Lumbar root innervation of the medial foot and ankle region

Background: Differences in the dermatomal maps appearing in standard anatomic texts which are in common use may lead to diagnostic confusion in the assessment of patients who suffer from nerve root deficiency. This is particularly evident in the variable depiction of the LA nerve root dermatome which is carried distally in the saphenous nerve. The purpose of this study is to establish the distal limit of L4 nerve root innervation in the foot by performing cadaveric dissection of the saphenous nerve. Methods: Dissection of the dot-sum of the medial foot and ankle was performed on 20 cadaveric specimens. Results: The saphenous nerve was found to enter the dermis of the medial ankle region (mean = 14.75 mm) distal to the tip of the medial malleolus in the direction of the hallux. In three cases the nerve terminated proximal to the medial malleolus. In all cases the medial forefoot and hallux were supplied by the most medial branch of the superficial peroneal nerve. Conclusions: These findings suggest that the sensory component of the L4 nerve root terminates in most cases near the medial malleolus, well proximal to the bunion area of the forefoot.