The biceps brachii muscle is one of the chief muscles of the arm. The origin at the scapula and the insertion into the radius of the biceps brachii means it can act on both the shoulder joint and the elbow joint, which is why this muscle participates in a few movements of the arm. It derives its name from its two heads which merge in one unique distal body, defining the unusual structure of the muscle.

The biceps brachii muscle is supplied by the musculocutaneous nerve (C5-C6), a branch of the brachial plexus.

Arterial supply to the biceps brachii muscle varies considerably, coming from up to eight vessels originating from the brachial artery in the middle third of the arm.

In the shoulder joint both muscle heads partially enforce opposite movements. The long head pulls the arm away from the trunk (abduction) and turns it inwards (inward rotation) whereas the short head pulls the arm back towards the trunk (adduction). When both heads contract simultaneously it leads to an arm bend (flexion). In the elbow joint the muscle bends the forearm (flexion) and rotates it outwards (supination). The supination is most powerful in a flexed elbow. In addition to the movement functions, the biceps has the important task to support the humeral head within the shoulder joint. Its antagonist is the triceps brachii in the posterior compartment of the arm.

The majority of extensor carpi radialis longus originates from the lateral supracondylar ridge of humerus (distal third) and anterior aspect of the lateral intermuscular septum of the arm. A small portion of its fibres originate from the common extensor tendon attached to the lateral epicondyle of humerus. The fibres unite into a muscle belly which extends approximately to the middle of the forearm. The muscle belly is then replaced by a flat tendon that travels distally along the lateral surface of the radius, together with the tendon of extensor carpi radialis brevis. Both tendons course towards the radial styloid process, deep to the tendons of abductor pollicis longus and extensor pollicis brevis muscles. Proximal to the wrist, the tendons of extensor carpi radialis longus and brevis pass behind the radial styloid process within a common synovial sheath and continue along the radial groove deep to the extensor retinaculum of the wrist. At this level, the tendon of extensor carpi radialis longus is crossed by the tendon of extensor pollicis longus, after which it inserts on the posterior aspect of the base of the second metacarpal bone. Some tendon slips can insert into the first and third metacarpal bones.

Extensor carpi radialis longus receives innervation from the radial nerve, with contributions mainly from spinal nerves C5-C8. The radial nerve is a branch of the brachial plexus.

Extensor carpi radialis longus receives blood supply mainly from the radial artery. It directly supplies the distal part of the muscle, while the rest of the muscle receives blood from one of its radial recurrent branches. The brachial artery also supplies a small portion of the muscle via the radial collateral artery.

Extensor carpi radialis longus primarily acts on the wrist joint to produce two major actions: (1) wrist extension by working synergistically with extensor carpi radialis brevis and extensor carpi ulnaris, and (2) hand abduction (radial deviation), with the help of flexor carpi radialis.

A median nerve block is a simple, safe, and effective method of obtaining anaesthesia to the palmar aspect of the thumb, index finger, middle finger, radial portion of the palm and ring finger. The median nerve lies deep to the flexor retinaculum and about one centimetre under the skin of the volar wrist.
The palmaris longus tendon lies superficial to the retinaculum and is absent in up to 20% of patients.
The median nerve is located slightly lateral (radial) to the palmaris longus tendon and medial (ulnar) to the flexor carpi radialis tendon.

The procedure is as follows:
– Check sensation and motor function of the median nerve. Wear gloves and use appropriate barrier precautions.
– Locate the flexor carpi radialis and palmaris longus tendons, which become prominent when the patient flexes the wrist against resistance. The palmaris longus tendon is usually the more prominent of the two tendons.
– Needle-entry site: The needle will be inserted adjacent to the radial (lateral) border of the palmaris longus tendon just proximal to the proximal wrist crease. If the palmaris longus tendon is absent, the needle-entry site is about 1 cm ulnar to the flexor carpi radialis tendon.
– Cleanse the site with antiseptic solution. Place a skin wheal of anaesthetic, if one is being used, at the needle-entry site.
– Insert the needle perpendicularly through the skin and advance it slowly until a slight pop is felt as the needle penetrates the flexor retinaculum. When paraesthesia in the distribution of the median nerve confirms proper needle placement, withdraw the needle 1 to 2 mm.
– Aspirate to exclude intravascular placement and then slowly (i.e., over 30 to 60 seconds) inject about 3 mL of anaesthetic. If the patient does not feel paraesthesia, redirect the needle in an ulnar direction, under the palmaris longus tendon. If paraesthesia is still not felt, slowly inject 3 to 5 mL of anaesthetic in the proximity of the nerve 1 cm deep to the tendon.
– Allow about 5 to 10 minutes for the anaesthetic to take effect.

The radial artery lies lateral to the large tendon of the flexor carpi radialis muscle and anterior to the pronator quadratus at the distal end of the radius. The flexor carpi radialis muscle is used as a landmark in locating the pulse.

