Strain in the human medial collateral ligament during valgus loading of the knee

The medial collateral ligament is one of the most frequently injured ligame nts in the knee. Although the medial collateral ligament is known to provid e a primary restraint to valgus and external rotations, details regarding i ts precise mechanical function are unknown. In this study, strain in the me dial collateral ligament of eight knees from male cadavers was measured dur ing valgus loading. A material testing machine was used to apply 10 cycles of varus and valgus rotation to limits of +/- 10.0 N-m at flexion angles of 0 degrees, 30 degrees, 60 degrees, and 90 degrees. A three-dimensional mot ion analysis system measured local tissue strain on the medial collateral l igament surface within 12 regions encompassing nearly the entire medial col lateral ligament surface. Results indicated that strain is significantly di fferent in different regions over the surface of the medial collateral liga ment and that this distribution of strain changes with flexion angle and wi th the application of a valgus torque. Strain in the posterior and central portions of the medial collateral ligament generally decreased with increas ing flexion angle, whereas strain in the anterior fibers remained relativel y constant with changes in flexion angle. The highest strains in the medial collateral ligament were found at full extension on the posterior side of the medial collateral ligament near the femoral insertion. These data suppo rt clinical findings that suggest the femoral insertion is the most common location for medial collateral ligament injuries.