In situ forces in the posterolateral structures of the knee under posterior tibial loading in the intact and posterior cruciate ligament-deficient knee

The posterolateral structures of the knee consist of a complex anatomical a rchitecture that includes several components with both static and dynamic f unctions. Injuries of the posterolateral structures occur frequently in con junction with ruptures of the posterior cruciate ligament. To investigate t he role of the posterolateral structures in maintaining posterior knee stab ility, we measured the in situ forces in the posterolateral structures and the distribution of force within the structures' major components, i.e., th e popliteus complex and the lateral collateral ligament, in response to a p osterior tibial load. Eight cadaveric knees were tested. With use of a robo tic/universal force-moment sensor testing system, a posterior tibial load o f 110 N was applied to the knee, and the resulting five-degree-of-freedom k inematics were measured at flexion angles of 0, 30, 60, 75, and 90 degrees. The knees were tested first in the intact state and then after the posteri or cruciate ligament had been resected. These tests were also performed wit h an additional load of 44 N applied at the aponeurosis to simulate contrac tion of the popliteus muscle. In the intact knee, the in situ forces in the posterolateral structures were found to decrease with increasing knee flex ion. After the posterior cruciate ligament was sectioned, these forces incr eased significantly at all angles of flexion. With no load applied to the p opliteus muscle, the in situ forces-in the popliteus complex were similar t o those in the lateral collateral ligament. However, with a load of 44 N ap plied to the popliteus muscle, in situ forces in the popliteus complex were three to five times higher than those in the lateral collateral ligament. These results reveal that in response to posterior tibial loads, the poster olateral structures play an important role at full extension in intact knee s and at all angles of flexion in posterior cruciate ligament-deficient kne es. The popliteus muscle appears to be a major stabilizer under this loadin g condition; thus, the inability to restore its function may be a cause of unsatisfactory results in reconstructive procedures of the posterolateral s tructures of the knee.