Posterolateral Knee
The goal of this study was to determine if untreated grade III injuries of posterolateral knee structures (PLS) contribute to increased force on a PCL reconstructed graft. This was accomplished through measuring the force in the PCL graft during joint loading for a PCL reconstructed knee with otherwise intact structures, and in the same knee with the PCL reconstructed after selected cutting of specific posterolateral knee structures. Eight fresh frozen cadaveric knees were utilized. A PCL reconstruction using a quadriceps tendon graft was performed. The bone block portion of the graft was secured to the femur with an interference screw. The tibial end of the graft was fixed to a tensioning jig (on the posterior tibia) via a load cell used to measure the force in the graft. The knee was then mounted in a knee-testing machine, and an instremented spatial linkage (ISL) was applied to measure 6 degrees -of-freedom motion. The graft force was standardized to the force remaining in the graft after fixation while an 89 N (20-lb.) distal traction load was applied to the tibial portion of the graft with the knee in 90 degrees of knee flexion (as would be done clinically). Joint loading was then performed. Loads applied were 67 N of posterior load. 5 Nm of internal and external tibial torque, 12 Nm of varus and valgus moment, and 67 N posterior load coupled with 5 Nm external tibial torque. Testing was repeated 3 times at each flexion angle (30o, 60o, and 90o) and the results averaged. PCL reconstruction and tests were first performed on the knee with the PLS intact, and then after sequential individual sectioning of the popliteofibular ligament, popliteus tendon, and the fibular collateral ligament. The PCL graft force was significantly higher with the PLS transected during varus loading at 30o (p<0.02), 60o (p<0.02), and 90o (p<0.02) degrees of flexion than it was for the same loading of the intact joint. In addition, coupled loading of posterior drawer and external tibial torque at 30o (p<0.05), 60o (p<0.01), and 90o (p<0.002) degrees increased graft force. There was no significant increase in force on the PCL graft for any cutting cycle at any knee flexion angle for a posterior force, valgus force, or internal and external tibial torque. In conclusion, we found that during joint loading a significant increase in force on a PCL graft occurred during varus and coupled posterior drawer and external tibial torque in knees with grade III PLS deficiency compared to the same reconstruction in the intact knee. We believe that this study verifies the clinical observation that untreated grade III PLS injury contributes to PCL graft failure by developing higher forces on the PCL graft. It is recommended that grade II PLS injuries with evidence of varus and/or coupled posterior- external ration instability be repaired/ reconstructed at the time of PCL reconstruction to decrease the chance of postreconstruction PCL graft failure.
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