midarm

Midarm refers to the middle segment of the upper limb, between the shoulder and the elbow. In anatomical terms it roughly corresponds to the middle third of the brachium and lies between the glenohumeral joint proximally and the elbow distally. The region is enclosed by the brachial fascia and is divided into anterior (flexor) and posterior (extensor) compartments by intermuscular septa.

Contents and landmarks

The anterior compartment houses muscles such as the biceps brachii, brachialis, and coracobrachialis, which act mainly to flex the elbow and, in the case of the biceps, assist shoulder actions. The posterior compartment contains the triceps brachii (long, lateral, and medial heads), which extend the elbow. The anconeus is nearby near the elbow. The major neurovascular structures include the brachial artery with accompanying veins, and the profunda brachii artery with the radial nerve running in the posterior aspect. The musculocutaneous nerve travels through the anterior compartment to provide motor innervation to the flexors, while the median nerve also courses with the vessels in the arm. The radial nerve innervates the posterior compartment. The ulnar nerve runs medially toward the elbow but gives no branches within the main arm compartments.

Clinical relevance

The midarm is a common site for anthropometric measurement, such as the mid-upper arm circumference (MUAC), used to assess nutritional status in adults and children. Traumatic injury to the midarm, such as a humeral shaft fracture, can involve the radial nerve and other neurovascular structures, leading to motor and sensory deficits in the distal arm and hand.