The Surgical Treatment of Entrapment Neuropathies of the Lower Extremity

A peripheral nerve may be damaged at any point along its course. When direct trauma is the cause there are few surprises, but on occasion nerve dysfunction occurs spontaneously without clear evidence of ex-ternal trauma. In these situations the clinician searches for other explanations and the surgeon looks for an anatomic cause to treat. In the absence of trauma, entrapment neuropathy is often considered in the differential diagnosis. As usually understood, entrapment neuropathy is an external constrictive process that, by the application of focal pressure, is responsible for the resultant dysfunction of a given peripheral nerve. Unfortunately, this understanding—although conceptually useful for the most common focal neuropathy, carpal tunnel syn-drome—is too limited mechanistically and geometrically to lend itself correctly to other focal mechanical neuropathies. Unfortunately, the term entrapment seems too well ingrained in medical parlance to be displaced at this time. Focal neuropathies amenable to surgical solutions would seem to offer a better list and are not limited to a particular geometry involving connective tissue. This article focuses on surgical solutions to those specific and characteristic locations in the lower extremity where anatomy and its variations intersect outside the physiologic boundaries of nerve function and allow focal nerve damage to occur and become clinically evident. It may be stated axomatically that the nerves of the peripheral nervous system are, in general, well protected from external forces. The ability of nerve to stretch somewhat without structural damage has been recognized for many years, 1,2 as has its ability to with-stand some pressure. 3 Along with this recognition has come the awareness that asymmetrically applied forces and pressure gradients may set in motion a series of structural and physiologic changes that will cause the nerve and its fibers to fail in function. Some of theses changes have macroscopic manifestations, such as focal