Ten dogs and six rhesus monkeys underwent transection and repair of the anterior cruciate ligament. One-half of the procedures involved the femoral end, the other half involved the tibial end of the ligament. Seven of the 10 canine and all of the primate ligaments, that had been transected and repaired, did heal. Functional and clinical instability was demonstrable in all repaired knees. The monkeys developed fewer degenerative changes with more grossly normal appearing ligaments after the repairs than did the dogs. Failure testing on an Instron materials testing machine revealed maximum strength of the repaired ligaments to be 10.4% for the repairs at the femoral end and 2.0% for repairs at the tibial ends in dogs when compared with the contralateral control knees. In monkeys the femoral repairs were 46.8% and the tibial repairs were 62.6% of the control knees. Inadequate immobilization and early stress were believed to be principal causes of the poorer results in dogs. The observations in monkeys support the suggestion that injured anterior cruciate ligaments that can be repaired, should be repaired.

Seventy-five rats were divided into a control and four exercise groups of differing frequency and duration. After 8 weeks of endurance-type exercise on a motorized treadmill, the rats were sacrificed and the anterior cruciate ligaments were tested to failure on an Instron materials testing machine at a strain rate of 95% sec-1. Of the 121 ligaments tested, 119 failed by pure interstitial failure. There was significant increase in both the strength and stiffness of the anterior cruciate ligaments in the exercised rats but those rats exercised more frequently (daily vs. every other day) and for shorter duration (30 min rather than 60 min) had the greatest increase in strength. This study has shown that endurance-type exercise is beneficial to the anterior cruciate ligament as both strength and stiffness are increased and functionally the ligament remains unchanged by exercise.

Eleven dogs underwent transection of the anterior cruciate ligament at the femoral origin of the stifle (knee) joint. The anterior cruciate ligaments were repaired in a conventional manner and augmented by transferring the medial one-third of the patellar tendon and inserting it into the lateral femoral condyle. The repairs were evaluated either 4 or 8 months postoperatively. All repaired and augmented anterior cruciate legaments in this series healed satisfactorily to provide clinical and functional stability to the knee joints. Instron testing of the repaired and augmented anterior cruciate ligaments showed maximum strength at 4 months of 46.2 +/- 10.9 kgf and at 8 months of 64.3 +/- 14.3 kgf as compared to the control of 122.7 +/- 11.6 kgf. Histologic evaluation showed that by 8 months the repaired and augmented anterior cruciate ligaments had healed by bony ingrowth. Thus, interstitial failure occurred during Instron testing. The transferred patellar tendon provided additonal blood supply, splinted the anterior cruciate ligament to allow healing, and increased the strength of the repaired complex.

The anterior cruciate ligament was transected at the femoral origin in the knee joint of 12 dogs. The ligaments were repaired in a conventional manner and reinforced with a polyglycolic acid (PGA) ligament of braided Dexon (Davis & Geck, Pearl River, NJ) suture. At two weeks the PGA ligament was still providing excellent support for the healing anterior cruciate ligament, and there was no synovitis within the knee joint. After five weeks, initial healing had firmly attached the repaired anterior cruciate ligament to the femoral condyle, and the PGA ligament had resorbed without inflammatory or fibrotic response. All repaired and reinforced ligaments in this series healed and provided functional stability to the knee joints. Biomechanical testing of the repaired anterior cruciate ligaments at four months produced a maximum strength of 54.2 +/- 6.3 kgf. Sulfur-35 uptake showed viable active collagen-producing cells in the repaired ligaments four months postoperatively. Thus, the biodegradable PGA ligament reinforced and splinted successfully the repaired anterior cruciate ligament.

In an effort to determine the healing potential of medial meniscus tears, 20 canine and 12 rhesus knee joints were subjected to transverse medial meniscus laceration and repair with a single Dexon suture (Davis & Geck, Pearl River, NY). At four months, 12 out of 32 (38%) had healed completely with restoration of the inner meniscal rim and 18 (56%) showed partial healing sufficient to protect the underlying articular cartilage. Only 2 (6%) of the menisci failed to heal. Histologic evaluation showed that the scar tissue present in the menisci was composed of unorganized collagen without common ground substance components. As a result of these studies, we believe that certain meniscal tears, particularly those involving the vascular periphery, can heal and may be repaired rather than treated by meniscectomy.