Introduction

The upper extremity (UE) is comprised of its associated muscles, nerves, and vessels, organised into anatomical compartments.The muscles cross joints to provide tone, maintain dynamic joint stability, and perform dynamic functions of the entire extremity. In addition, the arteries and veins provide nourishment and remove waste, and the nerves provide the motor and sensory innervation.

Structure and Function

The muscles of the shoulder originate from both the axial skeleton and the scapula, inserting onto the humerus. The muscles that originate from the anterior compartment of the brachium act to flex the forearm while the muscles with their origins from the posterior compartment of the brachium act to extend the forearm. Much like the brachium, the anterior muscles of the forearm act to flex the wrist joint, and the posterior muscles act to extend the wrist joint.[1] The hand is comprised of eleven separate compartments. These are the four dorsal interossei, three volar interossei, the thenar, the hypothenar, the adductor, and the mid­palm compartments, respectively.[2] The dorsal interossei act to abduct the digits, and the volar interossei act to adduct the digits. The thenar and adductor compartment muscles exert activity on the thumb, while the muscles of the hypothenar compartment act on the small finger. Embryology The embryology of the muscles in the upper extremity is a step­wise process. The first step is where myogenic progenitor cells present in somites give rise to the primary myotomes.[3] The second wave of myogenic progenitors arises from dermomyotomes that give rise embryonic myoblasts.[3] The myoblasts then proliferate, fuse and ultimately give rise to the primary muscle fibers.[3] Blood Supply and Lymphatics The anatomical components of the UE receive vascular supply via the subclavian artery and its branches. It first transitions into the axillary artery to supply the shoulder. The axillary artery then transitions into the brachial artery to supply the brachium. The brachial artery splits distally into the radial and ulnar arteries to supply the forearm and hand. The deoxygenated blood of the upper extremity drains via the cephalic, basilic, and the brachial veins, which then flow into the subclavian vein and ultimately to the heart. The extracellular fluid is cleared by the lymphatic system. The right upper extremity feeds the right lymphatic duct, and the left upper extremity empties into the thoracic duct.[1] Nerves Innervation to the upper extremity derives from the brachial plexus. It is comprised of the ventral rami from C5 to T1 nerve roots. The anterior muscles of the upper extremity receive innervation from the musculocutaneous, the median