The Biocompatibility of Nitinol in Knee Joint Spaces and Femoral Tunnels: An Experimental Study in Rats

Currently the most common method of reconstructing a ruptured anterior cruciate ligament (ACL) is by using bone-patellar tendon-bone (BPTB) or semitendinosus, gracilis tendon autografts. Although good results are reported, donor morbidity continues to be a problem. To overcome these complications, synthetic grafts have been investigated. However, to date no prosthetic graft has been developed as an alternative to patellar or hamstring tendon autografts. The aim of the present study was to assess the biocompatibility of nitinol in rat knee joint spaces and distal femoral bones. Ten male, healthy Wistar albino rats, weighing between 300-350 g, were used. The right knee joint of each rat was reached by medial longitudinal parapatellar dissection. The femur distal was penetrated by a size 0.5 mm of Kirshner wires. Twenty nitinol wires were placed in the bone tunnel (0.125 mm in diameter and 5 mm long). In addition one nitinol wire was placed in the joint space. Following hemostasis, the layers were closed with interrupted sutures. The same procedure was repeated for the left side without placing any nitinol wire. The rats were allowed unrestricted weight bearing. Two animals died of unknown reasons during follow-up. The remaining rats were sacrificed 8 weeks after surgery. The knees were removed by careful dissection and the nitinol wires were removed. The sections taken from these specimens were stained with standard hematoxylin and eosin and with Mason trichrome and examined under the light microscope. The bone tunnels were filled with osteocytes and chondrocytes. In two specimens of the nitinol group, moderate synovitis was detected. The synovitis rate in the study group was found to be statistically insignificant. In conclusion, the short term biocompatibility of nitinol in the rat knee joint space and femoral tunnel was found to be within acceptable limits.