The third lumbrical controls the fourth toe MTP joint and extensor mechanism. It is bipennate and laterally placed, working with the third plantar interosseous to stabilise the fourth ray. Loss of the third lumbrical contributes to fourth toe claw deformity in intrinsic minus conditions.
| Origin | Adjacent borders of the second and third FDL tendon slips (bipennate) |
|---|---|
| Insertion | Medial base of the proximal phalanx of the fourth toe and extensor hood |
| Nerve Supply | Lateral plantar nerve (deep branch, S2, S3) |
| Blood Supply | Third plantar metatarsal artery |
| Actions |
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It flexes the MTP joint and extends the interphalangeal joints of the fourth toe, helping keep the toe flat during push-off.
The third lumbrical is included in comprehensive EMG studies of the foot intrinsic muscles for peripheral neuropathy staging. Its selective assessment helps localise lateral plantar nerve deep branch lesions within the foot. Claw deformity at the fourth toe with intact second and third toe intrinsic function suggests a selective injury distal to the first lumbrical's medial plantar branch.
Not directly palpable. Functionally assessed by fourth MTP flexion with IP extension resistance.
Claw deformity at the fourth toe from third lumbrical loss producing MTP hyperextension and IP flexion, managed with tendon transfer or arthrodesis depending on flexibility.
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