Patellar ligament spacer for ACL injuries

Abstract

A method and implant to treat anterior cruciate ligament (ACL) injuries are disclosed. The method involves advancing the insertion of the patellar ligament to the proximal tibia. The implant includes a spacer (30) which is inserted between the patellar ligament and the tibia and fixed to the tibia. The spacer decreases the angle between the patellar ligament and the tibia plateau and consequently modifies the internal joint force, restoring stability to the joint even if the ACL is ruptured. The method and implants are applicable to both human and canine patients.

Claims

1. A spacer for implantation onto an anterior aspect of a tibia of a knee, and under a patellar ligament proximally to a location where an end of the patellar ligament is attached to the tibia, the spacer comprising: a first surface adapted to face the patellar ligament; a second surface adapted to face the tibia, wherein the first and second surfaces are directly connected to one another at respective peripheral edges thereof; and at least one screw anchor fixation for the tibia, wherein the first surface has a concave surface portion and a convex surface portion, wherein the concave surface portion and the convex surface portion intersect each other, such that a groove is formed on a medial portion of the first surface between two ridges; wherein the ridges have extending therefrom a respective side flange, each side flange forming opposed, lateral side faces extending between the first and second surfaces, such that one edge of each side face coincides with an edge of the intersecting concave and convex surface portions of the first surface and a different edge of each side face coincides with an edge of the second surface, at least one side flange including a conical blind hole; wherein each of the at least one screw anchor fixation comprises a conical head configured to protrude above a surface of the tibia when the screw anchor fixation is screwed into the tibia, and wherein the conical blind hole is configured to receive the conical head and wherein an angle of the conical head and the conical blind hole is self-locking, and whereby the spacer is configured to extend anteriorly such that the patellar ligament is held away from the tibia to alter an angle between the patellar ligament and an axis tangent to a tibial plateau of the tibia.

2. The spacer of claim 1, wherein the first surface has a polished finish and the second surface is adapted for bony integration.

3. The spacer of claim 1, wherein the first surface and the second surface are both adapted for bony integration.

4. The spacer of claim 1, wherein the angle between the patellar ligament and the axis tangent to the tibial plateau of the tibia is 90 degrees when the knee is extended.

5. The spacer of claim 1, wherein the spacer is dimensioned so as to decrease the angle between the patellar ligament and the axis tangent to the tibial plateau of the tibia by 5 to 15 degrees in dogs.

6. The spacer of claim 1, wherein the spacer is dimensioned so as to decrease the angle between the patellar ligament and the axis tangent to the tibial plateau of the tibia by 10 to 30 degrees in humans.

7. The spacer of claim 1, comprising at least two screw anchor fixations for the tibia.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side view of a dog knee joint (stifle) on which the TTA procedure has been performed.

(2) FIG. 2 is a side view of a dog knee joint having a patellar ligament spacer according to an embodiment of the invention.

(3) FIG. 2a is a cross sectional view of the dog knee joint of FIG. 2 through the spacer.

(4) FIGS. 3a-3d illustrate mechanisms for fixing a spacer in a dog knee.

(5) FIG. 4 is a side view of a human knee with a patellar ligament spacer according to an embodiment of the invention.

(6) FIGS. 5a-5c are front, side and top views of a spacer for a human knee joint according to an embodiment of the invention.

DETAILED DESCRIPTION

(7) The present invention provides a spacer and a procedure for adjusting the position and angle of the patellar ligament in order to stabilize the knee. The knee is stabilized through geometric changes similar to those achieved by TTA in a much less invasive procedure. The TTA procedure is explained in connection with FIG. 1 to illustrate stabilization of the knee. The TTA procedure is currently accepted as a standard treatment for ruptured ACL in dogs (Fossum T W, Small Animal Surgery, Elsevier Health Sciences, 3.sup.rd edition, 2007; Boudrieau R, Tibial Plateau Leveling Osteotomy Or Tibial Tuberosity Advancement?, Vet. Surg. 38:1-22, 2009). FIG. 1 illustrates the knee joint both before and after the TTA procedure. The tibia 1 and the femur 2 articulate at the knee joint via condyles of the femur 21 and condyles of the tibia, also commonly referred to as the tibial plateau 20. Pull 24 from the quadriceps muscles acts on the patella 3, which in turn pulls onto the tibia via patellar ligament 5 (4 in its original orientation). The force between the condyles of the femur and the tibia is approximately parallel to the patellar ligament 5, having been tilted from its original orientation 6 before the advancement (which was parallel to 4) into the new orientation 7, which is perpendicular to the plateau 20. When the joint force 7 is perpendicular to the plateau 20, neither the cranial (anterior) 8, nor the caudal (posterior) cruciate ligament 9 are needed to stabilize the joint. When this condition is satisfied in the extended position of the knee, such as shown on FIG. 1, the joint will also be stable when flexed, stability provided by the caudal (posterior) cruciate ligament.

(8) Advancement of the tuberosity, after an opening wedge osteotomy, is maintained by a cage 13 fixed to the tibia with a posterior screw 14 and an anterior screw 15. The tension of the patellar ligament 5 is transferred to the body of the tibia via a tension-band plate 10, fixed distally to the tibia with screws 11, and proximally to the tuberosity with a fork 12.

(9) In addition to balancing the internal force 7 of the knee joint, TTA also reduces the force 23 (originally 22) between the patella and the femur. A procedure similar to TTA has been invented and performed in human surgery as well by Maquet (Maquet P; Advancement Of The Tibial Tuberosity, Clin. Orthop. Rel. Res. 115: 225-230, 1976).

