The triangular interval is an anatomical space located immediately below the axilla region. It allows structures to pass between the anterior and posterior compartments of the upper arm, as well as between the posterior compartment and the axilla. In this article, we shall look at the anatomy of the triangular interval – its borders, contents and clinical correlations. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Borders The triangular interval is orientated with the base superiorly and apex inferiorly. It has three borders: Superior – Inferior border of the teres major. Lateral – Shaft of the humerus and lateral head of the triceps brachii. Medial – Lateral border of the long head of the triceps brachii. By TeachMeSeries Ltd (2025) Fig 1Borders of the triangular interval. Contents The triangular interval is a passageway that allows structures to travel between: Anterior and posterior compartments of the upper arm Posterior compartment of the upper arm and the axilla It contains the radial nerve and profunda brachii artery (and accompanying vena comitantes), as they travel into the posterior compartment of the upper arm. Adobe Stock, Licensed to TeachMeSeries Ltd Fig 2Contents of the triangular interval Clinical Relevance Triangular Interval Syndrome Triangular interval syndrome refers to compression of the radial nerve as it passes through the triangular interval. It is thought to occur secondary to hypertrophy of triceps brachii or teres major. The nerve may also be compressed by fibrous bands spanning between these two muscles. Clinical features of triangular interval syndrome include: Neuropathic pain or paraesthesia in the sensory distribution of the radial nerve. Weakness in extension of the elbow, wrist, or digits. Do you think you’re ready? Take the quiz below Pro Feature - Quiz The Triangular Interval Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 1800 More Questions Available Upgrade to TeachMeAnatomy Pro Challenge yourself with over 1800 multiple-choice questions to reinforce learning Learn More Print Article Rate This Article