Joint prosthesis

[0002] This is a Divisional Continuing Application of prior application ser. No: 09/115,563 filed Jul. 15, 1998, now U.S. Pat. No. 6,099,571.

[0003] The invention relates to a joint prosthesis for joint replacement and especially a prosthesis for joint replacement of a finger or toe.

[0004] Surgically implantable prosthetic replacement devices are known in the art for replacement of joints in the hand or foot as well as elsewhere on the body. Often times these replacement devices are necessary as a result of accidents or diseases such as arthritis. It is desirable to provide a finger or toe prosthesis that imitates the natural range of movement of the replaced finger or toe, that allows slight twisting and lateral movement, but does not allow the joint to move in an unnatural way.

[0005] Another concern of a joint prosthesis is the potential failure of the device. Because of the small sized parts used in previous joint prosthesis, and especially when using metal, interfacing the prosthesis with the adjoining bones has been difficult. As a result, fatigue failures have occurred. It is therefore desirable to provide a joint prosthesis made of durable material compatible with human tissue and configured to minimize failure and to allow for replacement of the joint secondary to wear.

[0006] It is the intent of the current invention to address the aforementioned concerns. The prosthesis of the current invention duplicates the natural joint of a finger or a toe. The prosthesis includes a pair of intermedulary implants having a ball and socket combination therebetween. The two intermedulary implants/portions are inserted and anchored into the long shanks of the bone on either side of a faulty joint. Each intermedulary portion has a threaded end which is driven into the adjoining shanks of bone. A specialized driver is provided to screw the threaded ends into the shanks. The specialized driver has a head having a configuration corresponding to the exposed surface of each intermedulary portion to prevent slippage of the driver during insertion or removal of the implant. The bone and tissue surrounding the intermedulary implants may be allowed to heal within the patient with a temporary occupier filling the void of the faulty joint before insertion of the ball and socket configuration. The occupier may also provides a passive exerciser during the healing process to control movement of the surrounding muscles to prevent atrophy. Once the healing process is complete, the occupier is removed and the ball and socket configuration is then inserted to provide the necessary movement for the joint.

[0007] The socket has a generally hollow spherical configuration having a surface portion that corresponds and complements the exposed surface area of the intermedulary portions. The complementary surfaces provide a means for the surgeon or physician to incrementally adjust the socket relative to the intermedulary portion during the surgical installation of the ball and socket to provide correct relative positioning of the socket so that natural movement of the joint is realized. Once the socket is aligned to the intermedulary portion, a retaining screw secures the socket to the first intermedulary portion.

[0008] The socket has an open slot through the wall of the spherical body for access into the hollow interior by the ball member. The ball member is configured to enter the hollow interior through the slot in one direction and rotate within the hollow interior to confine the ball member therein. Once the ball member is captured within the hollow interior of the socket, another retaining screw secures the ball member to the second intermedulary implant. The ball member then has pivotal movement within the socket so that the second intermedulary implant pivots relative to the first intermedulary implant. The socket and ball member combination also includes a limiting means to limit the movement of the joint prosthesis to the natural movement of a finger or toe.

[0009] The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:

[0010] FIG. 1 is a side elevational view of a first embodiment of the joint prosthesis;

[0011] FIG. 2 is a top view of the joint prosthesis;

[0012] FIG. 2ais a side elevational view of an alternate intermedulary implant;

[0013] FIG. 3 is a sectional view taken along lines 3—3 of FIG. 1;

[0014] FIG. 4 is a perspective view of the joint prosthesis of the current invention in a finger;

[0015] FIG. 5ais a top plan view of a portion of a splined surface of the intermedulary implant;

[0016] FIG. 5bis a perspective view of a portion of the splined surface;

[0017] FIG. 6ais a side sectional view of a socket for the joint prosthesis of the present invention;

[0018] FIG. 6bis a sectional view taken along lines 6b—6bof FIG. 6a;

[0019] FIG. 6cis a sectional view taken along lines 6c—6cof FIG. 6b;

[0020] FIG. 6dis a sectional view taken along lines 6d—6dof FIG. 6a;

[0021] FIG. 7ais a side sectional view of a ball for the joint prosthesis of the present invention;

[0022] FIG. 7bis a sectional view taken along lines 7b—7bof FIG. 7a;

[0023] FIG. 7cis a sectional view taken along lines 7c—7cof FIG. 7a;

