THE EFFECTS OF A POPLITEUS MUSCLE LOAD ON IN-SITU FORCES IN THE POSTERIOR CRUCIATE LIGAMENT AND ON KNEE KINEMATICS - A HUMAN CADAVERIC STUDY

To investigate the effect of simulated contraction of the popliteus mu scle on the in situ forces in the posterior cruciate ligament and on c hanges in knee kinematics, we studied 10 human cadaveric knees (donor age, 58. to 89 years) using a robotic manipulator/universal force mome nt sensor system. Under a 110-N posterior tibial load (simulated poste rior drawer test), the kinematics of the intact knee and the in situ f orces in the ligament were determined. The test was repeated with the addition of a 44-N load to the popliteus muscle. The posterior cruciat e ligament was then sectioned and the knee was subjected to the same t ests. The additional popliteus muscle load significantly reduced the i n situ forces in the ligament by 9% to 36% at 90 degrees and 30 degree s of flexion, respectively. No significant effects on posterior tibial translation of the intact knee were found. However, in the ligament-d eficient knee, posterior tibial translation was reduced by up to 36% o f the translation caused by ligament transection. A coupled internal t ibial rotation of 2 degrees to 4 degrees at 60 degrees to 90 degrees o f knee flexion was observed in both the intact and ligament-deficient knees when the popliteus muscle load was added. Our results indicate t hat the popliteus muscle shares the function of the posterior cruciate ligament in resisting posterior tibial loads and can contribute to kn ee stability when the ligament is absent.