Long Head of Triceps Proximal Tendon

tendo proximalis capitis longi musculi tricipitis brachii

The long head of triceps arises from the infraglenoid tubercle of the glenoid rim via a flat tendinous origin that passes through the quadrilateral space (bounded by teres minor, teres major, humerus, and long head of triceps) alongside the posterior circumflex humeral artery and the axillary nerve. It descends to join the lateral and medial heads in the common triceps tendon inserting on the olecranon.

Region: Shoulder

Clinical Relevance

Clinical Notes

The long head of triceps proximal tendon and the quadrilateral space are relevant in two clinical settings: posterior labrocapsular periosteal sleeve avulsion (POLPSA lesion) where the posterior labrum and capsule are avulsed with posterior shoulder instability, and quadrilateral space syndrome where the axillary nerve and PCHA are compressed within the space. The tendon anchors the medial border of the quadrilateral space. Long head triceps avulsion from the infraglenoid tubercle is rare but produces posterior shoulder weakness and loss of full elbow extension strength in the elevated arm position.

Pathology

Common Injuries & Conditions

Long Head Triceps Defining the Quadrilateral Space

The long head of triceps forms the medial boundary of the quadrilateral space through which the axillary nerve and posterior circumflex humeral artery pass to reach the deltoid; quadrilateral space syndrome from fibrous bands compressing these structures produces deltoid pain and wasting reproduced by shoulder abduction and external rotation.