[0024] FIGS. 8a-8ftherein show the steps for inserting and positioning and securing the ball into the socket;

[0025] FIG. 9 is a partial side sectional view of the joint prosthesis in a straight position;

[0026] FIG. 10 is a sectional view taken along lines 10—10 of FIG. 9;

[0027] FIG. 11 is a sectional view taken along lines 11—11 of FIG. 9;

[0028] FIG. 12 is a partial side sectional view of the joint prosthesis having a 90° bend;

[0029] FIG. 13 is a sectional view taken along lines 13—13 of FIG. 12;

[0030] FIG. 14 is a side elevation view of the joint prosthesis when the joint has a bend greater than 90°;

[0031] FIG. 15 is a sectional view of the joint prosthesis in an extended position having an external hex end and a tapered opposing end;

[0032] FIG. 15ais a view of the hex end taken along lines 15a—15aof FIG. 15;

[0033] FIG. 16 is a sectional view of the joint prosthesis of FIG. 15 flexed in a 90° position;

[0034] FIG. 17 is a sectional view of the intermedulary implant having an external self holding tapered end;

[0035] FIG. 18 is a sectional view of a joint prosthesis implementing the intermedulary implants of FIG. 17;

[0036] FIG. 19 is a perspective view of a driving means having a splined end;

[0037] FIG. 20 is an elevational view of a retaining screw for a self holding taper;

[0038] FIG. 20ais a sectional view taken along lines 20a—20aof FIG. 20.

[0039] FIG. 21 is a partial sectional view of the socket and intermedulary implant connection having a self holding taper end;

[0040] FIG. 22 is a top view of an occupier attached to two intermedulary implants within a joint;

[0041] FIG. 23 is a sectional side view of the occupier attached to the two intermedulary implants; and

[0042] FIG. 24 is a side view of the occupier attached to the two intermedulary implants where the intermedulary implants are connected and articulated at 90 degrees; and

[0043] FIG. 25 is an exploded perspective view of the joint prosthesis described in FIGS. 1-3, with the intermedulary implant of FIG. 2A.

[0044] The prosthesis of the current invention duplicates the natural joint of a finger or toe. Looking first at FIGS. 1 through 4 and FIG. 25, the prosthesis 5 includes a pair of intermedulary implants 10 and 10a, a socket 12, a ball 14 within the socket 12, and a pair of retaining screws 16 and 16b. The intermedulary implant 10 indicates the proximal end of the joint, that is, the end closest to the wrist or ankle. The intermedulary implant 10aindicates the distal end of the joint, which is closest to the tip of the finger or toe.

[0045] In the first embodiment the intermedulary implant 10 in FIGS. 2 and 2ahas a threaded, pointed or tapered end 18 and an opposing end 20 or 20ahaving a threaded aperture 11 therein for later insertion of one of the retaining screws 16 or 16a. The opposing end surface 20 has a ratcheted or splined outer or facing surface having teeth 33 evenly spaced around the periphery of aperture 11. Partial end and perspective views of the splined surface 20 are shown in FIGS. 5aand 5b. The outer surface 13 of the intermedulary implant 10 may have threads 15 along its entire axial length or partially threaded with circumferential ratchets 17 extending another portion. In FIG. 1, an outwardly tapered surface 19 separates the threaded 15 portion from ratcheted portion 17 to expand the diameter of the intermedulary implant 10 adjacent to the splined surface 20 for receiving a retaining screw 16 therein. As will be described further, the ball or socket will have a complementary surface with the intermedulary implant.

[0046] An alternative intermedulary implant 10bis shown in FIG. 2ahaving a tapered and rounded end 18a. This implant is commercially available and manufactured by Steri-Oss, a Bausch & Lomb Company in California. The opposing end 20aof implant lob includes a flat horizontal surface having a hexagonal perimeter rather than the splined surface 20. A threaded aperture llais located through the hexagonal shaped end 20aand terminating approximately at half the axial length of the implant 10b. The configuration of the implant shown in FIG. 2amay replace either intermedulary implant 10 and 10ashown in FIG. 1. The ball or socket will have a complementary surface to abut the hexagonal flat surface of the intermedulary implant.

