Patients with lower back pain secondary to nerve root irritation especially of the S1 nerve root can have pain on turning the foot and ankle outward away from the midline of the body (foot eversion). Foot eversion is always accompanied by plantarflexion also of the foot.
Tightness due to spasm in the muscles that perform foot eversion leads to pain during this movement. You can feel the tendons of the peroneus longus and brevis as they travel behind the lateral malleolus (this bone is easily felt at the outer aspect of the ankle).
Muscles which perform foot eversion are:
- peroneus longus (L5, S1 through the superficial peroneal nerve)
- peroneus brevis (L5, S1 through the superficial peroneal nerve)
- peroneus tertius (L5, S1 through the deep peroneal nerve)