of a humerus in a similar manner as shown inFIGS.2A-2Bfor concave prosthetic component24. Alternatively, concave prosthetic component304may be surgically attached to a proximal portion of an ulna, a proximal portion of a radius, or proximal portions of a radius and an ulna. Convex and concave prosthetic components302and304mate and articulate with each other in a similar manner as described above for elbow arthroplasty systems10,100, and200such that elbow arthroplasty system300mimics the natural articulation of an elbow when in use.

As shown inFIG.11A, there is an angle X between a major axis314of ellipsoidal ball306and first section308aof stem308. Angle X may be between 56 to 66 degrees, is more preferably between 59 to 63 degrees, and is most preferably approximately 61 degrees. The diameter d1of second section308bwhere it is joined to first section308amay be approximately 8 mm. The length L1of ball306along its major axis314may be approximately 18 mm. The width W1of first section308amay be approximately 4 mm, and the thickness T1of first section308amay be approximately 3 mm.

As shown inFIG.11B, the radius r1of ball306at a cross-section taken through its minor axis316may be approximately 6 mm. The length L2of second section308bfrom first section308ato ball306may be approximately 8 mm. The distance D1from second section308bto the major axis314may be approximately 4 mm. The combination of L2and D1, which is preferably approximately 12 mm, represents the distance from the bone to the major axis314of ball306when first section308aof stem308is inserted into the bone.

As shown inFIG.11C, there is an angle Y between first section308aof stem308and a central axis of the second section308bof stem308. Angle Y may be between 141 to 151 degrees, is more preferably between 144 to 148 degrees, and is most preferably approximately 146 degrees. The length L3of first section308amay be approximately 35 mm. The outer surface of second section308bmay taper at an angle of approximately 12 degrees from first section308ato ball306.

The angles X and Y and other dimensions referenced above preferably allow first section308ato be securely attached to an ulna, a radius, an ulna and a radius, or a humerus, and ball306to be positioned so that articulation of elbow arthroplasty system300is similar to a natural elbow.

Referring toFIGS.12A-D, concave prosthetic component304is generally a truncated ellipsoid with a hollow center that forms cavity312. A plurality of protrusions (one of which is identified as318) extend outward from an apex of an outer surface320. Further, two circumferential grooves322a-bextend around outer surface320. Grooves322a-bextend around outer surface320in planes oriented with a truncated surface323of concave prosthetic component304. Notches324a-dare further formed in outer surface320, as shown inFIG.12B. As shown inFIGS.12A-B, notches324a-dextend upward from truncated surface323approximately two-thirds of the way up toward the apex of outer surface320. Notches324aand324care oriented along a major axis of concave prosthetic component304, and notches324band324dare oriented along a minor axis of concave prosthetic component304. Protrusions318, grooves322a-b, and notches324a-dpreferably aid in surgically attaching concave prosthetic component304to an ulna, radius, or humerus. For example, protrusions318, grooves322a-b, and notches324a-dprovide rotational stability for concave prosthetic component304and allow bony ingrowth.

As shown inFIG.12C, an inner surface326of concave prosthetic component304includes concave ellipsoidal surface310and a cylindrical surface328. The distance D2from cylindrical surface328to the apex of inner surface326may be approximately 7 mm. The distance D3across a major axis330of ellipsoidal surface310may be approximately 21 mm. As shown inFIG.12D, a distance D4across a minor axis332of ellipsoidal surface310may be approximately 14 mm. The three principal semi-axes of ellipsoidal surface310are preferably 10.5 mm, 7 mm, and 7 mm, consistent with the distances D2, D3, and D4.

Elbow arthroplasty systems10,100,200,500, and600described herein may have similar dimensions as noted herein with respect to elbow arthroplasty system300.

