Quantitative evaluation of the Myotatic Reflex in Hemiplegic and Paraplegic patients

The aim of this study was the quantitative evaluation of the myotatic reflex in a group of 11 subjects affected by spastic paresis of the lower limbs (8 hemiplegic and 3 paraplegic patients) and, for comparison, in a group of 7 healthy subjects. The parameters taken into account were the gain of the reflex and the time delay between the input and the mechanical output. The gain was calculated as the ratio between: i) the peak value of the input force (FPH) measured by means of an instrumented hammer with which the patellar tendon was hit; and ii) the peak value of the corresponding reflex force of the quadriceps femoris (FPQ) measured by means of a load cell connected to the subject's ankle. The gain of the reflex (FPQ/FPH) was found to be 1.9 to 2.4 times larger in patients as compared to control subjects and, among the patients to be twice at low, as compared to high, levels of stimulation. Among the hemiplegic patients, significant differences were found in the time delay of the response between the affected and unaffected limbs. Since both the intensity of the reflex and its gain were found to depend on the mechanical energy input, both parameters must be taken in to account if a diagnosis of spasticity has to be made.