An electrophysiological method for examining lumbosacral root compression.

The propagation velocities and conduction times of nerve impulses responsible for muscle F-waves were measured in the proximal segments of 60 normal posterior tibial nerves and of 41 normal peroneal nerves. The results were compared with those of 25 patients having confirmed lumbosacral root compression due to disc degeneration. Using the peroneal nerve, 65 per cent of patients had a prolonged proximal conduction time; a similar abnormality was found in 56 per cent of patients when the posterior tibial nerve was studied. The yield of positive results rose to 85 per cent and 76 per cent respectively when the M- and F-latencies in given individuals were compared. It was also shown that in normal subjects the F-response has a longer latency, and slower conduction velocity than the H-reflex when both are obtained using the same stimulating and recording sites. In patients in whom the ankle jerks and H-reflexes are absent, the F-waves may still be recorded indicating that the latter are mediated through motor fibers.