Another alternative embodiment of elbow arthroplasty system is generally identified as400inFIG.13. Elbow arthroplasty system400includes a convex prosthetic component402and a concave prosthetic component, or socket,404. Convex prosthetic component402includes a ball406that is a portion of a sphere and is joined to an end of a stem408. Ball406is a truncated sphere with a spherical outer surface406aand a flat surface406bthat is joined to stem408. Stem408includes a first section408aand a second section408b. First section408ais an elongate rod with a cross-section that is generally rectangular with rounded ends. Second section408bis shaped as a conical frustum tapering in size from first section408atoward ball406. First section408aof stem408may be surgically attached to a proximal portion of an ulna in a similar manner as shown inFIGS.1A-1Bfor stem18. Alternatively, stem408may be surgically attached to a proximal portion of a radius, proximal portions of a radius and an ulna, or a distal portion of a humerus. Second section408bmay abut a portion of an ulna, radius, or humerus when first section408ais inserted in a hole in the ulna, radius, or humerus to position ball406in a desired location with respect to the ulna, radius, or humerus. For example, second section408bmay abut the ulna, radius, or humerus to position ball406with respect to an ulna so that central axis414(FIGS.14A-B) of ball406is generally aligned with a radial center of a trochlear notch of the ulna. In this manner, second section408bacts as a spacer or positional guide that spaces ball406a desired distance from the ulna.

Concave prosthetic component404has a concave spherical surface410that defines a cavity412(FIG.15C) for receiving a portion of ball406. Concave prosthetic component404may be surgically attached to a distal portion of a humerus in a similar manner as shown inFIGS.2A-2Bfor concave prosthetic component24. Alternatively, concave prosthetic component404may be surgically attached to a proximal portion of an ulna, a proximal portion of a radius, or proximal portions of a radius and an ulna. Convex and concave prosthetic components402and404mate and articulate with each other in a similar manner as described above for elbow arthroplasty systems10,100, and200such that elbow arthroplasty system400mimics the natural articulation of an elbow when in use.

As shown inFIG.14A, there is an angle X1between a central axis414of spherical ball406and first section408aof stem408. Angle X1may be between 56 to 66 degrees, is more preferably between 59 to 63 degrees, and is most preferably approximately 61 degrees. The diameter d2of second section408bwhere it is joined to first section408amay be approximately 8 mm. The diameter of ball406may be approximately 12 mm. The width and thickness of first section408amay be substantially the same as described above for first section308a.

As shown inFIG.14B, the length of second section408bfrom first section408ato ball406may be substantially the same as described above for second section308b(i.e., 8 mm). The distance D5from second section408bto the central axis414may be approximately 4 mm. The combination of the length of second section408and D5, which is preferably approximately 12 mm, represents the distance from the bone to the central axis414of ball406when first section408aof stem408is inserted into the bone.

As shown inFIG.14C, there is an angle Y1between first section408aof stem408and a central axis of the second section408bof stem408. Angle Y1may be between 141 to 151 degrees, is more preferably between 144 to 148 degrees, and is most preferably approximately 146 degrees. The length of first section408amay be substantially the same as described above for first section308a. The outer surface of second section408bmay taper at an angle that is substantially the same as described above for second section308b.

The angles X1and Y1and other dimensions referenced above preferably allow first section408ato be securely attached to an ulna, a radius, an ulna and a radius, or a humerus, and ball406to be positioned so that articulation of elbow arthroplasty system400is similar to a natural elbow.

Referring toFIGS.15A-C, concave prosthetic component404is generally a truncated sphere with a hollow center that forms cavity412. A plurality of protrusions (one of which is identified as418) extend outward from an apex of an outer surface420. Further, two circumferential grooves422a-bextend around outer surface420. Grooves422a-bextend around outer surface420in planes oriented with a truncated surface423of concave prosthetic component404. Notches424a-dare further formed in outer surface420, as shown inFIG.15B. As shown inFIGS.15A-B, notches424a-dextend upward from truncated surface423approximately two-thirds of the way up toward the apex of outer surface420. Notches424a-dare spaced apart from each other approximately 90 degrees around the circumference of outer surface420. Protrusions418, grooves422a-b, and notches424a-dpreferably aid in surgically attaching concave prosthetic component404to an ulna, radius, or humerus. For example, protrusions418, grooves422a-b, and notches424a-dprovide rotational stability for concave prosthetic component404and allow bony ingrowth.

As shown inFIG.15C, an inner surface426of concave prosthetic component404includes concave spherical surface410and a cylindrical surface428. Spherical surface410has a central axis430. The radius of spherical surface410may be approximately 7 mm.

