The foot interossei (four dorsal and three plantar) are the intrinsic muscles that stabilise the toe MTP joints and control toe spread. Their atrophy in peripheral neuropathy produces the characteristic forefoot deformity of diabetes — metatarsal head prominence, MTP extension, and IP flexion (clawtoes).
| Origin | Adjacent metatarsal shafts — four dorsal (abductors) and three plantar (adductors) |
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| Insertion | Bases of the proximal phalanges and extensor expansions of toes 2-4 (dorsal) and toes 3-5 (plantar) |
| Nerve Supply | Lateral plantar nerve — deep branch (S2, S3) |
| Blood Supply | Plantar metatarsal arteries and dorsal metatarsal arteries |
| Actions | Dorsal interossei abduct the toes from the second toe axis (DAB); Plantar interossei adduct the toes toward the second toe axis (PAD); Flex the MTP joints and extend the IP joints via the extensor expansion |
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Interosseous muscle atrophy is the earliest sign of peripheral neuropathy in the foot, detectable by EMG and nerve conduction studies before clinical symptoms develop. In diabetic Charcot foot, interosseous atrophy and the resulting MTP extension places abnormal plantar pressure on the metatarsal heads, leading to neuropathic ulceration. Intrinsic foot muscle training is part of foot core strengthening programmes.
Assessed by toe spread capability and toe abduction-adduction strength against resistance.
Loss of foot interosseous muscles in diabetic neuropathy producing clawtoe deformity with metatarsal head plantar pressure and risk of neuropathic ulceration.
