Comparative reflex response times of vastus medialis obliquus and vastus lateralis in normal subjects and subjects with extensor mechanism dysfunction

Abstract

Reflex response times of the vastus medialis obliquus and vastus lateralis were evaluated in 41 normal sub jects and 16 patients with extensor mechanism dys function. The reflex response times for both muscles to a patellar tendon tap were evaluated by electro myography. The latencies of the muscles were statis tically analyzed in both groups. In normal subjects, one- tailed paired-sample t-tests determined that the vastus medialis obliquus fired significantly faster than the vas tus lateralis (P < 0.001). In the patients, the vastus lateralis fired significantly faster than the vastus medi alis obliquus (P < 0.001). A chi square goodness of fit test demonstrated a dependency between the order of muscle firing and the type of subject (P < 0.001). Two- tailed independent-sample t-tests revealed that the pa tients demonstrated a significantly faster vastus later alis response time than the normal subjects (P < 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 prob lem in the patient with extensor mechanism dysfunc tion. 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 con tribute to their anterior knee pain.