In vivo and in vitro investigation of the long-term behavior and fatigue strength of carbon fiber ligament replacement.

The long-term behavior of carbon fiber ligament replacements was evaluated in sheep. In vitro assessments of both isolated carbon fiber prostheses and resected animal ligaments were performed. The right knee in 45 sheep was reconstructed. In 30 animals, only the medical collateral ligaments were replaced, but with different systems of anchorage to bone. In 15 animals, a combined replacement of medial collateral ligament and anterior cruciate ligament was performed. In the first group the animals were sacrificed three months postoperation, while in the latter group evaluation was performed one year after surgery. After one year the strength of the medial collateral ligament complex was higher than that of the normal sheep ligaments. The elasticity and extensibility were similar to those of the normal ligaments. No case of partial rupture or rupture of the medial collateral ligament replacements was seen, but four of 12 anterior cruciate replacements showed signs of partial rupture. In vitro testing showed that rupture is more likely to occur where movement occurs around a small radius of bending, and this may be a factor in these cases where the anterior cruciate ligament enters a bony tunnel at an acute angle. Histologic assessment showed good biocompatibility, similar to that reported by other authors. With an operative technique designed to increase the radius of bending where the carbon fiber enters bone, these ligament replacements have a fatigue strength and elasticity adequate for long-term survival.