📝 STANDARD DESCRIPTION:
Type: Intrinsic, Forearm (Extensor Group by nerve, Flexor by action)
Origin: Lateral epicondyle of humerus
Insertion: Accessory carpal bone and proximal vestigial fifth metacarpal (Mc V)
Function: Flexes carpus (despite radial innervation); abducts limb minimally.
📚 DETAILED DESCRIPTION:
THE CARPAL FLEXOR PARADOX
Morphologically classified as an extensor (supplied by radial nerve) but positioned caudal to the axis of rotation, making it functionally a carpal flexor.
ACCESS CARPAL ANCHOR: Inserts on the prominent accessory carpal bone, the pulley-like bone on the caudolateral carpus. This insertion provides mechanical advantage for flexion and lateral stability.
VESTIGIAL DIGIT CONNECTION: Also inserts on the vestigial fifth metacarpal (dewclaw bone), representing the structural remnant of digit V.
LATERAL STABILITY: Provides lateral support to the carpus during weight bearing, preventing excessive medial deviation of the carpus.
NEURAL BLOCK LANDMARK: The groove between Ulnaris Lateralis and Flexor Carpi Ulnaris is the critical landmark for performing the Ulnar Nerve Block at the distal forearm level.
// COMPARATIVE ANALYSIS
| HORSE |
Similar paradoxical flexor function; same landmark usage. |
| DOG |
Separate tendon slips to digit V when present. |
CLINICAL RELEVANCE
Ulnar Nerve Block Site: Palpable groove ~10cm proximal to accessory carpal bone between this muscle and FCU is THE landmark for ulnar block. Carpal Flexion Weakness: Rarely injured alone but contributes to carpal drop in severe flexor deficits.
