Purpose: To determine the involvement of the posterolateral structures including the lateral collateral ligament, the popliteus muscle-tendon unit, the arcuate ligament (popliteofibular ligament, fabellofibular ligament, popliteomeniscal fascicles, capsular arm of short head of the biceps femoris and anterolateral ligament) and the posterior cruciate ligament in providing restraint to excessive recurvatum, tibial posterior translation and external tibial rotation at 90° of flexion.
Methods: Ten fresh-frozen cadaveric knees were tested with dial test, posterior drawer test and recurvatum test. The values were collected, using a surgical navigation system, on intact knees, following a serial section of the posterolateral corner (lateral collateral ligament, arcuate ligament and popliteus muscle-tendon unit), followed by the additional section of the posterior cruciate ligament.
Results: The mean tibial external rotation, recurvatum and posterior drawer were, respectively, measured at 9° ± 4°, 2° ± 3° and 9 ± 1 mm on intact knees. These values increase to 12° ± 5°, 3° ± 2° and 9 ± 1 mm after cutting the lateral collateral ligament; 17° ± 6° (p < 0.05), 3° ± 2° and 10 ± 1 mm after sectioning the arcuate ligament; 18° ± 7°, 3° ± 2° and 10 ± 1 mm after sectioning the popliteus muscle-tendon unit and 27° ± 6° (p < 0.05), 5° ± 3° (p < 0.05) and 28 ± 2 mm (p < 0.05) after the additional section of the posterior cruciate ligament.
Conclusion: Among the different structures of the posterolateral corner, only the arcuate ligament has a significant role in restricting excessive primary and coupled external rotation. The popliteus muscle-tendon unit is not a primary static stabilizer to tibial external rotation at 90° of knee flexion. The posterior cruciate ligament is the primary restraint to excessive recurvatum and posterior tibial translation. The posterior cruciate ligament and the arcuate ligament have predominant role for the posterolateral stability of the knee. The functional restoration of these ligaments is an important part of the surgical treatment of posterolateral ligamentous injuries.