Effects of applied quadriceps and hamstrings muscle loads on forces in the anterior and posterior cruciate ligaments

Background: Muscle contraction can subject healing knee ligament grafts to high loads.

Purpose: To directly measure the effects of quadriceps and hamstrings muscle loads on forces in the anterior cruciate ligaments and posterior cruciate ligaments.

Study design: Controlled laboratory study.

Methods: Thirteen cadaveric knee specimens had load cells installed to record resultant forces in both anterior and posterior cruciate ligaments under 5 loading conditions. Cruciate force measurements were repeated with a 100-N load applied to the quadriceps tendon and again with a combined 50-N biceps load and 50-N semimembranosus-semitendinosus load.

Results: Applied quadriceps loads resulted in mean changes in anterior cruciate ligament and posterior cruciate ligament forces that were less than 20 N for all loading conditions. Hamstrings load significantly increased mean posterior cruciate ligament force between 30 degrees and 105 degrees of flexion with 100 N of applied posterior tibial force.

Conclusions: At the muscle force levels used in this study, the hamstrings were more effective than the quadriceps in altering cruciate force levels, especially near 90 degrees of flexion, where they have an excellent mechanical advantage for controlling anterior-posterior tibial translation.

Clinical relevance: Isolated hamstrings activity generally had little or no effect on anterior cruciate ligament forces but significantly increased forces in the posterior cruciate ligament beyond approximately 30 degrees of flexion.