Orthopaedic Review

Savio L-Y Woo, Ph.D., Glen A. Livesay, M.S., and C. Engle, M.D.


The anterior cruciate ligament (ACL), one of the major stabilizers of knee motion, is both anatomically and functionally complex. Mid-substance tears of the ACL often require surgical reconstruction to restore knee stability and approximate normal knee kinematics. However, there is still a great deal of debate concerning graft selection, reconstruction technique and post-operative rehabilitation. This review will discuss the biomechanical aspects of this important clinical problem, and will describe a series of experiments designed to investigate the structural properties of the ACL and also explore its role in the kinematics of the normal knee. The first study establishes baseline data for the load-elongation of the human femur - anterior cruciate ligament tibia (FATC) complex, including linear stiffness, ultimate load, and energy absorbed to failure as a function of age. Second, we have developed a new methodology to measure the in-situ lengths and forces within the ACL during passive knee flexion and extension and also under the application of external loads. Further, the stabilizing effects of the quadriceps and hamstrings muscles, as well as the effects of ACL deficiency on knee kinematics were examined. Finally, methods of ACL reconstruction were studied with emphasis on evaluating the role of graft placement and initial graft tension on the resultant graft force and knee function.