Surgical anatomy of the superficial peroneal nerve in the ankle and foot.

The subcutaneous (sensory) portion of the superficial peroneal nerve was dissected in 25 cadaver lower limbs under loupe magnification. Three distinct branching pattern types were noted. Type A (72%) consisted of a pattern where the nerve penetrated the crural fascia to become subcutaneous at an average distance of 12.3 cm proximal to the ankle joint, then divided at a mean distance of 4.4 cm proximal to the ankle into two major branches: a large medial dorsal cutaneous nerve and a smaller more laterally located intermediate dorsal cutaneous nerve. Type B (16%) consisted of a pattern where both the medial and intermediate dorsal cutaneous nerve arose independently from the superficial peroneal nerve, with the medial dorsal cutaneous nerve having a similar course to that found in Type A, while the intermediate dorsal cutaneous nerve penetrated the crural fascia posterior to the fibula 5.5 cm proximal to the ankle joint and coursed medially to cross the lateral aspect of the fibula at mean distance 4.5 cm above the ankle joint. Type C (12%) consisted of a pattern where the medial dorsal cutaneous nerve and the intermediate dorsal cutaneous nerve arose independently and the medial dorsal cutaneous nerve coursed similar to that in Type A; however, the intermediate dorsal cutaneous nerve penetrated the crural fascia anterior to the fibula an average of 4.9 cm above the ankle joint and continued in close proximity to the anterior fibular border. In all patterns the mean diameters of the medial dorsal cutaneous nerve and intermediate dorsal cutaneous nerve at the ankle were 2.9 mm and 2 mm, respectively. At the level of the malleoli, the medial dorsal cutaneous nerve was located approximately one half the distance from the lateral malleolus to medial malleolus while the intermediate dorsal cutaneous nerve was approximately one third the distance. Appreciation of these branch patterns and the quantified relationships should assist nerve protection during surgical procedures as well as aid rapid nerve isolation for exploration or decompression. Branches especially at risk for iatrogenic injury include: (1) the intermediate dorsal cutaneous nerve of Type B where the nerve crosses the lateral surface of the distal fibula; (2) the intermediate dorsal cutaneous nerve of Type C where the nerve travels adjacent to the anterior border of the fibula; and (3) the intermediate dorsal cutaneous nerve and the medial dorsal cutaneous nerve at the level of the ankle, where they are at risk during anterior ankle arthrotomy or arthroscopy.