Abstract

Reflex response times of the vastus medialis obliquus and vastus lateralis were evaluated in 41 normal subjects and 16 patients with extensor mechanism dysfunction. The reflex response times for both muscles to a patellar tendon tap were evaluated by electromyography. The latencies of the muscles were statistically analyzed in both groups. In normal subjects, one-tailed paired-sample t-tests determined that the vastus medialis obliquus fired significantly faster than the vastus lateralis (P less than 0.001). In the patients, the vastus lateralis fired significantly faster than the vastus medialis obliquus (P less than 0.001). A chi square goodness of fit test demonstrated a dependency between the order of muscle firing and the type of subject (P less than 0.001). Two-tailed independent-sample t-tests revealed that the patients demonstrated a significantly faster vastus lateralis response time than the normal subjects (P less than 0.001), whereas the vastus medialis obliquus times were not significantly different. This increase in vastus lateralis reflex response time may indicate a motor control problem in the patient with extensor mechanism dysfunction. Results indicate that there is a reversal of the normal muscular firing order between the two muscles in these patients. Patients with extensor mechanism dysfunction may be demonstrating a neurophysiologic motor control imbalance that may account for or contribute to their anterior knee pain.