Elbow arthroplasty systems10,100,200,500, and600described herein may have similar dimensions as noted herein with respect to elbow arthroplasty system400.

FIGS.16A-Bshow an elbow arthroplasty system500that includes a convex prosthetic component502and a concave prosthetic component504. Convex prosthetic component502includes a ball506that is joined to a base508. Ball506may be ellipsoidal, spheroidal, or spherical as described and shown above with respect to elbow arthroplasty systems10,100,200,300, and400. Base508includes two protrusions510,512that extend outward from base508. Protrusions510,512are shown inserted into holes formed in ulna514. Base508is surgically fitted to and affixed to the proximal ulna514preferably using bone cement, screws, pins, and/or press-fit fixation. Base508may be cemented to ulna514or un-cemented with porous or bone ingrowth. Ball506is preferably positioned with respect to ulna514as described above in connection with elbow arthroplasty system10.

Concave prosthetic component, or socket,504includes a concave surface516that may be ellipsoidal, spheroidal, or spherical as described and shown above with respect to elbow arthroplasty systems10,100,200,300, and400. Concave surface516is configured to receive ball506so that ball506articulates with concave surface516in a manner that is similar to natural humeroulnar articulation as described above with respect to elbow arthroplasty system10. Concave prosthetic component504includes a base518having two protrusions520,522that extend outward from base518. Protrusions520,522are shown inserted into holes formed in humerus524. Base518is surgically fitted to and affixed to the distal humerus524preferably using bone cement, screws, pins, and/or press-fit fixation. Base518may be cemented to humerus524or un-cemented with porous or bone ingrowth. Concave surface516is preferably positioned with respect to humerus524as described above in connection with elbow arthroplasty system10. Elbow arthroplasty system500may be configured to replace the humeroulnar joint, the humeroradial joint, or both the humeroulnar and humeroradial joints.

FIGS.17A-Bshow an elbow arthroplasty system600that includes a concave prosthetic component602and a convex prosthetic component604. Elbow arthroplasty system600is substantially similar to elbow arthroplasty system500except that concave prosthetic component602is joined to a proximal portion of an ulna606and convex prosthetic component604is joined to a distal portion of a humerus608.

Elbow arthroplasty systems10,100,200,300,400,500, and600are used in a similar manner. Accordingly, only use of elbow arthroplasty system10is described in detail herein. Convex prosthetic component12is joined to ulna14by forming a cavity in ulna14for receiving first section18aof stem18(FIGS.1A-B). First section18ais inserted into the cavity and ball16is positioned with respect to ulna14so that major axis20of ball16is generally aligned with a radial center of a trochlear notch22of ulna14. A positional guide or spacer on stem18(e.g. second sections308bor408b) may space ball16the desired distance. Convex prosthetic component12is surgically attached to ulna14using at least one of the following: bone cement, a screw or screws, a pin or pins, and press-fit fixation. Convex prosthetic component12may be cemented to ulna14or un-cemented with porous or bone ingrowth. Alternatively, convex prosthetic component12may be surgically attached to a humerus (e.g., similar to elbow arthroplasty system200), a radius, or a radius and an ulna.

Humerus26is prepared for receiving concave prosthetic component24by, for example, cutting or grinding away a portion of humerus26(FIGS.2A-B). Concave prosthetic component24is positioned with respect to humerus26so that major axis20of ball16(when ball16is received by concave prosthetic component24) is generally aligned with a center of rotation of a trochlea of humerus26. Concave prosthetic component24is surgically attached to humerus26using at least one of the following: bone cement, a screw or screws, a pin or pins, and press-fit fixation. Concave prosthetic component24may be cemented to ulna14or un-cemented with porous or bone ingrowth. Alternatively, concave prosthetic component24may be surgically attached to an ulna (e.g., similar to elbow arthroplasty system200), a radius, or a radius and an ulna.

Ball16is aligned with concave prosthetic component24in the manner shown inFIGS.3A-3Dand positioned within cavity30. Ball16is then able to articulate with respect to concave prosthetic component24in a manner that is similar to natural humeroulnar articulation.

While this specification describes a number of embodiments, aspects of each embodiment may be applied to other embodiments. Thus, this specification contemplates that the various features of the embodiments may be combined with one another.