ANTERIOR CRUCIATE LIGAMENT PROSTHESIS

Abstract: An adjustable housing (20) suitable to be used with another housing (18) and with a synthetic ligament (22) so as to provide (for example) an anterior cruciate ligament prosthesis system (16) for a knee joint is provided. The adjustable housing (20) features an interior having a step shoulder (46) located therein. A set screw (32) in the housing (20) fixes the synthetic ligament (22) at a desired level of tension. The system (16) has many significant advantages including (but not limited to) being able to withstand very high loads and being able to be retensioned repeatedly and easily without replacing the artificial ligament (22).

Description: In the field of orthopedics, rupture of anterior cruciate ligaments has been a problem which has been addressed by various solutions. See, for example, U.S. Patent No. 4,605,414 to Czajka, "Reconstruction of a Cruciate Ligament"; U.S. Patent 4,400,833, to Kurland, "Means and Method of Implanting Bioprosthetics"; and U.S. Patent 3,797,047 to Pillet, "Artificial Tendon." FR-A-2586927 and DE-A-2400834 describe ligament prostheses for a joint in which an artificial ligament is attached to fixing members located on respective bones forming the joint. However, despite this and other work, a need has continued to exist for a system which can withstand higher loads than have previously been possible, which permits an unlimited number of retensionings to be made, and in which it is not difficult to replace a synthetic tendon. To date, such a system has not previously been known. It is an object of this invention to provide a system for replacement of a natural anterior cruciate ligament having excellent strength properties, excellent short and long term stability, and ability to undergo a very large number of retensionings without replacement of the artificial ligament; however, if replacement of that ligament is required, it can easily be accomplished. A further object of this invention is a fixator or housing suitable for use in an anterior cruciate ligament prosthesis system which has great strength, retensioning capabilities, short and long stability, and in which parts can be rapidly and simply replaced. A further object of this invention is an improved system for an anterior cruciate ligament prosthesis in which either one or multiple cords can, if desired, be used. These and other objects are satisfied by the anterior cruciate ligament prosthesis of the invention which comprises an adjustable housing to be relatively permanently implanted into a bone bore in either the tibia portion (or the femoral portion) of a knee joint and to work as a fixator for a ligament extending therethrough, the adjustable housing having the following features, including a step shoulder located therein which connects a first bore and a second bore which are not coaxial but which are both located substantially longitudinally within the adjustable housing, the adjustable housing having also a third bore which intersects the step shoulder at an angle of about 90° and which is adapted to house a set screw to about the ligament passing through said first and second bases. Preferably, the adjustable housing will be relatively permanently implanted into the tibia portion of a knee joint and will be used within a second housing which is relatively permanently implanted into the femur portion of the knee joint. The second housing can be but need not be an adjustable housing as described above. The step shoulder preferably intersects both the first bore and the second bore at an angle of about 45°, although any angle greater than 0° and less than about 90° is within the scope of this invention. The adjustable housing may be in the form of a step drill made up of a larger diameter substantially cylindrical portion which is joined to a smaller diameter substantially cylindrical portion. In a preferred embodiment, the adjustable housing is placed into a bore in the tibial side of the knee joint. Fig. 1 is a pictorial representation of a normally occurring, healthy anterior cruciate ligament. Fig. 2 is a pictorial representation of a system of a preferred embodiment of a prosthetic replacement for the normal anterior cruciate ligament, according to the invention. Fig. 3 is a plan view of a preferred embodiment of a prosthesis system according to the invention, including various parts of that preferred embodiment useful for replacing the normal anterior cruciate ligament. Fig. 4 is a cross-sectional view, taken along the line 4-4 in figure 3, of a preferred embodiment of a housing according to the invention for placement preferably into a femoral portion of a knee joint, showing a shoulder step, set screw, slot, and porous coating. Fig. 5 is a view in cross section taken along the line 5-5 of figure 3, showing a preferred embodiment of the housing of the invention suitable for placement preferably into a tibial portion of a knee joint. Fig. 6 is an elevational view of either housing shown in figure 3. Fig. 7 is a plan view showing a set screw, together with a "tee" bar which is to be used in a preferred embodiment according to the invention. Fig. 8 is a cross-sectional view of a preferred embodiment of an anterior cruciate ligament prosthesis system according to the invention