Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

The posterior leg is mainly supplied by which dermatome?

1. Dermatome S1

2. Dermatome S2

3. Dermatome L5

4. Dermatome S3-S5

The correct answer is: Dermatome S2

The posterior leg is primarily supplied by the dermatome S2. This area includes the skin on the back of the leg and parts of the calf. Dermatomes are areas of skin that are mainly supplied by a single spinal nerve root, and S2 contributes significantly to the sensory innervation in this region, particularly for sensations like touch and pain. Dermatome S1 also plays a role in the lower limb's sensory innervation, but it is more associated with the lateral aspect of the foot and part of the posterior leg. Dermatome L5 is mainly responsible for the dorsum of the foot and the lateral side of the leg. The S3-S5 dermatome group primarily supplies the perineal area and is not involved in the direct innervation of the posterior leg. Thus, the dermatome S2 is recognized for its predominant sensory contribution to the posterior aspect of the leg.