Anterior cruciate ligament replacement: a review

The anterior cruciate ligament (ACL) is the major intra-articular mechanical element that limits motion of the tibia with respect to the femur. It is a multi-fasciculated structure composed of crimped aligned collagen fibers. The purpose of this paper is to review the literature on ACL structure and mechanical properties in an effort to stimulate the development of a new generation of more effective replacement devices. Replacement of the ACL is achieved using biologic and synthetic grafts. Biologic grafts include illiotibial band, semitendinosus and gracilis tendons, patellar tendon, and meniscus. Bone-patellar-bone complexes used to replace the ACL are revascularized and ultimately replaced by neo-ligament. Synthetic implants including the Integraft, Leads-Keio ligament, Gore-Tex¿ ligament and Kennedy Ligament Augmentation Device (LAD) have either not been approved or approved by the FDA for limited use as a replacement for the ACL. The Kennedy LAD has been found to increase the strength of autogenous tissue during revascularization. Based on the success of autografts and the Kennedy LAD, we conclude that the next generation of ACL replacement devices will consist of a scaffold and a biodegradable augmentation device. The scaffold will have a structure that mimics the normal ACL as well as stimulates revascularization and healing. A biodegradable augmentation device will be employed to mechanically reinforce the scaffold without stress shielding the neo-ligament. By combining the advantages of autografts and a biodegradable augmentation device, a new generation of ACL replacements will be achieved.