We diagnosed entrapment of the superficial peroneal nerve in 17 patients (19 legs) with a mean age of 41 years. In all cases, plain radiographs of the leg, nerve-conduction studies of the superficial peroneal nerve and measurement of the intramuscular pressure at rest after exercise were normal. Diagnostic tests for nerve compression during rest after exercise produced pain and clinical signs in all.

We performed decompression of the superficial peroneal tunnel in 14 patients and local fasciectomy in three. Fourteen patients (80%) were free from symptoms or satisfied with the result.

Entrapment of the superficial peroneal nerve was treated in 24 legs of 21 patients by fasciotomy and neurolysis; 19 of the patients were reviewed after a mean period of 37 months. Nine were satisfied with the result, another six were improved but not satisfied because of residual limitation of athletic activity, three were unchanged and one was worse. Conduction velocity in the superficial peroneal nerve had increased after operation, but the change was not significant. In five patients the nerve had an anomalous course and in 11 there were fascial defects over the lateral compartment. Chronic lateral compartment syndrome is an unusual cause of nerve entrapment. Operative decompression produces cure or improvement in three-quarters of the cases, but is less effective in athletes.

In nine patients with chronic compartment syndrome, the intramuscular pressure and muscle blood flow during constant dynamic exercise was studied by the microcapillary infusion method and by the 133-xenon clearance technique. Although muscle blood flow was normal at the start of exercise, pain and impaired muscle function eventually developed; muscle blood flow decreased while muscle relaxation pressure increased. The changes of muscle blood flow could not be correlated with any change of mean muscle pressure during exercise. Eight months after fasciotomy the exercise test was repeated. Patients experienced no symptoms and the muscle relaxation pressure and blood flow during exercise were normal. It is suggested that chronic compartment syndrome is due to increased muscle relaxation pressure during exercise which causes decreased muscle blood flow, leading to ischaemic pain and impaired muscle function.