Dynamics of patellar tendon reflex in spastic multiple sclerosis patients

Patellar tendon reflexes were studied in fourteen normal subjects and ten multiple sclerosis (MS) patients. An instrumented hammer was used to tap the patellar tendon and record the tapping force, while the quadriceps EMG and knee extension torque were recorded isometrically as the reflex responses. The relationship between tapping force and reflex torque was characterized using several system measures: the tendon reflex gain (G/sub tr/), contraction rate (R/sub c/), half-relaxation rate (R/sub hr/), contraction time (t/sub c/), half-relaxation time (t/sub hr/), and reflex loop delay (t/sub d/). G/sub tr/, R/sub c/, and R/sub hr/ of the MS patients were significantly higher than their counterparts in normal controls (p<0.001 for all cases). t/sub d/ of the MS patients was significantly shorter than that of the normal group (p<0.005). G/sub tr/, R/sub c/, and R/sub hr/ values correlated more closely with clinical measures of spasticity (Ashworth scale and tendon reflex scale) than did pure output measures (peak reflex torque and quadriceps EMG signals). Tendon reflexes were more repeatable in the MS population than in normal controls. The higher correlation to clinical measures and lower variation of G/sub tr/, R/sub c/, and R/sub hr/ indicate the potential values of these dynamic system measures in clinical practice as a more accurate and consistent approach towards quantification of the tendon jerk and spasticity.