01783-A: Mechanical strength of three patella-ligament-tibia allograft fixation techniques for ruptured cranial cruciate ligament repair
Grant Status: Closed
Project SummaryThe cranial cruciate ligament (CCL) is one of the main stabilizing ligaments of the knee and equivalent to the ACL in humans. Rupture of the CCL is the most common cause of limping in dogs and over $1.2 billion/year is spent on treatment in the U.S. Research has supported that surgery provides dogs with the best chance of return to pre-injury activity. However, none of the surgical procedures that are currently performed for RCCL in dogs reproduce the anatomy or mechanical duties of the normal CCL; this is one explanation why nearly all dogs get progressive arthritis even with surgery. The most common surgical repairs for people replace the ACL with a donor ligament. Our previous work demonstrated the suitability of the whole patella ligament (PLT; knee cap-ligament-bony attachment) as a graft in dogs. Strength testing showed that the PLT had similar strength to a normal CCL in dogs of similar size. The objective of this project is to test surgical techniques for dogs that mimic all functions of the CCL in hopes of decreasing postoperative arthritis. One technique secured the ligament in a femoral and tibial tunnel using a biocompatible interference screw. The second technique assessed secured the ligament on the femur in a similar fashion. The patella was left on the ligament and past through a narrowing hole to secure the ligament to the tibia. Eighteen specimens were successfully tested through cycling (repeated testing at a small weight to simulate walking) and load to failure (testing until it breaks). Load values were taken at set points 3, 5 and 10 mm of forward movement of the tibia. These set points were chosen based off of previous research that should a normal CCL can have up to 3 mm of elongation. Also, clinically, cranial drawer (a test looking for a ruptured CCL) can likely be consistently detected with 10 mm of greater of cranial tibial translation. The intact CCL group had an average load of 542.9, 908.9 and 1647.7 N at 3, 5 and 10mm displacement respectively. In group 1, ligament fixation with 1 interference screw, had an average load of 203, 362.7 and 720 N at 3, 5 and 10mm respectively. In group 2, with double fixation with interference screws, average load was 219, 325.6 and 650.3 N at 3, 5 and 10 mm respectively. It has been reported that during a walk, the canine CCL resists 50 N of force and at vigorous play loads are between 400-600 N. These data, and data from our initial study, suggest that for a 25-kg dog daily use loads may approach 600N. Therefore, the two repairs in this procedure would likely resist the forces encounter at a walk but likely elongate to around 10mm if the patient were to sustain more vigorous activity during the recovery period. The stiffness of the 2 repairs and intact CCL were also compared. The stiffness of the intact CCL was 184 N/mm compared to 86 and 67 N/mm for group 1 and 2, respectively. Looking at previous work by the authors, the stiffness of the PLT ligament is similar to that of the CCL. This suggests the fixation is the weakest point of the repair. Looking at group 1, all specimens failed by pull out of the ligament from the femur. Group 2 had 4 failures by ligament pull out from the femur and 2 failed by pull out from the tibia. No specific reason was identified why failure occurred on the femur versus the tibia. In summary, neither repair was able to replicate the strength of the intact CCL, although both repairs achieved the goal of 33% the strength of the intact CCL. Both repairs would likely be strong enough during the recovery period if the patient were restricted. Further development of the repairs will likely continue to increase their strength. Technical improvements may include use of a stop bead on the ligament ends, filling a greater percentage of the drill hole with ligament, use of a different interference screw. At this time it is recommended that further development of the repairs and testing continue before considering placemen
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