Evaluation of the mechanical properties of posterolateral structures and supporting posterolateral instability of the knee.

The objectives of this study are to evaluate the contributions of the popliteofibular ligament (PFL), the popliteus tendon (PT), and the lateral (fibular) collateral ligament (LCL) to the posterolateral stability of the knee by changing the sequence of selective transection. Twelve fresh-frozen cadaveric knees were divided into two groups. Group 1 has a cutting sequence as follows: PFL, PT, LCL. Group 2 has a cutting sequence as follows: PT, PFL, LCL. Each specimen was mounted on the apparatuses using the Ilizarov external fixator for measuring external rotatory and varus laxities at every 30 degrees from 0 degrees to 90 degrees of knee flexion. In both groups, there was no significant difference between the PFL and PT in the increment of respective external rotatory laxity after transection at each knee flexion angle, except 0 degrees in group 2. The transection of the LCL significantly increased the external rotation laxity at 0 degrees and 30 degrees . Varus instability was increased significantly only after cutting the LCL at every knee flexion angle. In conclusion, both the PFL and PT equally contribute to the external rotatory stability. The LCL also contributes to the external rotatory stability at early range of knee flexion. The LCL is a main structure for varus stability in the knee.