Anterior cruciate ligament replacement with polyester fibre. A long-term study of tissue reactions and joint stability in sheep.

We excised the anterior cruciate ligament from the left stifle of 24 sheep and replaced it by a polyester fibre implant routed 'over the top' of the femoral condyle and fixed, using grommets and screws. All the joints were sound, and the animals moved normally until they were killed at six, 12 and 24 months after operation. We found that the implants were always covered by host tissue, which matured into bundles with a histological appearance similar to the natural ligament. The implants were joined to the bones by organised fibrous tissue and there was no anchorage loosening. There was no synovitis, but the operated joints showed progressive cartilage degeneration. The reconstructed joints became less stable immediately after operation, but regained normal stability as the neoligaments developed. The neoligaments lost strength with time, despite tissue ingrowth. The good functional, biomechanical, and histological results justify clinical trials of this type of implant.

The effect of induced electric currents on bone after experimental osteotomy in sheep.

We have investigated the effect of currents induced by electromagnetic fields on the healing of the tibia of sheep after osteotomy, using objective and quantifiable criteria wherever possible. A battery-powered, induction apparatus was developed and was enclosed within the cast applied to the limb, so that the treated fractures received pulsed magnetic fields for 24 hours a day while the animals were freely mobile. In all, 13 sheep were treated and 13 were used as controls. The response was assessed by radiography of the limb and of the excised bone, by histology, including measurement of the areas of callus, fibrocallus and cortical bone, and by measurement of the uptake and extraction of bone-seeking mineral. All the bones healed and no statistically significant differences between the treated animals and the controls were discovered except (at only P less than 0.05) in the uptake of bone-seeking mineral; this increased more rapidly in treated animals over the two to three weeks after osteotomy, although at six weeks the uptake in both groups was the same.

Cranial cruciate stability in the rottweiler and racing greyhound: an in vitro study.

An in vitro biomechanical study of cadaver stifles from rottweilers and racing greyhounds was undertaken to evaluate the contribution of the cranial cruciate ligament to stifle joint stability. This was performed at differing stifle joint angles, first with the joint capsules and ligaments intact and then with all structures removed except for the cranial cruciate ligament. Craniocaudal laxity increased in both breeds as stifle flexion increased. The rottweiler stifle showed greater craniocaudal joint laxity than the racing greyhound at all joint angles between 150 degrees and 110 degrees, but the actual increases in joint laxity between these joint angles were similar for both breeds. Tibial rotation during craniocaudal loading of the stifle increased craniocaudal laxity in both breeds during joint flexion. The relative contribution of the cranial cruciate ligament to cranial stability of the stifle joint increased as the joint flexed and was similar in both breeds.

Comparison of the biomechanical properties of rottweiler and racing greyhound cranial cruciate ligaments.

An in vitro study of rottweiler and racing greyhound cranial cruciate ligaments revealed that the rottweiler ligaments had a significantly greater cross-sectional area at their distal attachments. Mechanical testing showed that the ultimate load related to body mass was significantly higher in the extended racing greyhound stifle during cranial tibial loading to failure, as were linear stiffness, tensile strength and tangent modulus. During ligament axis loading to failure, the only significant difference in structural and mechanical properties recorded between the two breeds was a greater ultimate strain for the greyhound ligament with the stifle joint flexed. Energy absorbed by the ligament complex at failure during cranial tibial loading was twice that for ligament axis loading for both breeds. The clinical significance is that the rottweiler cranial cruciate ligament is more vulnerable to damage as it requires half the load per unit body mass that the greyhound requires to cause a rupture.

Synovial cysts in cats.

The clinical and radiographic appearance and histological findings in three cats with cystic extensions of the elbow joint capsule are described. The condition was only temporarily alleviated by surgical excision or drainage. In all cases the condition was associated with osteoarthritis.

A comparative study of single- and double-bundle ACL reconstructions in sheep.

Work in vitro has previously shown superior restoration of knee stability using a double-bundle anterior cruciate ligament (ACL) reconstruction compared with single bundles taken through the condyle or 'over the top'. This paper describes an animal study designed to compare the three ACL reconstructions in vivo, in order to collect data that could support the clinical use of a double-bundle reconstruction. The three methods were compared in three groups of eight sheep, the ovine ACL having a distinct double-bundle structure. Biomechanically matched polyester fibre implants were used, with 6 months in vivo. The three methods led to similar intra-articular fibrous tissue integration of the implants and no evidence of implant damage, and biomechanical testing found greater laxity than normal for all three groups. The double-bundle group, however, had more joint surface degeneration than the other groups. It was concluded that clinical use of the double-bundle reconstruction was not indicated by the results of this experiment, in view of the more complex surgery and lack of superior performance.