(10) The procedure of the present invention provides similar changes to those of TTA without the need to cut and reattach the tuberosity. The advantages of the invention are obtained through placement of a spacer between the tibia and the patellar ligament. FIG. 2 shows a medio-lateral view of a dog knee in the extended position with a spacer 30 of the present invention. Patellar ligament has been rotated from its original position 34 to a new position 35 by insertion of a spacer 30 between the patellar ligament and the tibia just proximally to the insertion point 36 of the ligament 35 (34) to the tibia 1. The angle 31 between the patellar ligament 35 and the tibial plateau 20 should be about 90 degrees when the knee is extended to keep the knee stable. In dogs, this calls for an average rotation of the patellar ligament on the order of 5 to 15 degrees; in humans, a larger correction of 10 to 30 degrees is needed for a full compensation of a ruptured ACL. FIG. 2a shows a cross-section through the spacer 30 and the tibia 1. The spacer should preferably be slightly grooved under the ligament so as to keep it in a stable position. This, however, is not an essential requirementproximity of the insertion should guarantee a stable guidance of the ligament over the spacer.

(11) Under the same pull of the quadriceps 24, the patella 3 will get slightly displaced distally to a new position, marked as 3a. However, this will not affect its function.

(12) FIG. 3a shows fixation of the spacer 30 to the tibia 1 by means of a bone screw 37, just proximally to the insertion 36 of the ligament 35. The head 38 of the screw 37 should be well countersunk to avoid contact with the patellar ligament 35 which, with flexion, will wrap to a new position marked as 35a. The undersurface 39 facing the tibia bone should preferably be suitable for bony ongrowth or ingrowth.

(13) FIG. 3b shows an alternative method of fixation of the spacer 30 to the tibia 1 by means of an anchor 40. The anchor 40 is screwed into the bone with its conical head 41 left above the level of the bone. The spacer 30 is provided with a matching conical hole. The angle of the conical head and the hole should preferably be self-locking, e.g. 1:10 or 1:20. The bone facing surface 39 of the spacer 30 should preferably be suitable for bony ongrowth or ingrowth.

(14) FIG. 3c shows yet another method of fixation of the spacer 30 to the tibia 1 by means of at least one flange 50, which allows placement of a transverse screw 51 from the medial aspect of the tibia. A second flange could be fixed from the lateral side.

(15) Yet another method of fixation of the spacer 30 is shown on FIG. 3d using a staple-shaped fixation device 60.

(16) The surface 42 of the spacer 30 facing the ligament should be highly polished and resistant to wear. Titanium nitride or diamond-like coatings are suitable for that purpose.

(17) FIG. 4 shows a saggital view of a human knee with a spacer 130 inserted under the patellar ligament 105 to advance it from its original position 104. The spacer is fixed to the tibia 101. Patella 103 will be slightly displaced distally from its original position, marked as 103a, within the patellar groove 106 of the femur 102.

(18) FIGS. 5a-5c show orthogonal views of an embodiment of a spacer 130 for use in the human knee. The frontal view (FIG. 5a) shows a central section 131 and side sections, or flanges, 132, provided with holes 133 to accommodate bone screws. The top view (FIG. 5c) shows the central section 131 as being grooved, with the ridges 135 intended for guiding the patellar ligament. Side screws 134 can be comfortably placed into the tibial plateau, which in the human knee is much wider than in the dog knee. All of the bone facing surfaces 136 should be well adapted for bony ongrowth or ingrowth, while all of the ligament facing surfaces, e.g. 131 and 135, should be polished and preferably hard-coated for resistance to wear. Alternatively, ligament facing surfaces can be optimized for bony ongrowthin the final adaptation, the ligament would be sliding over a bone surface.

(19) While the primary indication of the invention is rupture of the ACL in human or CrCL in dog, it can also be used for partial ruptures of the same. It may also be used as a supportive measure for ACL repairs, as well as for intra-articular prosthesis or extra-articular sutures. It can also be used as a substitute for Maquet procedure for patello-femoral joint arthrosis.

(20) Spacers produced from artificial, biocompatible materials have advantages in terms of convenience of use and selection of sizes, but a surgeon could also use a piece of bone, autograft or allograft, appropriately shaped and fixed to the tibia to achieve the same result.

(21) The procedure of the present invention includes advancing the orientation of the patellar ligament to alter the relative angle with the tibial plateau. In an embodiment of the invention, the patellar ligament is advanced so that the relative angle with the tibial plateau is approximately 90 degrees when the knee is extended. In another embodiment of the invention, the patellar ligament is advanced so that the angle is decreased in the range of 10 to 30 degrees. In another embodiment of the invention, the patellar ligament is advanced so that the angle is decreased in the range of 5 to 15 degrees for a dog. In another embodiment of the invention, the patellar ligament is advanced so that the angle is decreased in the range of 10 to 30 degrees for a human. The patellar ligament may be advanced by inserting a spacer between the ligament and the tibia proximal to the insertion point of the ligament. The spacer may be fixed to the tibia.

(22) Having disclosed at least one embodiment of the present invention, various adaptations, modifications, additions, and improvements will be readily apparent to those of ordinary skill in the art. Such adaptations, modifications, additions and improvements are considered part of the invention which is only limited by the several claims attached hereto.