when it is implanted into a knee joint, showing the positioning and shape of a preferred embodiment according to the invention of an adjustable housing (on the lower right hand portion of figure 8) for use preferably in a tibia part of a knee joint, the exterior surface of that housing being flush with the surface of the tibia and showing an adjustable housing (in the upper, left-hand corner of figure 8) for use preferably in the femur part of a knee joint. Fig. 9 is a plan view showing a set screw with a ball fixed within the set screw which abuts against a portion of a metal sleeve. This is an alternative embodiment to the set screw with "tee" bar shown in figure 7. Fig. 10 is an elevational view of an embodiment of an adjustable housing according to the invention for use in an anterior cruciate ligament prosthesis system, showing a metal sleeve with a tab portion to be inserted into the housing so that the set screw will contact the metal sleeve when the set screw is inserted into the housing. Fig. 11 is a cross-sectional view, taken along the line 11-11 in figure 10. Fig. 12 is a cross sectional view, taken along the line 11-11 in figure 10, after the set screw has been inserted into the housing and contacts the metal sleeve. In Fig. 1, a pictorial representation of a normal anterior cruciate ligament 10 is shown, together with the tibial portion 12 of a knee joint and a femoral portion 14 of that knee joint. In Fig. 2, a preferred embodiment of an anterior cruciate ligament prosthesis 16 according to the invention is shown generally, located within a knee joint. In Fig. 3, an exploded view of an anterior cruciate ligament prosthesis system 16 according to the invention is shown, with component parts tibial housing 18, femoral housing 20, filament 22 (also referred to as an artificial ligament or artificial tendon), and spacers 24. Also shown in Fig. 3 are slots 26 and 28 and set screws 30 and 32 located in tibial portion 18 and femoral portion 20, respectively. Also shown in Fig. 3 is step drill 34 made up of larger diameter cylindrical portion 36 and smaller diameter cylindrical portion 38. Likewise, femoral portion 20 has a step drill 40 made up of larger diameter cylindrical portion 42 and smaller diameter cylindrical portion 44. Fig. 4 is a cross-sectional view, taken along the line 4-4 in Fig. 3. A step shoulder 46 connects a first bore 48 located in larger diameter cylindrical portion 42 with a second bore 50 located in smaller diameter cylindrical portion 44. It is noted that second bore 50 is a substantially longitudinal bore and is located in a substantially centered position within smaller diameter cylindrical portion 44, whereas first bore 48 is located substantially longitudinally within larger diameter cylindrical portion 42 but is not centered therein. Also shown in Fig. 4 is a third bore 52 located within femoral housing 20. Set screw 32 is adapted to be positioned within third bore 52 and is intersected on its interior end by "tee bar" 56 (also shown in Fig. 7). Also shown is a porous metal coating 58 located on the exterior of larger diameter cylindrical portion 42 of femoral housing 20. In Fig. 5, a cross-sectional view taken along the line 5-5 in Fig. 3 shows tibial housing 18 with larger diameter cylindrical portion 36 having a porous metal coating 58 and smaller diameter cylindrical portion 38. Also shown is step shoulder 60 connecting first bore 62 and second bore 64. Set screw 30 is located within third bore 66. Surface 68 is angled so that when tibial housing 18 is suitably inserted into a bore in the tibia, surface 68 will be flush with the exterior surface of the tibia. Surface 68 is shown in fig. 5 making an angle of 45° with the vertical. In Fig. 7, a set screw 30 (with a hexagonal indentation 69) is shown, with a "tee" bar shown for use therewith. In Fig. 8, is shown a preferred embodiment of the apparatus of the invention, as was shown and described in Figs. 3-7, implanted within a tibia portion 12 of a knee joint and a femur portion 14 of that knee joint. It is noted that surface 68 is flush with the surface of tibia 12, and surface 70 (also shown in fig. 4) is preferably slightly below the surface of femur 14. Surface 70 is shown in fig. 4 at an angle of 15° with the vertical. Filament 22 is shown in a taut position. In Fig. 9, is shown a set screw 30 having an integrally attached metal ball 56 which abuts against metal sleeve 72. The nose 51 of the housings sections 38, 44 has an internal radius 53 designed to protect ligament material from fraying relative to range of motion. In Fig. 10, metal sleeve 72 is shown in greater detail, with a tab portion 74 (which fits into key 26 in tibial housing 18). In Fig. 11, which is a cross-sectional view taken along the line 11-11 in Fig. 10, set screw 30 is shown positioned within third bore 66 in a tibial housing 18, together with metal sleeve 72 located within first bore 62 in tibial portion 18. Set screw 30 is shown not yet contacting metal sleeve 72, and no "tee" bar is shown in this figure. In Fig. 12, also taken along the line 11-11 in Fig. 10, set screw 30 is shown in its fully implanted position, contacting metal sleeve 72. In the practice of the invention, it is required that at least one of the two housings used in the anterior