Which myotome is responsible for knee flexion and plantarflexion?

The myotome primarily responsible for knee flexion and plantarflexion is indeed S2. Knee flexion is mainly facilitated by muscles such as the hamstrings, which are innervated by the tibial nerve, a branch of the sciatic nerve. The roots of the sciatic nerve that contribute to this innervation originate at S1 and S2. Plantarflexion is also primarily associated with the muscles of the posterior compartment of the leg, which are likewise innervated by the tibial nerve.

At the S2 level, there is significant contribution to both the flexion at the knee joint and the movement at the ankle joint during plantarflexion, highlighting its key role in these movements. This makes S2 an essential myotome in evaluating motor function in these areas of the lower extremity.

The other myotomes listed do play roles in lower limb function, but they do not specifically encompass both knee flexion and plantarflexion as S2 does. For instance, L3 is more closely associated with knee extension, L5 is involved in dorsiflexion and toe extension, and S1 is more related to foot eversion and some aspects of plantarflexion, but not specifically knee flexion.