The biomechanics and function of the secondary restraints to the anterior cruciate ligament.

The primary function of the anterior cruciate ligament has been described as one of restraining anterior motion of the tibia. The passive structures that offer secondary support for the anterior cruciate ligament are the collateral ligaments, the mid-third capsular ligaments, the menisci, and the iliotibial band. In this article, the biomechanics and function of these structures, as well as their effectiveness in providing back-up support for the anterior cruciate ligament, are discussed.