The second lumbrical is bipennate, arising from adjacent FDL tendon slips. It is innervated by the lateral plantar nerve, unlike the first lumbrical. It stabilises the third MTP joint and maintains the intrinsic-plus position of the third toe during the propulsive phase of gait.
| Origin | Adjacent borders of the first and second FDL tendon slips (bipennate) |
|---|---|
| Insertion | Medial base of the proximal phalanx of the third toe and extensor hood |
| Nerve Supply | Lateral plantar nerve (deep branch, S2, S3) |
| Blood Supply | Second plantar metatarsal artery |
| Actions |
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It flexes the MTP joint and extends the interphalangeal joints of the third toe, helping prevent clawing during push-off.
The lateral plantar nerve innervation of the second through fourth lumbricals means that complete lateral plantar nerve injury produces claw toes at the third through fifth toes with relative preservation of the second toe (first lumbrical medial plantar territory). This pattern helps distinguish complete plantar nerve injury from intrinsic muscle disease.
Not directly palpable. Assessed by third MTP flexion with IP extension resistance testing.
Claw deformity at the third toe from second lumbrical denervation in lateral plantar nerve injury, with preservation of second toe intrinsic function from intact medial plantar supply.
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