Muscle Contributions To Knee Joint Stability: Effects Of ACL Injury And Knee Brace Use

Muscle Contributions To Knee Joint Stability: Effects Of ACL Injury And Knee Brace Use
May 2007
Derouin, Aaron J.1; Potvin, James R.2
Medicine & Science in Sports & Exercise
Lippincott Williams & Wilkins

1 University of Windsor, Windsor, ON, Canada

2McMaster University, Hamilton, ON, Canada.

Anterior cruciate ligament (ACL) injury typically results in knee joint instability and loss of function. Functional knee braces have been prescribed as an adjunct treatment, along with surgical reconstruction and physical therapy, in an attempt to restore the stability provided by the previously intact ACL. Several studies have shown that braces may alter both the recruitment levels and patterns of the key stabilizing muscles acting at the knee. However, none of these studies have quantitatively determined the individual muscle contributions to mechanical knee stiffness in response to ACL injury and/or brace use.

PURPOSE: To develop an EMG-based biomechanical model of the lower extremity to evaluate the muscle rotational joint stiffness of ACL-deficient (n=9) and reconstructed (n=8) knees, with and without use of a functional knee brace.

METHODS: Kinematic, force plate, and electromyographic data were measured while subjects performed stable and unstable quasi-static squats. These data were input into a detailed linked segment biomechanical of the lower extremity. Individual and total muscle contributions to knee joint rotational stiffness were calculated about the flexion-extension axis. There were four independent variables: Squat task (stable vs.unstable); Leg condition (uninjured, unbraced, braced); Knee angle (5-10?, 20-25?, 40-45?); Injury status (control, ACL deficient, ACL reconstructed)

RESULTS: Subjects had significantly higher (p<0.05) total knee joint stiffness values while wearing the brace compared to the uninjured control leg. Additionally, leg condition had a significant main effect on the stiffiness contributions of the vastus medialis (p<0.05) and intermedius (p<0.05), and the gastrocnemius medialis (p<0.0001). The braced leg condition had significantly higher EMG levels in these vasti muscles compared to the uninjured leg, while the gastrocnemius had significantly lower EMG in the braced leg condition compared to the uninjured leg.

CONCLUSIONS: Consideration of the entire compliment of muscles, acting at the knee, is critical in the determination of knee joint rotational stiffness. The increase in knee joint rotational stiffness facilitated by the brace may act in conjunction with the passive stabilizing capacity of the brace to minimize the risk of buckling.

Š2007The American College of Sports Medicine