Document Title: Markolf-AJSM-Jul04.shtml
Article Title: Effects of Applied Quadriceps and Hamstrings Muscle Loads on Forces in the Anterior and Posterior Cruciate Ligaments
Authors: Keith L. Markolf, PhD, Geoffery O’Neill, Steven R. Jackson, and David R. McAllister, MD.
Publication: American Journal of Sports Medicine, Baltimore, Maryland
Date: July 2004
Volume 32, pages 1144-1149
Keywords: Anterior Cruciate Ligament, ACL, Posterior Cruciate Ligament, PCL, knee biomechanics, physiology, quadriceps, hamstrings, muscle groups, musculature, flexion angle.

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Comments: This study shows how even normal muscle contraction forces can generate very high tensile forces in knee-ligament grafts. The findings show how both quadriceps and hamstring musculature affect both the ACL and the PCL.

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° and 105° 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° 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° of flexion.

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