The long head of triceps originates by a flat tendon from the infraglenoid tubercle of the scapula and descends between teres minor (above) and teres major (below). In doing so it divides the space between these muscles into the triangular space medially and the quadrangular space laterally, forming the lateral border of the first and the medial border of the second. It is the only head of triceps that crosses the shoulder joint and contributes to shoulder adduction and extension as well as elbow extension.
| Muscle | |
|---|---|
| Attachment | Infraglenoid tubercle of the scapula |
Extends the elbow and assists shoulder extension and adduction
The long head triceps proximal tendon is at risk in posterior shoulder approaches and quadrangular space dissection. Proximal long head triceps avulsion or strain at the infraglenoid tubercle is uncommon, seen in throwers and after posterior dislocation, producing posterior shoulder pain and triceps weakness with MRI signal change at the origin. Because the tendon borders the quadrangular space, which transmits the axillary nerve and posterior circumflex humeral artery, it is a key landmark in quadrangular space syndrome, where fibrous bands compress these structures and cause deltoid weakness and posterior shoulder pain in abduction and external rotation. The circumflex scapular artery passes through the neighbouring triangular space.
Rare traction injury at the infraglenoid tubercle producing posterior shoulder pain and elbow extension weakness, confirmed by MRI showing the retracted tendon stump.
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