Codominance of the individual posterior cruciate ligament bundles. An analysis of bundle lengths and orientation

BACKGROUND: It is unclear how each bundle of the posterior cruciate ligament contributes to posterior knee stability. HYPOTHESIS: Changes in bundle orientation and length occur such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. STUDY DESIGN: Controlled laboratory study. METHODS: Six fresh-frozen cadaveric knees were studied in a joint-testing rig with individual quadriceps and hamstring muscle loading. Kinematic data for the tibia and femur were obtained at knee flexion angles from 0 degrees to 120 degrees. The joint was then disarticulated, and the insertions of the two bundles on the tibia and femur were digitized. RESULTS: Length of the anterolateral bundle increased with increasing knee flexion angle from 10 degrees to 120 degrees. Length of the posteromedial bundle decreased with increasing knee flexion angle from 0 degrees to 45 degrees and increased slightly from 60 degrees to 120 degrees. Length of the anteromedial bundle was significantly less than that of the posteromedial at 0 degrees, 10 degrees, and 20 degrees of knee flexion. The anterolateral bundle was significantly more horizontal at flexion angles of 0 degrees, 10 degrees, 20 degrees, 30 degrees, and 45 degrees (P < 0.05). The posteromedial bundle was more horizontal at 120 degrees. CONCLUSIONS: Changes in orientation take place such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. CLINICAL RELEVANCE: Double-bundle reconstructions achieve more physiologic knee function.