📝 STANDARD DESCRIPTION:
Type: Intrinsic, Scapulohumeral
Origin: Supraspinous fossa of scapula
Insertion: Greater and lesser tubercles of humerus (bridges intertubercular groove)
Function: Extends shoulder joint; prevents shoulder flexion/collapse during weight bearing (cranial collateral ligament equivalent).
📚 DETAILED DESCRIPTION:
THE ANTI-GRAVITY STABILIZER
Filling the supraspinous fossa, this muscle is the primary extensor of the shoulder and prevents the joint from collapsing into flexion during the weight-bearing phase. It effectively functions as the cranial collateral ligament of the shoulder joint.
TENDON ARCHITECTURE: The tendon divides to attach to both the greater and lesser tubercles, effectively bridging across the intertubercular (bicipital) groove. This creates a tense band preventing flexion collapse.
BIOMECHANICAL IMPERATIVE: During the stance phase, the weight of the cranial trunk creates a flexion moment at the shoulder. The supraspinatus provides the constant tonic contraction (and passive tension in the tendon) to oppose this, locking the shoulder in extension so the limb acts as a rigid column.
NEURAL SUPPLY: Suprascapular nerve (C6-C7).
SWEENEY PATHOLOGY: When the suprascapular nerve is damaged at the scapular neck, this muscle atrophies rapidly (neurogenic atrophy), leading to loss of shoulder extension capability and the characteristic 'shoulder slip' when infraspinatus also fails.
// COMPARATIVE ANALYSIS
| HORSE |
Similar function; prone to direct trauma during neck of scapula passage. |
| DOG |
Smaller relative to body size; less critical for weight bearing due to quadrupedal mechanics. |
CLINICAL RELEVANCE
Sweeny (Suprascapular Paralysis): Atrophy results in prominent scapular spine; loss of shoulder extension stability causes 'dropped' shoulder during weight bearing.
