The third plantar interosseous is the most lateral of the three plantar interossei, adducting the little toe and flexing its MTP joint. Together with the ADM, it controls little toe position.
| Origin | Medial aspect of the fifth metatarsal shaft |
|---|---|
| Insertion | Medial base of the fifth toe proximal phalanx |
| Nerve Supply | Lateral plantar nerve (S2, S3) |
| Blood Supply | Plantar arch |
| Actions | Adducts the fifth toe toward the third; Flexes the fifth MTP joint |
|---|
Third plantar interosseous weakness contributes to little toe abduction deformity (varus fifth toe). In combined intrinsic minus foot, all three plantar interossei fail, producing forefoot splay.
Not individually palpable. Assessed by resisted little toe adduction.
Third plantar interosseous atrophy from neuropathy producing little toe abduction with reduced forefoot stability.
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