The palmaris longus is a slender, inconstant forearm muscle absent in roughly 14 percent of people with no functional consequence. When present its tendon is the most superficial structure at the volar wrist crease and is identified by opposing the thumb and little finger while flexing the wrist. It is the most commonly harvested expendable tendon in reconstructive surgery, used for ACL reconstruction, flexor tendon repair, and facial reanimation procedures.
| Origin | Medial epicondyle via the common flexor tendon |
|---|---|
| Insertion | Palmar aponeurosis and flexor retinaculum |
| Nerve Supply | Median nerve (C7, C8) |
| Blood Supply | Ulnar artery |
| Actions | Tenses the palmar aponeurosis; Weak wrist flexion |
|---|
Its primary role is tensing the palmar aponeurosis during grip rather than moving the wrist, protecting the neurovascular structures of the palm from compressive forces during handling activities.
Checking for palmaris longus presence is a routine pre-operative step before any tendon graft procedure because its absence requires choosing an alternative donor site. When present, reversed palmaris longus syndrome occasionally causes carpal tunnel symptoms from a reversed tendon belly pressing on the carpal tunnel contents. Dupuytren disease involves thickening of the palmar aponeurosis into which the palmaris longus inserts.
When present, it is the central and most prominent wrist tendon visible during the Schaeffer test of opposing thumb and little finger while flexing the wrist, easily distinguished from the flanking FCR tendon laterally and the FCU tendon medially.
Rare inflammation producing central volar wrist pain reproduced by resisted wrist flexion, diagnosed only after excluding carpal tunnel, FCR, and FCU pathology as more common causes.
