Popliteus Bypass and Popliteofibular Ligament Reconstructions Reduce Posterior Tibial Translations and Forces in a Posterior Cruciate Ligament Graft

Abstract

To measure the abilities of popliteus tendon (POP) and popliteofibular ligament (PFL) graft reconstructions to limit posterior tibial translations and alter forces in a PCL graft reconstruction after posterior cruciate ligament (PCL) and lateral collateral ligament (LCL) reconstruction. Fifteen fresh frozen cadaveric knees underwent anterior-posterior (AP) laxity testing with 200 N of applied anterior and posterior tibial force. Forces in the native PCL were recorded during passive extension from 120 degrees to 0 degrees with an applied 100-N posterior tibial force. The popliteus tendon was released at its femoral origin, the PFL and LCL were cut, and the PCL was sectioned, creating a combined grade 3 PCL and posterolateral corner injury. The PCL was reconstructed with a single-bundle inlay graft tensioned to restore intact knee laxity to within 1 mm at 90 degrees , and the LCL was reconstructed with an anatomically placed graft. Testing was repeated with POP and PFL posterolateral reconstructions in addition to the PCL and LCL reconstructions. PCL + LCL grafts alone matched intact knee laxities between 20 degrees and 90 degrees of flexion; mean laxity was 3.5 mm greater than intact at 0 degrees and 2.2 mm greater at 10 degrees. The addition of a POP reconstruction to PCL + LCL reconstructions significantly reduced AP laxities from -2.4 mm (0 degrees flexion) to -1.4 mm (90 degrees flexion). Mean laxities with POP and PFL grafts were not significantly different from the intact knee or from each other. Mean PCL graft forces with the PCL + LCL reconstructions alone were not significantly different than those with the native PCL. Mean PCL graft forces with POP and PFL reconstructions were not significantly different from each other; both means were significantly less than those for the PCL + LCL reconstructions alone at flexion angles greater than 55 degrees. After PCL and LCL reconstruction, the popliteus bypass and popliteofibular ligament reconstructions not only eliminated excessive posterior laxity and returned the knee to a normal laxity profile but also resulted in substantial decreases in PCL graft forces. These results provide further rationale for reconstructing torn posterolateral structures with a grade 3 posterolateral injury in combination with a PCL reconstruction.