Quantitation of axon loss and conduction block in peroneal nerve palsies.

We compared conduction in motor fibers supplying the extensor digitorum brevis (EDB) and anterior lateral compartment (AL) muscles. The object was to determine whether there were any differences in the relative proportions of degenerated and blocked nerve fibers between the longer EDB and shorter AL fibers. In almost every case the percentage of motor fibers undergoing axonal degeneration was greatest in EDB fibers. Conversely, the percentage of conduction block was greatest in the AL motor fibers. As clinical recovery is dependent on AL muscles rather than EDB, electrophysiological study of the relative proportions of degenerated and blocked fibers in the former should provide a more reliable measure of outcome than similar studies of EDB. Conduction velocity distal to the fibular head was not slowed despite the large loss of EDB motor fibers. Evidence for selective involvement of the larger myelinated fibers is, therefore, lacking. The location of the major conduction abnormalities was in almost every case between the mid-fibular head and popliteal fossa.