Patients with lower back pain due to irritation of the S1 and S2 nerve roots can present first with pain in the ankle, foot and toes.
Muscles that perform cupping of the sole of the foot are supplied by the S1 and S2 nerve roots. When these muscles are in pain and spasm, the foot can go into a cramp with the toes hyperflexed making the foot go into a cupping movement. Also, the short muscles of the foot may go into spasm with the toes spread wide apart.
The intrinsic muscles of the foot supplied by the medial plantar nerve, S1, S2 that perform cupping are:
- Flexor digitorum brevis. This muscle will flex the metatarsophalangeal and proximal interphalangeal joints.
- Abductor hallucis spreads the big toe away from the second digit.
The intrinsic muscles of the foot supplied by the lateral plantar nerve, S1, S2 that perform cupping are:
- Flexor digiti quinti brevis which flexes the toes at the metatarsophalangeal joint and interphalangeal joints
- Abductor digiti quinti spreads the little toe away from the fourth digit.
- Adductor hallucis which brings the big toe toward the second digit.
The intrinsic muscles of the foot supplied by the medial and lateral plantar nerves S1, S2 that assist in performing cupping are:
- Lumbricals and interossei. These muscles will flex the metatarsophalangeal joints and extend at the interphalangeal joints.