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The Effects of Varied Joint Motion and Loading Conditions on Posterior Cruciate Ligament Fiber Length Behavior

Dana C. Covey, MD^*,, Alexander A. Sapega, MD and Robert C. Marshall, MD

From the US Naval Hospital, Okinawa, Japan, the Pennsylvania Knee and Shoulder Center, King of Prussia, Pennsylvania, and the Headquarters of the Third Marine Expeditionary Force, Okinawa, Japan

^* Address correspondence to CAPT Dana C. Covey, MD, MC, USN, Department of Orthopaedics, Naval Medical Center, 38000 Bob Wilson Drive, San Diego, CA 96362-2563 (e-mail: coveydc{at}oki10.med.navy.mil).

Background: The posterior cruciate ligament has been described as being composed of 2 bands that reciprocally tighten and loosen with knee flexion, but the fiber anatomy and behavior may be more complex.

Hypothesis: The mechanical effects of defined loading conditions at discrete knee joint angles can vary significantly within the substance of the posterior cruciate ligament depending on the fiber region tested.

Study Design: Controlled laboratory study.

Methods: Nine intact, fresh-frozen cadaveric knees were instrumented with excursion filaments implanted within 4 fiber regions of the posterior cruciate ligament. Patterns of fiber behavior were analyzed as a function of the variable linear separation distance between tibial and femoral fiber attachment sites during joint motion under a simulated quadriceps contraction, tibial internal rotation, and tibial external rotation. Analysis of variance, the Newman-Keuls multiple comparisons procedure, and paired t tests were used to evaluate statistical significance.

Results: Compared with the control pattern of fiber behavior during unloaded passive knee motion from 0° to 120°, the quadriceps force caused loosening of most ligament fibers at knee flexion of less than 75°. Tibial internal rotation significantly slackened the anterior and central fiber regions near extension and significantly tightened the central and posterior fiber regions with progressive flexion. External rotation had an effect similar to internal rotation on the anterior and central fiber regions but caused significant slackening of the posterior fiber regions from 0° to 45°.

Conclusions: Distinct geographic regions within the posterior cruciate ligament have different functional roles depending on the joint angle and the type of load to which the knee is subjected.

Clinical Relevance: The specific graft placement parameters in a given surgical procedure relate to end-to-end length changes of the graft and may have important implications for postoperative rehabilitation and return to specific functional activities.

Key Words: posterior cruciate ligament (PCL) • joint loading • biomechanical • fiber region • knee