[0047] The geometry and dimensions of the intermedulary implants 10a, 10bwill depend upon the application as well as the patient's physical characteristics. The variables in the geometry of the intermedulary implant includes length, diameter, and thread pitch. A second or distal intermedulary implant is shown at element 10a. This corresponding intermedulary implant 10amay have the exact or different dimensions and configuration of intermedulary implant 10 or 10b. The distal intermedulary implant 10amay have the spline or hexagonal end or other configurations as disclosed hereinafter. Further, it is understood that any configuration disclosed for the proximal intermedulary implant 10 may be used for the distal intermedulary implant 10a. The intermedulary implant is preferably made of a Titanium metal material.

[0048] The joint prosthesis 5 also includes a ball 14 and socket 12 combination to connect the two intermedulary implants 10 and 10aand to provide the bending movement of the finger or toe. The socket 12 is shown in FIG. 6a-6dhaving an essentially spherical configuration having a hollow interior 23 and an extended portion 21 that faces the proximal intermedulary implant 10. The socket is preferably made of a Titanium material. The spherical body 26 has a through access port or slot 27 to the interior 23 of the socket for insertion of the ball 14 which will be discussed further. The extended portion 21 has an end mating surface 22 which corresponds to the end surface 20 of proximal intermedulary implant 10 or 10b. Therefore, in one instance, the end mating surface 22 of socket 12 would have a splined surface to matingly correspond with the splined surface 20 of intermedulary implant 10 as shown in FIGS. 1 and 2. In another instance, the end mating surface 22 may have a flat face, hexagonal shaped end to matingly correspond with hexagonal shaped end 20ain FIG. 2a. Other embodiments of corresponding surfaces will be discussed further. The splined surfaces 20 for connection between the intermedulary implant and socket provides the surgeon or physician incremental movement of the socket 12 relative to the intermedulary implant 10 without slippage when positioning the socket 12 onto the intermedulary implant 10 for correct relative positioning of the socket 12. The hexagonal shaped end 20aprovides six incremental positions to place the socket 12 onto intermedulary implant 10.

[0049] A through threaded aperture 25 extends from the end mating surface 22 in extended portion 21 to the hollow interior 23 of the socket 12. Once the correct positioning of the intermedulary implant 10 to the socket 12 is achieved, a retaining screw 16 is inserted into the through aperture 25 of the extended portion 21 of socket 14 so that the head 24 of retaining screw 16 is located in an expanded channel 35 and the shank of the screw 16aextends into threaded aperture 11 or 11aof the intermedulary implant 10 to hold and secure the proximal intermedulary implant 10 and socket 12 in a fixed and stationary manner relative to each other. The retaining screw 16 can be a tapered screw for metal or ceramic material or a large head screw for plastic material.

[0050] Once the first screw 16 is inserted to hold the socket 12 to the proximal intermedulary implant 10 the ball 14 is inserted into the through access port 27 of the socket 12. The ball is preferably made of a plastic material such as Delrin™. The ball 14 is shown in FIGS. 7a-7cand has the configuration of a spherical ball with two parallel sides sheared off. An arcuate tab 28 extends above the circular portion 29 of ball 14. A through aperture 30 is located between the center line C of ball 14 and the arcuate tab 28. Surrounding a first end 31 of aperture 30 is a circumferential splined surface 20d, a flat face hexagonal shaped end, or other configured surface disclosed herein to correspond to the splined surface, hexagonal shaped end, or other shaped surface disclosed herein of the intermedulary implant 11a. The other end 32 of aperture 30 has a greater diameter than the first end 31 of the aperture and a depth to receive the head 24 of another retaining screw 16aas discussed hereinafter.

[0051] The ball 14 is inserted into the hollow interior 23 of the socket 12 through access port 27 such that the sheared ends fit within the port 27 of the socket 12. The ball 14 is then turned to lock itself within the socket 12. FIGS. 8a-8fshows the series of maneuvers to insert the ball 14 into socket 12 and to secure it therein. The ball 14 enters socket 12 through access port 27 in an angular direction as designated by arrows R in FIG. 8aso that arcuate tab 28 fills the access port 27. When the ball 14 is positioned as shown in FIG. 8b, the ball is rotated counterclockwise as designated by arrow Q in FIG. 8c. FIG. 8dshows that the ball 14 is rotated 180° to reverse the directions of first end 31 and second end 32 of aperture 30 so that the ball 14 is shown as in FIG. 8e. The ball 14 is then rotated 90° as shown in FIG. 8fwhich essentially secures the ball within the interior 23 of socket 12.

