Which nerve impairment could lead to an inability to evert the foot?

Inability to evert the foot is primarily associated with impairment of the common peroneal nerve. This nerve is responsible for the function of muscles that facilitate foot eversion, including the peroneus longus and peroneus brevis. When the common peroneal nerve is compromised, it can result in weakness or paralysis of these muscles, leading to the inability to evert the foot.

The deep peroneal nerve innervates muscles primarily involved in dorsiflexion of the foot and does not significantly contribute to eversion. The tibial nerve primarily controls the muscles that point the toes downward (plantarflexion) and does not play a role in foot eversion. The superficial peroneal nerve does contribute to eversion as it innervates the peroneus longus and peroneus brevis; however, involvement of the common peroneal nerve affects both the superficial peroneal and deep peroneal branches, which takes precedence in understanding complete foot evertor loss. Therefore, it is the common peroneal nerve impairment that leads to the direct clinical symptom of an inability to evert the foot.