Anatomy and Histological Reaction of Traumatized Nerves

Abstract

A special comparable system of nerve trunks passes through the upper and lower limbs, which must be thoroughly understood by every physician treating peripheral nerve lesions. It is astonishing that the ramifications of nerves and the special muscles innervated by these nerves are totally comparable between the upper and lower limbs (► Fig. 2.1). Imagining this comparability facilitates the clinical investigation of patients suffering from incomplete or complete nerve lesions. Anatomically and functionally comparable are the axillary (circumflex) nerve and obturator nerve, the musculocutaneous nerve and femoral nerve, the median nerve and medial plantar nerve, the ulnar nerve and lateral plantar nerve, the radial nerve and common peroneal nerve, as are the individual ramifications of the radial and common peroneal nerves, that is, their superficial branch as well as their deep branch (posterior interosseous nerve in the lower arm). Important ramifications may vary depending on their possible levels; these variations must be taken into account in nerve surgery, but most of them are not of great importance, for example, the ramification of the sciatic nerve into the tibial and peroneal nerves as well as the ramification of the tibial nerve into the medial and lateral plantar nerves. However, there are three ramifications of the upper limb nerves that cannot be mentioned often enough, which will raise serious problems in the assessment of certain lesions during surgery. For example, motor fibers innervating the thenar muscles, which are normally found within the median nerve, may remain located within the ulnar nerve (RicheCannieu anastomosis), a fairly frequent situation in humans. These motor fibers leading to the thenar muscles may arise from the ulnar nerve fibers at different unknown levels and then join the median nerve fibers. In some cases, the motor branch of the thenar muscles even leaves the ulnar nerve at the palm level. In such cases, actually not all that rare, a complete loss of continuity of the median nerve trunk would not result in thenar muscle paresis, and a surgically reconstructed median nerve could not restore any real thenar function.