Overview of Upper Limb

Written Learning Objectives 

1. Describe the contents and composition of muscle compartments.

Muscle compartments are groups of muscles that share similar neurovascular supply and actions enveloped in deep fascia, and separated from other compartments by comparatively thick layers of deep fascia, referred to as intermuscular septa, which also often attach to bone. Escaped blood, suppuration caused by infection, etc. can lead to increased pressure within these relatively unyielding compartments leading to compartment syndrome.

2. Describe the main muscle groups or muscle compartments of the upper limb.

The upper limb consists of four major segments. Each of these segments is divided into regions/muscle compartments for more precise description.

3. Understand details (attachments, actions, innervation, blood supply, etc.) regarding the anterior and posterior compartments of the arm and forearm, as well as the deltoid m.

Click here for a downloadable PDF version of the individual muscle charts.

Click here for a downloadable PDF of a comprehensive muscle chart. 

*Students are only responsible for muscles discussed in the main text of the learning objectives and/or list of structures


Deltoid m. 

Anterior compartment of arm


Posterior compartment of arm

Anterior (flexor/pronator) compartment of forearm

This compartment is organized into three layers, largely with superficial muscles acting upon proximal joints, and intermediate and deep levels action upon progressively more distal joints.

These muscles are mostly innervated by the median n., with some contributions from the ulnar n.

Superficial Layer Muscles:

Posterior (extensor/supinator) compartment of forearm

The posterior compartment of the forearm is conceptualized in 2 layers: superficial and deep, largely with superficial muscles acting upon proximal joints, and deep levels action upon progressively more distal joints. These muscles are innervated by the radial n. and its branches.


Superficial Layer Muscles:

4. Describe the primary arterial supply of the upper limb.

The axillary artery is the primary blood supply to the upper limb.

As a continuation of the subclavian a. beyond the inferior margin of the 1st rib, the axillary a. courses through the axilla, giving off numerous branches to supply the shoulder muscles and joint. The axillary a. continues into the arm as the brachial a. at the inferior margin of teres major m.

The brachial a. supplies the anterior (flexor) compartment of the arm. Proximally, the brachial a. gives off the deep artery of the arm (deep brachial a.), that dives posterior to the humerus to supply the posterior (extensor) compartment of the arm.

The brachial a. continues through the anterior compartment into the cubital fossa (anterior to the elbow), where it divides into the radial a. and ulnar a. Note, that at the elbow (as is the case with most joints), there are several branches from several different arteries that supply the joint area – they form numerous anastomoses that provide significant collateral supply to the joint and surrounding tissue.

The radial a. supplies the radial side (lateral) of the forearm flexors as it courses through the anterior forearm. At its distal end (at the wrist) it courses onto the dorsum of the lateral hand to run between the tendons of the extrinsic thumb muscles – often referred to as the “anatomical snuff box”. Abduct and extend your own thumb to see the tendons and notice the space between the tendons at your wrist – anatomical snuff box. The radial artery courses through this space onto the dorsum of the hand between the thumb and index finger. It dives through the muscle there to supply the deep palmar region of the hand.

The ulnar a. supplies the ulnar side (medial) of the forearm flexors as it courses through the anterior forearm. It courses across the wrist (where there is a good pulse point) into the hand to primarily supply the superficial palmar region of the hand. The ulnar and radial arteries anastomose (via deep and superficial palmar arches created by the radial and ulnar arteries) in the palmar region of the hand. Please refer to Session 20 for more detail.

At the proximal end of the ulnar artery, just distal to the cubital fossa area, the ulnar artery gives off the common interosseous a., that divides into anterior interosseous a. and posterior interosseous a. The anterior interosseous a. runs on the anterior surface of the interosseous membrane to supply the deep (flexor) compartment. The posterior interosseous a. runs on the posterior surface of the interosseous membrane to supply the posterior (extensor) compartment.

In fewer words [note these are generalizations; there are exceptions to these rules]...

5. Describe the primary venous drainage of the upper limb.

The veins of the upper limb may be loosely categorized as either superficial or deep, with the major (largest) veins of the upper limb being superficial.

