📝 STANDARD DESCRIPTION:
Type: Intrinsic, Antebrachial (Craniolateral/Extensor Group)
Origin: Lateral supracondylar crest of humerus
Insertion: Metacarpal tuberosity on proximal dorsal aspect of Mc III/IV
Function: Extends the carpus; assists in elbow flexion via reciprocal apparatus.
📚 DETAILED DESCRIPTION:
THE CARPAL EXTENSOR PILLAR
The most cranial and largest extensor muscle of the forearm, critical for maintaining the carpus in extension during weight bearing and the swing phase.
TOPOGRAPHIC POSITION: Lies directly beneath the skin on the craniolateral aspect of the forearm, immediately lateral to the radius. Its tendon is palpable and visible over the dorsal carpus.
STAY APPARATUS CONNECTION: Receives the lacertus fibrosus from the biceps brachii tendon. This fibrous connection allows passive transfer of tension from shoulder to carpus, assisting in keeping the carpus extended without muscular effort during standing—a key component of the bovine stay apparatus.
BIPENNATE STRUCTURE: Highly organized fascicles allow for sustained tonic contraction suitable for weight bearing rather than just rapid movement.
INSERTION: The stout tendon inserts on the large metacarpal tuberosity of the fused third and fourth metacarpal (cannon bone), providing direct extension of the carpo-metacarpal joint.
// COMPARATIVE ANALYSIS
| DOG |
Divided into longus and brevis; ox has single belly. |
| HORSE |
Similar single belly; lacertus fibrosus connection is massive and primary stay mechanism. |
CLINICAL RELEVANCE
Radial Nerve Paralysis: Low lesions spare triceps but paralyze ECR, causing the carpus to knuckle during weight bearing. Tenosynovitis: Tendon may swell within synovial sheath at carpus.
