📝 STANDARD DESCRIPTION:
Lateral Shoulder Controller
- Origin: C6, C7
- Path: Dives into quadrangular space (between subscapularis and teres major) to reach lateral shoulder
- Motor: Deltoid, Teres Major, Teres Minor (shoulder flexors)
- Sensory: Cranial Lateral Cutaneous Brachial Nerve → lateral shoulder skin
Clinical: Atrophy of deltoid, small patch of anesthesia over lateral shoulder. Less debilitating than suprascapular injury.
📚 DETAILED DESCRIPTION:
THE LATERAL SHOULDER CONTROLLER
The Axillary nerve supplies the 'meat' muscles of the lateral shoulder—the flexors and rotators that fine-tune shoulder position during the stride.
ORIGIN & PATHWAY:
Arises from C6-C7 roots. Takes characteristic deep course through the quadrangular space—an anatomical interval bounded by:
• Cranial: Subscapularis
• Caudal: Teres Major
• Lateral: Humeral shaft
Emerges into lateral shoulder region to innervate the deltoid complex.
MOTOR SUPPLY:
• Deltoid (Deltoideus): Shoulder flexion and abduction
• Teres Major: Shoulder extension and adduction (assists latissimus dorsi)
• Teres Minor: Lateral stabilization and rotation
Functional Role: These muscles provide the 'shock absorption' and positioning control for the shoulder joint during impact phase of stride.
SENSORY DISTRIBUTION:
Continues as the Cranial Lateral Cutaneous Brachial Nerve:
• Emerges at cranial border of deltoid or through muscle belly
• Supplies skin over point of the shoulder and lateral brachium
• Overlaps with radial nerve territory
CLINICAL PRESENTATION:
Motor Deficits: Less functionally debilitating than suprascapular nerve injury because infraspinatus (radial stabilization) remains intact.
• Subtle atrophy of deltoid—flattening of lateral shoulder contour
• Weakness in shoulder flexion and abduction
• Normal weight bearing maintained
Sensory Deficits: Small patch of anesthesia over lateral shoulder (often missed unless specifically tested).
INJURY MECHANISMS:
• Cranial dislocations of humerus: Humeral head compresses nerve against caudal border of subscapularis
• Deep shoulder wounds: Penetrating trauma to quadrangular space
• Fractures: Proximal humeral fractures involving surgical neck
// COMPARATIVE ANALYSIS
| DOG |
More susceptible to injury due to mobility of shoulder joint. Quadrangular space smaller. |
| HORSE |
Deltoid complex less developed. Similar quadrangular space anatomy. |
CLINICAL RELEVANCE
Differential Diagnosis: Isolated axillary injury rarely causes lameness visible at walk. Recognized by deltoid atrophy + intact sensation over lateral forearm (radial territory) combined with small sensory patch deficit. Prognosis: Better than suprascapular injury—often recovers with rest as shoulder position less critical for weight bearing.
