On the Interpretation of Our Anterior Cruciate Ligament Data

Design of a synthetic replacement or selection of a biologic substitute requires detailed knowledge of the mechanical properties of the normal ligament. Femur-anterior cruciate ligament-tibia unit (ACL) data have been frequently used for this purpose, although not always properly. Mechanical properties of the human ACL-bone unit are reviewed. Ligament stiffness, elongation, and energy results are based on grip-to-grip motion and thus include ligament and limited bone deformations. Maximum bone-ligament-bone force in young donors (1730 +/- 66N) is higher than reported previously and represents only ligamentous failures. Methods for measuring tissue dimensions are provided and must be duplicated for obtaining accurate material property data. Bone-ligament-bone strain data are higher than those in reports where midsubstance collagen strains are measured and differ from data obtained on isolated ligaments. The authors have examined many factors that affect ligament-bone unit response. Increasing age weakens the tissue-bone preparation, and only when testing is performed at high rates will ligamentous failures predominate. Use of the authors' data in prosthetic ligament evaluation requires that the material be selected based on ligament bundle properties, the prosthesis be examined under similar testing conditions, and anticipated functional loads and margins of safety be determined.