Correct Answer: A. Infraglenoid tubercle of scapula
Hyperextension of the shoulder during gym training creates a forceful posterior and downward pull on the arm, which places maximal tensile stress on the triceps brachii muscle. The triceps originates from three heads: the long head arises from the infraglenoid tubercle of the scapula, while the lateral and medial heads originate from the posterior humerus. During hyperextension, the long head of triceps is maximally stretched and bears the greatest load. The infraglenoid tubercle, being the bony attachment point of this long head, becomes the site of avulsion injury. This is a classic mechanism in young athletes performing overhead or eccentric loading exercises (common in Indian gym culture and sports training). The infraglenoid tubercle is a small, roughened prominence located on the inferior aspect of the glenoid cavity, making it biomechanically vulnerable to avulsion when the triceps is forcefully stretched. Avulsion fractures at this site are well-documented in young, active individuals and represent a significant cause of posterior shoulder pain in the athletic population.
Why the other options are wrong
B. Deltoid tubercle of humerus — The deltoid tubercle is the insertion point of the deltoid muscle on the lateral shaft of the humerus, not the triceps. Hyperextension primarily stresses the triceps (extensor), not the deltoid (abductor/flexor). Deltoid avulsion occurs with direct trauma or anterior shoulder dislocation, not hyperextension. This is an NBE trap using a nearby anatomical landmark to confuse students unfamiliar with muscle attachments. C. Supraglenoid tubercle of scapula — The supraglenoid tubercle is the origin of the long head of biceps, not triceps. Biceps is an elbow flexor and shoulder flexor; hyperextension would relax (not stress) the biceps. Biceps avulsion occurs with forced elbow extension or heavy lifting in flexion, not shoulder hyperextension. This option exploits confusion between the two glenoid tubercles. D. Shaft of humerus — The humeral shaft is the diaphysis and is not a specific muscle attachment site vulnerable to avulsion. Hyperextension causes tensile stress at muscle origins/insertions (bony prominences), not along the shaft itself. Shaft fractures occur from direct trauma or pathological bone disease, not from muscular traction. This is a distractor option for students who don't understand avulsion injury mechanics.
High-Yield Facts
- Infraglenoid tubercle is the origin of the long head of triceps brachii—the only triceps head originating from the scapula.
- Hyperextension of shoulder creates maximal tensile stress on the triceps long head, predisposing to avulsion fracture at the infraglenoid tubercle.
- Avulsion fractures at the infraglenoid tubercle are common in young athletes (15–25 years) performing overhead or eccentric loading exercises.
- Infraglenoid tubercle is located on the inferior aspect of the glenoid cavity, making it biomechanically vulnerable to traction injuries.
- Triceps avulsion presents with posterior shoulder pain, weakness in elbow extension, and loss of arm power—critical in gym-goers and overhead athletes.
Mnemonics
SUPRA vs INFRA Glenoid Tubercles SUPRA = Supraglenoid = Short head of Biceps (actually long head, but mnemonic: Superior = Start of biceps). INFRA = Infraglenoid = Is for triceps (long head). Use: When asked about glenoid tubercle attachments in shoulder injuries. Triceps Origins (3 Heads) Long head = Infraglenoid tubercle (scapula) | Lateral head = Posterior humerus (upper) | Medial head = Posterior humerus (lower). Hyperextension stresses the long head → infraglenoid avulsion. Use: To recall which triceps head is at risk in hyperextension injuries.
NBE Trap
NBE pairs the two glenoid tubercles (supraglenoid and infraglenoid) as options to trap students who confuse the origins of biceps and triceps. Students unfamiliar with the triceps anatomy may default to the supraglenoid tubercle (biceps origin) without considering the biomechanics of hyperextension.
Clinical Pearl
In Indian gym culture and sports training, triceps avulsion at the infraglenoid tubercle is an underdiagnosed cause of posterior shoulder pain in young athletes. Imaging (X-ray or CT) may show a small avulsion fragment; MRI reveals soft-tissue edema. Early recognition prevents chronic weakness and functional disability in overhead athletes.
_Reference: Bailey & Love Ch. 35 (Shoulder and Arm Anatomy); Robbins Ch. 27 (Musculoskeletal Injuries)_