Deep veins are typically accompanying veins (venae comitantes) of arteries (e.g. radial vv., ulnar vv., brachial vv., etc.). Deep veins, therefore, follow a very similar pattern of distribution as the arteries they accompany. Most deep veins of the upper limb return to either the basilic v., or its direct continuation, the axillary v.

The superficial hand and forearm are drained laterally (thumb side) by the cephalic v. and medially by the basilic v. The cephalic and basilic vv. course through the subcutaneous layer, often met with a variety of smaller tributaries. Often, blood from the cephalic v. may be shunted to the basilic v. from a frequently present median cubital v.

The point at which the basilic v. meets the brachial vv. near the origin of the axillary v. at the inferior/lateral margin of teres major m. The axillary v. becomes the subclavian v. at the lateral margin of the first rib (also the anatomical demarcation of the axillary & subclavian aa.).

6. Describe the lymphatic drainage of the upper limb.

Upper limb lymphatics fall into two categories: superficial (which follow veins), and deep (which follow arteries).

Lymph from the upper limb ultimately channels into the axillary group of nodes. Deep lymphatics channel through humeral nodes, then through central nodes, to apical nodes. Superficial lymphatics channel through infraclavicular nodes before moving through apical nodes. Lymph from apical nodes channels through the subclavian trunk before re-entering venous blood at the venous angle.

Succinctly:

7. Describe the nerve supply of the muscular compartments of the upper limb, and consider the effect a lesion would have on these nerves and the muscular compartments they serve.

Nearly all nerves in the upper limb arise from the brachial plexus, a network of nerve fibers. The nerve fibers come from the ventral primary rami (VPR) of C5-T1 levels to form the roots of the brachial plexus. These five roots variably contribute their nerve fibers into three trunks, which then split into six divisions (3 anterior, 3 posterior). The divisions recombine into three cords which eventually terminate in five main terminal branches (nerves) that supply the upper limb. A picture is worth a thousand words here. The key concept is that the spinal nerves (C5-T1) form a network that allows the terminal branches/nerves to consist of nerve fibers from multiple spinal cord levels.

Each compartment of muscles is primarily supplied by a single nerve (although the nerve has multiple spinal cord levels represented). Below is a basic summary – exceptions and deeper level details are not included here.

Shoulder:

Deltoid muscle – axillary n.

Arm:

Anterior (flexor) compartment – musculocutaneous n. The musculocutaneous n. pierces through the coracobrachialis muscle, gives motor supply to the anterior compartment of the arm, and then continues on into the forearm as a cutaneous n. of the lateral forearm.

Extensor (extensor) compartment – radial n. The radial n. runs deep in the posterior region directly on the posterior humerus. The radial n. runs with the deep artery of the arm in the radial groove of the humerus, where it is vulnerable to injury if the shaft of the humerus is injured.

Forearm:

Anterior (flexor/pronation) compartment – median n. & ulnar n. The median n. supplies all of the muscles of the anterior compartment of the forearm except for 1.5 muscles: the flexor carpi ulnaris m. and half of the flexor digitorum profundus m. (which are innervated by the ulnar n.). The median n. continues into the hand (crossing the wrist through the carpal tunnel, where it is vulnerable to compression from inflammation of the other structures in the “tunnel”) and supplies the thenar muscles of the hand. The ulnar n. supplies 1.5 muscles in the anterior forearm – the flexor carpi ulnaris m. (ulnar-side wrist flexor) and the ulnar half of the flexor digitorum profundus m. (deep flexors of the digits). The ulnar n. continues into the hand to supply most of the hand muscles. Note the location of the ulnar nerve as it runs through behind the medial epicondyle of the humerus leaves is vulnerable to compression against the bone; you know this spot as your “funny bone”.

Posterior (extensor/supination) compartment – radial n. The radial n. continues from the posterior compartment of the arm across the lateral epicondyle of the humerus (on the anterior surface) where it branches into a deep muscular branch supplying the muscles of the posterior forearm (extensors of the wrist, MC, PIP, & DIP) and a superficial cutaneous branch where it supplies the skin of the dorsum of the hand and fingers.

8. Diagram the cutaneous peripheral maps of the upper limb.

The peripheral cutaneous nerves of the upper limb are predominantly derived from the brachial plexus; however, the shoulder region has a substantial supply from the supraclavicular nn. of the cervical plexus.