Abstract
BACKGROUND: In vitro data suggest that injury to the posterior cruciate ligament stresses the posterolateral structures of the knee, placing them at greater risk of secondary injury. However, it is not known how isolated posterior cruciate ligament deficiency affects these soft tissue stabilizers of the knee joint in vivo. HYPOTHESIS: Posterior cruciate ligament deficiency will alter the apparent length patterns of the lateral collateral ligament (LCL) and popliteus. STUDY DESIGN: Controlled laboratory study. METHODS: The apparent length changes in the lateral collateral ligament and popliteus muscle-tendon unit during weightbearing knee flexion were studied in 14 patients with isolated, unilateral posterior cruciate ligament deficiency using magnetic resonance imaging, dual-orthogonal fluoroscopy, and 3-dimensional modeling. Data of the injured and uninjured contralateral sides were compared. RESULTS: Posterior cruciate ligament deficiency caused significant increases in the apparent length of both posterolateral structures (P < .05). The differences between injured and uninjured contralateral side were greatest at 120 degrees of knee flexion in the lateral collateral ligament (48.2 +/- 6.1 mm and 51.6 +/- 6.1 mm, respectively) and at 30 degrees of knee flexion in the popliteus (101.2 +/- 9.3 mm and 110.4 +/- 10.2 mm, respectively). CONCLUSION: Deficiency of the posterior cruciate ligament alters the length patterns of posterolateral structures in vivo and might place them at greater risk of secondary injury. CLINICAL RELEVANCE: Reestablishment of normal kinematics after posterior cruciate ligament injury is critical for restoring normal function of posterolateral structures of the knee.