In situ forces in the human posterior cruciate ligament in response to muscle loads: A cadaveric study

The objectives of this study were to determine the: effects of hamstrings a nd quadriceps muscle loads on knee kinematics and in situ forces in the pos terior cruciate ligament of the knee and to evaluate how; the effects of th ese muscle loads change with knee flexion. Nine human cadaveric knees were studied with a robotic manipulator/universal force-moment sensor testing sy stem. The knees were subjected to an isolated hamstrings load (40 N to both the biceps and the semimembranosus), a combined hamstrings and quadriceps load (the hamstrings load and a 200-N quadriceps load), and an isolated qua driceps load of 200 N. Each load was applied with the knee at full extensio n and at 30, 60, 90, and 120 degrees of flexion. Without muscle loads, in s itu forces in the posterior cruciate ligament were small, ranging from 6 +/ - 5 N at 30 degrees of flexion to 15 +/- 3 N at 90 degrees. Under an isolat ed hamstrings load, the in situ force in the posterior cruciate ligament in creased significantly throughout all angles of knee flexion, from 13 +/- 6 N at full extension to 86 +/- 19 N at 90 degrees. A posterior tibial transl ation ranging from 1.3 +/- 0.6 to 2.5 +/- 0.5 mm was also observed from ful l extension to 30 degrees of flexion under the hamstrings load. With a comb ined hamstrings and quadriceps load, tibial translation was 2.2 +/- 0.7 mm posteriorly at 120 degrees of flexion but was as high as 4.6 +/- 1.7 mm ant eriorly at 30 degrees. The in situ force in the posterior cruciate ligament decreased significantly under this loading condition compared with under a n isolated hamstrings load, ranging from 6 +/- 7 to 58 +/- 13 N from 30 to 120 degrees of flexion. With an isolated quadriceps load of 200 N,the in si tu forces in the posterior cruciate ligament ranged from 4 +/- 3 N at 60 de grees of flexion to 34 +/- 12 N at 120 degrees. Our findings support the no tion that, compared with an isolated hamstrings load, combined hamstrings a nd quadriceps loads significantly reduce the in situ force in the posterior cruciate ligament. These data are in direct contrast to those for the ante rior cruciate ligament. Furthermore, we have demonstrated that the effects of muscle loads depend significantly on the angle of knee flexion.