Effects of posterolateral reconstructions on external tibial rotation and forces in a posterior cruciate ligament graft.

BACKGROUND

In patients with a Grade-3 injury, reconstructions of the lateral collateral ligament, popliteus tendon, and popliteofibular ligament are commonly performed in conjunction with a reconstruction of the posterior cruciate ligament. The objectives of this study were (1) to compare the abilities of three types of posterolateral graft reconstruction to restrain external tibial rotation and alter forces in a posterior cruciate graft and (2) to compare tibial rotations and posterior cruciate graft forces associated with two levels of initial posterolateral graft tension.

METHODS

Forces in the posterior cruciate ligament were recorded as the knee was extended from 120 degrees to 0 degrees and a 5-N-m external tibial torque was applied. The posterior cruciate ligament was reconstructed, and external tibial rotation and the forces in the posterior cruciate graft were recorded. These measurements were again recorded after sectioning of the posterolateral structures and after reconstruction of the lateral collateral ligament, alone as well as in combination with reconstruction of the popliteus tendon and in combination with reconstruction of the popliteofibular ligament.

RESULTS

With the lateral collateral ligament intact, removal of the popliteus tendon from its femoral origin significantly increased external tibial rotation. Applying tension to a popliteus or popliteofibular graft internally rotated the tibia, with no significant difference between the rotations caused by the tensioning of the two grafts. Tibial rotation was significantly greater when graft tensioning had been performed with the tibia free to rotate than it was when the tensioning had been done with the tibia locked in neutral rotation. With an applied external tibial torque, a reconstruction of the lateral collateral ligament alone was not sufficient to reduce posterior cruciate graft forces to normal. The addition of a popliteus or popliteofibular reconstruction to the lateral collateral ligament reconstruction significantly reduced posterior cruciate graft forces to normal (or below normal) levels. The external rotations associated with these two combined reconstructions were equivalent and significantly less than that in the intact knee. Increasing tension in either the popliteus or the popliteofibular graft from 10 to 30 N significantly decreased external rotation.

CONCLUSIONS

The posterolateral grafts acted to resist applied external torque, thereby off-loading the posterior cruciate graft. Popliteus and popliteofibular grafts were more favorably aligned than a lateral collateral ligament graft to resist external rotation, and they had similar effects.