Abstract
It is important for clinical EMG to ensure a quantitative description of the behavior of the motor unit. The measurement of the duration of the motor unit is particularly useful in discovering the degree of muscle damage.
The purpose of this paper is to find out quantitatively the degree of the damage of muscles in pre-operative and post-operative stages in patients with intervertebral disc herniations (IDH) by means of the computer-assisted analysis of the duration of motor unit. The cases studied consisted of 34 subjects with IDH and, 20 normal subjects as controls. The muscles examined were the extensor hallucis longus (EHL) the tibialis anterior (TA) and the gastrocnemius (GC). The durations of 300 motor units which discharged consecutively during weak voluntary contractoin were displayed in the form of a histogram. The results obtained were as follows :
1) All the normal EHL, TA, and GC muscles showed a relatively steep one-peak type of duration histogram (DI-I). The peak was located at 2-4 msec, and the mean values of the endpoints were at 8.25 1.65msec for EHL, 9.35-4-1.23rnsec for TA, and 8.01 1.22msec for GC.
2) The types of DH of the patients with IDH were classified into four groups : normal, one-peak, two-peak and multiple-peak forms. The latter three forms demonstrated a wide DH indicating the presence of the motor unit of long duration.
3) The abnormal types of DH at the pre-operative stage occurred in 94.7% of the cases of EHL at the level of L4-5 One month after the operation, the percentage remained the same as before, but it became 73.3% 3 months later, 50.0% 6 months later, and 41.2% 12 months later, showing a gradual decrease.
4) In the group of L5-S1, IDH, all the 15 cases of GC were of the abnorwal type before the operation. But the incidence was reduced to 84.6% 1-3 months later and 53.8n 6 months later.
To summarize the above findings, it can be stated that the abnormal DH tends to return into the normal DH in 3-6 months following the operation.
From these results, the author assumed that the damage to the nerve roots would cause the appearance of the motor unit of long duration such as complex NMU and grouping voltage, threreby producing the wide DH.