[0052] Once the ball 14 is locked into the socket 12, the other retaining screw 16ais inserted through apertures 30 in the ball 14 so that the screw head 24ais positioned in end 32, and aperture 11bof the second intermedulary implant 10a, and tightens the ball 14 to the intermedulary portion 10a. The meeting surface 20dof end 31 of the ball 14 will have a complementary 20dsurface to surface 20 of intermedulary implant 10a. If the readily available hexagonal shaped ends are used, the surfaces may be adjusted in six increments of 60° before the ball 14 is secured to distal intermedulary implant 10a. If splined surfaces are used the degree of adjustability is greater. In either case, the ball 14 and second intermedulary implant 10aare secured together to allow limited movement within socket 12.

[0053] FIGS. 9-14 are views of the assembled joint prosthesis 5 in various positions to show other features of the invention. The arcuate extending tab 28 on the ball 14 is used as a guidance means for the ball 14 and allows pivotal movement of the ball 14 within the access port 27 of socket 12. The ball and socket configuration with the tab 28 allows very limited lateral motion or side to side motion of the joint for the finger or toe. Lateral motion is limited by the gap defined by the space between the stop portions 34 (the peripheral edges of access port 27) and the arcuate tab 28 (see FIGS. 2 and 10). FIGS. 9, 10 and 11 show the prosthesis when the finger (or toe) is in the extended or straight position. FIGS. 1 and 12 shows the ball 14 and socket 12 at a 90° bend. In FIGS. 1 and 12 there is also shown a pivotal stop 36 defined by the opposing edges of slot 27 to prevent overbending of the prosthesis to simulate the natural bending motion of the finger or toe. FIG. 14 shows the ball 14 and socket 12 at a bend greater than 90°.

[0054] The geometry of the intermedulary portion 10 may vary. The application and the size of the patient's digit will determine the length, diameter, the thread pitch, as well as other measurements of the intermedulary portion 10. Further, the application may vary the locations of pivot stop 36 on socket 12 and the gap between stops 34 and arcuate tab 28. The prosthesis 5 may also include a length extension 38 (FIG. 12) which may vary in length to join the intermedulary portion 10 or 10ato the ball 14 or socket 12. If a length extension 38 is required for the application, the complementary splined, hexagonal or other disclosed surface will be located on extension 38 to accurately position the corresponding surface of the ball.

[0055] Although the splined surfaces on the intermedulary implants 10, 10a, socket 12 and ball 14 provide a wider degree of adjustability for the surgeon than the flat surface hexagonal shape, the hexagonal shape provides manufacturing availability. FIGS. 15, 15aand 16 show the use of a hexagonal surface as discussed supra. Other surface configurations, i.e. octagonal, square etc., offering a certain degree of adjustability without slippage may be used.

[0056] FIGS. 17 and 18 show another surface configuration for the intermedulary implant 10 which allows an unlimited amount of rotating adjustability during the implant procedure. The connection end 40 distal from the tapered surface 18aof the intermedulary implant 10, 10ahas an outwardly tapered portion 42 that straightens to a vertical portion 44 at end 40. The socket 12 and ball 14 will each have a cavity 48 and 48acomplementary with respect to the configuration of the end 40. The outer surface end 40 is preferably smooth to provide unlimited rotating adjustability. The connection end 40 may also be configured to solely include an outwardly tapered portion 42 the entire length to base 46. FIGS. 20 and 20ashow modified retaining screw 116 and heads 124 for use with the self holding tapered ends 37.

[0057] FIG. 21 is a fourth embodiment for complementary surfaces between the intermedulary implant 10, 10band the socket 12. This mating surface configuration is not for use between the ball 14 and intermedulary implant 10abecause the surface is formed on the extended, portion 21 of the socket 12. FIG. 19 depicts a joint with an external self holding tapered end 37 on the socket 12 for receiving an internally tapered intermedulary portion as shown in FIG. 17. As can be seen, the intermedulary implant 10 can be connected to the extended portion 21 of the socket 12 in FIG. 18, to the ball 14 in FIG. 18, or to the self holding tapered end 21aof FIG. 19. If the socket 12 with the self holding tapered end 21ais used to connect to one of the intermedulary implant, the ball 14 and corresponding intermedulary implant may have any other complementary surfaces, such as the internal hex end on ball 14 with complementary flat face hex end 20aof intermedulary portion 10bas shown in FIG. 19. The spline surfaces and the internal self holding tapered surfaces are other alternatives. It is understood that the internal and external self holding tapered configurations offer the greatest amount of adjustability when implanting the prosthesis into the patient. The self holding tapered ends allow the physician to rotate the ball 14 and socket 360°. The external surface also inhibits slippage of the prosthesis 5.

