Topic Overview

 Arm

Introduction

• The arm (also called brachium) is the part of the upper limb between the shoulder joint and the elbow joint.

• It is divided into anterior (flexor) and posterior (extensor) compartments by medial and lateral intermuscular septa extending from the deep fascia to the humerus.

• Each compartment contains muscles, nerves, and vessels with distinct functions.

• The anterior compartment mainly performs flexion at the elbow and is supplied by the musculocutaneous nerve.

• The posterior compartment mainly performs extension at the elbow and is supplied by the radial nerve.

• The main artery of the arm is the brachial artery, and the main superficial veins are the cephalic, basilic, and median cubital veins.

Surface Landmarks of the Arm

Anterior Aspect

• Deltoid muscle → forms rounded contour of shoulder.

• Biceps brachii → visible when flexed; its tendon palpable in front of elbow.

• Bicipital groove (between biceps and triceps) → indicates position of brachial artery and median nerve.

• Medial epicondyle of humerus → easily palpable; ulnar nerve lies behind it.

• Lateral epicondyle → gives origin to common extensor muscles.

Posterior Aspect

• Triceps muscle → forms the bulk of posterior arm.

• Olecranon process of ulna → prominent at back of elbow.

• Posterior groove of arm → corresponds to course of radial nerve and profunda brachii artery (radial/spiral groove).

Bony Landmarks (Palpable Points)

• Acromion process of scapula – lateral end of shoulder.

• Greater and lesser tubercles of humerus – felt with rotation of arm.

• Medial and lateral epicondyles – at distal humerus.

• Head of radius – palpable on lateral aspect just below lateral epicondyle (moves during supination/pronation).

• Olecranon process – posterior tip of elbow.

Lines & Triangles

• Three bony points – medial epicondyle, lateral epicondyle, and olecranon process – are in a straight line when the elbow is extended and form a triangle when flexed.

• This relationship is clinically important to detect supracondylar or dislocation injuries