cruciate ligament prosthesis system of the invention be adjustable, and it is preferred that the housing portion which is implanted into the tibia be the adjustable portion. An adjustable housing according to the invention can be used, if desired, with another adjustable housing according to the invention; or an adjustable housing of the invention can be used with any other suitable means for fixing one end of an artificial ligament. An adjustable housing according to the invention can be used to house a single filament (or artificial ligament or tendon), or alternatively, if desired, can be used with two or more ligaments, each filament preferably having its own first, second, and third bores located within the adjustable housing. A step shoulder located within the adjustable housing connects to longitudinal bores located within the housing, and preferably it connects those two bores such that the step shoulder intersects each bore at an angle greater than 0° and less than about 90°, preferably at about 45°, and most preferably at 45°. A third bore located within the housing is adapted to house a set screw so that the ligament can be passed through the first bore and second bore of the adjustable housing and contacted by the set screw (and thereby held in place). Preferably, the adjustable housing is in the form of a step drill, having a larger diameter cylindrical portion and a smaller diameter cylindrical portion. This feature provides initial stability to the prosthesis when it is implanted into a bone bore. When a porous metal coating 58 is located on the housing, preferably on the outer surface of the larger diameter cylindrical portion, bone can grow into the housing and provide long term stability. However, because of the cylindrical shape, if necessary the housing can be cut from the bone interface with a core drill and relatively easily removed. Preferably, a slot is located on the outer surface of the housing and is useful for aligning the prosthesis within the bone bore. Preferably a metal sleeve (made of thin metal and crimped) is placed onto the ligament, such that the set screw will rotate on a piece of static metal (provided by the metal sleeve) when the ligament is fixed by the set screw. The sleeve is preferably split so that the set screw collapses the sleeve. Only the tab drives into the ligament, not the set screw. This preferred sleeve prevents fraying of the ligament by the set screw. The set screw(s) can be any suitable set screw(s), for example hexagonally indented set screw(s). Importantly, the set screw should meet the step shoulder within the housing at an angle which is about 90°. This angle prevents fraying of the artificial ligament. If an adjustable housing is to be used for multiple cords, a set screw will be placed across each shoulder located within the housing such that each set screw contacts a ligament located within a shoulder at an angle of about 90°. Spacers (which are conveniently available in 1 mm or 2 mm sizes) can be used with the prosthesis of the invention if necessary, for example, if the surgeon has over-drilled the bone bore in the tibia or in the femur. Within the housing, the set screw (or screws, if multiple filaments are being used) clamps down on the filament, locking it in place. The "tee" bar which is free to swivel within the set screw provides a surface which does not fray the cord or ligament. The step shoulder located within the housing provides additional support against slippage of the filament within the housing. It is preferred that the length of the step shoulder be such that both the first bore and the second bore within the housing intersect that step shoulder at an angle of about 45°. Preferably a solid core filament is used in the prosthesis of the invention. However, other types of filaments can also be used, if desired. For example, a hollow core filament could be used, especially if a solid core portion were inserted into each end of the hollow core, to be contacted by preferably a metal sleeve which is contacted by a set screw within an adjustable housing. The anterior cruciate ligament prosthesis system according to the invention exhibits the following advantages and characteristics. The fixators or housings generally will not be changed. This is quite different from what has been known in the prior art. In the prosthesis of this invention, the ligament tension can be adjusted or the ligament can be exchanged very rapidly and simply. Multiple tension adjustments can, also, be made before implanting surgery has been completed. A very stable device capable of withstanding very large loads is provided by the device of the invention. It is believed that the prosthesis of the invention is capable of withstanding significantly higher loads than other anterior cruciate ligament prostheses which have previously been known. The adjustable housing of the invention (as shown in Figs. 3, 4 and 5), is preferably made by the following procedure. A housing having a larger and a smaller diameter cylindrical portion can be made by any suitable procedure. Also, any suitable procedure for producing a first, second and third bore (as described above) within the housing can be used. A channel is cut for the porous metal coating 58. Porous metal coating 58 is preferably a 