Quadriceps femoris and hamstring muscle function in a person with an unstable knee

Background and Purpose, The pur-pose of this case report is to describe the evaluation, treatment, and short-term outcome for an individual with chron ic, progressively worsening instability of the knee during gait associated with anterior cruciate ligament (ACL) insufficiency. Case Description. The patient was a 34-year-old man who sustained bilateral ACL injuries. Subsequ ently, an autograft reconstruction of the left knee ACL aas performed. Eigh t months post-reconstruction, the left knee was unstable despite bracing. G ait analysis and tests to determine the presence of muscle inhibition were performed prior to and after 12 weeks of training. Isometric torque of the knee extensors and flexors was measured with the knee in 90 degrees of flex ion. A training program primarily consisted of electromyographic biofeedbac k during thigh muscle exercises, balance exercises, and gait. Outcomes. Mus cle inhibition decreased and maximal isometric knee flexion and extension t orques increased during the 12-week training period. Gait analysis demonstr ated a 50% decrease in the maximum knee extensor moment and an increase in walking speed. Discussion. Selected gait variables, torque production, and muscle inhibition may change in a person with an unstable knee. The measure ment of variables that have previously been documented as mechanisms of kne e instability during walking allows for the selection of a specific treatme nt approach.