[0058] The insertion of the prosthesis of the current invention is preferably performed as a two step procedure. Initially an operation will be conducted to remove the faulty joint. The surgery technique involves an incision on the dorsal surface of the digit over the joint area. The soft tissues are retracted. The desired length of the digit is estimated. The afflicted or diseased joint is resected. Using internally irrigated drill bits, which are commercially available, the intermedulary area of the bone, facing the cut end, is enlarged, shaped and thread tapped to match the intermedulary portion of the implant assembly. The intermedulary portion 10 or 10ais threaded into the bone. The appropriately sized occupier joint is selected and attached with screws 16 to the intermedulary portions 10, 10a. The tissues are repositioned and the wound is closed. A temporary occupier preferably made of a plastic material, such as Delrin™, will be inserted between the two intermedulary portions 10, 10ain place of the removed joint for a period of time while the intermedulary portions 10 and 10aand the adjoining tissue heal.

[0059] The illustrated occupier in FIGS. 22-24 is a two-piece structure having a first piece 47aattached to the proximal intermedulary portion 10 and a second piece 47battached to the distal intermedulary portion 10a. Each of the occupier pieces 47a, 47bhave a flat surface portion 61a, 61brespectively for abutment to respective ends 20, 20aof the corresponding intermedulary portion 10, 10a. Each occupier piece 47a, 47balso has a through aperture 63a, 63b, respectively, as can best be seen in FIG. 23, for receiving the retaining screw 16 to threadably secure the occupier piece 47a, 47bto the corresponding intermedulary portion 10, 10a.

[0060] Proximal occupier 47ais configured from the top view in FIG. 22 to have two rounded mound portions 65, 66 with a valley portion 67 therebetween. Distal occupier 47bis configured to complement the proximal occupier 47aso that from the top view (FIG. 22), the distal occupier 47bhas a rounded center section 69 which fits within valley portion 67. When the occupier and intermedulary portions are viewed from the side, FIG. 23 and FIG. 24, the distal occupier piece 47bhas a valley portion 70 for receiving one of the rounded mound portions 66 of the proximal occupier piece 47a. The valley portion 67 of the proximal occupier piece 47aand the valley portion 70 of the distal occupier piece 47bprovide only limited guidance for the corresponding rounded center section 69 and the rounded mound portion 66 when connected, as shown in FIG. 24, to maintain the two occupier pieces together and to allow only limited movement of the finger or toe. Once the intermedulary portions 10, 10aand occupier 47a, 47bare implanted, the incision is closed and the patient's hand or foot is put in a splint or cast. After primary healing, the splint may be removed and the joint may be passively exercised with a commercially available device to prevent atrophy. The passive exerciser gives direction within a fixed range to the movement of the joint. Alternating periods of rest for the joint while in a splint so that the surrounding soft tissue heals with periods of passive exercise is recommended until osseointegration is complete. Another operation will remove the occupier and insert the final ball 14 and socket 12 configuration as described supra.

[0061] As an aid to insert the intermedulary implants 10 and 10ainto the bone shanks, a driving means is provided to accommodate the various designs of the exposed ends 20, 20a, 40 the intermedulary implants. FIG. 19 shows a driving means 48 for exposed end 20 having a splined surface 50. A hex driver 48 has been devised in which a driver having a hex outer surface 54 has a serrated or splined surface 50 on one side to coincide with the serrated surface 20 of each intermedulary implant 10 and 10a. The hex driver 48 further includes an aperture 56 therethrough. A screw 58 is inserted into the aperture 56 of the hex driver 48 and screwed to drive the intermedulary implant 10 or 10ainto the bone shank. Once the intermedulary portion 10 or 10ais inserted, the screw 58 and the hex driver 48 are removed from the intermedulary portions 10, 10aso that the temporary occupier can be installed. If the exposed ends have a hexagonal configuration, a hex socket (not shown) can be used to drive the intermedulary implants 10, 10ainto the bone shank.

[0062] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.