2-layer metal coating, deposited preferably by the procedure as described in U.S. Patent 4,550,448 to Kenna. Filament or synthetic ligament 22, which preferably is a solid core filament, can be made by any suitable procedure. The anterior cruciate ligament prosthesis of the invention can be positioned in the knee joint preferably in the following manner. First a relatively small diameter bore is drilled through the tibial and femoral portions of the knee joint bones in any suitable manner. The bore must be large enough to house the synthetic ligament. Next, a larger diameter bore is made to a depth in the bone equal to the length of the housing to be implanted into the tibial or femoral portion of the knee joint. The diameters of the bores should be chosen so as to contain the housings to be implanted. Then a housing is positioned and relatively permanently fixed on the femoral side of the bone bore with a first end of a filament 22 extending from the housing and extending through the bone bore. The second end of the filament is fixed by (or within) the ligament housing. The first end of the filament 22, which exits from the bone bore is then passed into the second bore 64 (located within the smaller diameter cylindrical portion) of the tibial housing 18, past the step shoulder 60, and then into and through the first bore 62 in the larger diameter cylindrical portion of tibial housing 18, such that the free end of filament 22 extends from the housing 18. The filament 22 is then pretensioned with, for example, a spring-loaded device; and the tension is either increased or decreased. The ligament is then fixed in place by turning down set screw 30 so that "tee" bar 56 contacts the ligament 22 or preferably the metal sleeve 72. If two adjustable housings are used in the system, and if it is desired to replace the ligament 22, the surgeon can merely back off set screws 30 and 32 and thread through the two housings a new ligament 22. The set screws 30 and 32 can then be repositioned, once the desired tension has been achieved. It is believed that the adjustable housing of the invention can be used for other uses, wherever there is a need for an adjustable housing having the advantages as described above.

Claims: 1. A housing 20 for a ligament prosthesis adapted to be implanted in a bone bore and to work as a fixator for a ligament extending therethrough, characterised in that the housing 20 contains a step shoulder 46 which connects a first bore 48 and a second bore 50, said bores being located substantially longitudinally but not coaxially within the housing, and the housing also comprises a third bore 52 having a centerline which intersects said step shoulder 46 at an angle of about 90°, said third bore being adapted to house a set screw 32 to abut the ligament passing through said first and second bores. 2. A housing according to claim 1 in which said step shoulder 46 connects with said first bore 48 at an angle of about 45° and wherein said step shoulder 46 connects with said second bore 50 at an angle of about 45°. 3. A housing according to claim 1 or 2 comprising a step drill made up of a larger diameter substantially cylindrical portion 36 joined to a smaller diameter substantially cylindrical portion 38 and wherein said larger diameter substantially cylindrical portion 36 houses said first bore 48 and said smaller diameter subtantially cylindrical portion 38 houses at least a portion of said second bore 50. 4. A housing according to claim 3 having a slot 28 located at the outer extremity of said larger diameter cylindrical portion 36 and wherein said slot 28 is suitable for aiding in positioning the housing. 5. A housing according to claim 3 or 4 having a porous metal coating 58 located on the outer cylindrical surface of said larger diameter substantially cylindrical portion 36. 6. A housing according to claim 5 having a metal sleeve 72 which is substantially cylindrical in shape and-which has a diameter slightly smaller than the diameter of said first bore 48 wherein said metal sleeve 72 is adapted to contain a filament 22 and then be inserted into said first portion so as to provide a metal surface to be contacted by a set screw 32. 7. A housing according to claim 6 in which said metal sleeve 72 comprises at least one tab portion 74 located therein which is to be used for aligning said metal sleeve 72. 8. A housing according to claim 7 which includes also a spacer 24 in the shape of an annulus having an internal diameter substantially equal to the outer diameter of said smaller diameter cylindrical portion 38 of said first housing 20. 9. A housing according to any preceding claim including a set screw 32 secured within said third bore 52. 10. An anterior cruciform ligament prosthesis comprising a housing 20 as claimed in claim 9 and a solid core filament 22 positioned in said first and second bores and fixed therein by means of said set screw 32. 11. A ligament prosthesis according to claim 10, comprising a second housing 18 substantially similar to said housing 20, said housings to be implanted in bone bores in the tibia and femur portions respectively of a knee joint.

Inventors: KENNA, ROBERT VINCENT
Applicants: PFIZER HOSPITAL PRODUCTS GROUP, INC.
Application year: 1989
Main classification: A61F2
IPC codes: A61F2