The oblique head provides the primary adduction force for key pinch. Its more proximal origin gives it a greater moment arm than the transverse head.
| Origin | Capitate, bases of second and third metacarpals, palmar carpal ligaments |
|---|---|
| Insertion | Ulnar base of thumb proximal phalanx via a sesamoid bone |
| Nerve Supply | Deep branch of ulnar nerve (C8, T1) |
| Blood Supply | Princeps pollicis artery branch |
| Actions | Adducts the thumb — primary head for power and key pinch; The Froment sign results from oblique head paralysis |
|---|
Froment sign (thumb IP flexion during lateral pinch) results from oblique head denervation in ulnar palsy. Key pinch strength is disproportionately lost. Adductor pollicis reconstruction uses ring FDS transfer to the adductor insertion.
Palpated in the first web space deeper than the first DI during resisted thumb adduction.
Positive Froment sign from oblique adductor denervation — inability to maintain thumb IP extension during lateral pinch.
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