The brachialis muscle is a prime flexor of the forearm at the elbow joint. It is fusiform in shape and located in the anterior (flexor) compartment of the arm, deep to the biceps brachii. The brachialis is a broad muscle, with its broadest part located in the middle rather than at either of its extremities. It is sometimes divided into two parts, and may fuse with the fibres of the biceps brachii, coracobrachialis, or pronator teres muscles. It also functions to form part of the floor of the cubital fossa.

The brachialis is primarily supplied by the musculocutaneous nerve (C5, C6). In addition, a small lateral portion of the muscle is innervated by the radial nerve (C7).

Brachioradialis is a fusiform muscle located in the lateral part of the posterior forearm. Along with extensor carpi radialis brevis and extensor carpi radialis longus, it comprises the radial group of forearm muscles, which belong to the superficial layer of posterior forearm muscles. Although anatomically part of the posterior forearm muscles, which are known to be forearm extensors, brachioradialis’ fibre orientation enables it to rather flex the forearm, and aids in supination of the forearm at the radioulnar joint.

The brachioradialis muscle originates from the upper two-thirds of the lateral supracondylar ridge of humerus and the anterior surface of the lateral intermuscular septum of the arm. It slides over the lateral surface of the elbow joint, entering the anterolateral cubital area. The muscle fibres course inferiorly down the radial part of the anterior forearm, forming a thick tendon in approximately the middle of the forearm. This tendon then traverses the remainder of the forearm, inserting near the wrist, just proximal to the styloid process of radius.

Brachioradialis is innervated by the radial nerve (from the root values C5-C6) that stems from the posterior cord of the brachial plexus. Blood supply to the brachioradialis muscle comes from branches of the radial artery, radial recurrent artery and the radial collateral branch of the deep brachial artery.

The radial nerve and brachial artery are most likely to be damaged in humerus fractures. They are tethered together to the bone and cannot withstand the forces applied to it as a result of the displacement.

The medial half of the flexor digitorum profundus is innervated by the ulnar nerve. Paralysis of this muscle results in loss of flexion at the distal interphalangeal joint of the ring and little finger.
Flexion at the proximal interphalangeal joint is preserved as this is a function of the flexor digitorum superficialis which is innervated by the median nerve.
The ulnar nerve is not correct as ulnar nerve injury at the wrist would not affect the long flexors, and the injury must have been more proximal.

Extensor carpi ulnaris is a fusiform muscle in the posterior forearm. It spans between the elbow and base of the little finger. This muscle belongs to the superficial forearm extensor group, along with anconaeus, brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum and extensor digiti minimi muscles.

Like all the muscles of this compartment, extensor carpi ulnaris works as an extensor of the wrist. Moreover, due to its specific course, this muscle also acts to adduct the hand.

Extensor carpi ulnaris is innervated by the posterior interosseous nerve (C7, C8), a branch of the deep division of the radial nerve. The radial nerve stems from the posterior cord of the brachial plexus.

Blood supply to the extensor carpi ulnaris muscle is provided by branches of the radial recurrent and posterior interosseous arteries, which stem from the radial and ulnar arteries, respectively.

Abductor pollicis longus is a muscle found in the posterior compartment of the forearm. It is one of the five deep extensors in the forearm, along with the supinator, extensor pollicis brevis, extensor pollicis longus and extensor indicis.

Abductor pollicis longus is innervated by the posterior interosseous nerve (C7, C8), which is a continuation of the deep branch of the radial nerve. The radial nerve is a branch of the posterior cord of the brachial plexus.

Blood supply to the abductor pollicis longus muscle comes from the interosseous branches of the ulnar artery.

Acting alone or with abductor pollicis brevis, abductor pollicis longus pulls the thumb away from the palm. More specifically, it produces (mid-) extension and abduction of the thumb at the first metacarpophalangeal joint. This action is seen in activities such as bowling and shovelling.

Working together with the long and short extensors of the thumb, the muscle also helps to fully extend the thumb at the metacarpophalangeal joint. This action is important for loosening the hand grip, for example, when letting go of objects previously being held. Abductor pollicis longus also helps to abduct the hand (radial deviation) at the radiocarpal joint.

Flexion of the arm and flexion and supination of the forearm are weakened but not lost entirely due to the actions of the pectoralis major and deltoid, the brachioradialis and the supinator muscles respectively. There is loss of sensation over the lateral aspect of the forearm. Forearm pronation would not be affected as this is primarily produced by the pronator quadratus and pronator teres muscles, innervated by the median nerve.

Pronator quadratus is a small, square-shaped muscle that lies in the anterior compartment of the forearm. It arises from the distal fourth of the anterior surface of the ulna and inserts into the distal fourth of the anterior surface of the radius.
Pronator quadratus is innervated by the anterior interosseous nerve. It receives its blood supply from the anterior interosseous artery, which is a branch of the common interosseous artery, which in turn is a branch of the ulnar artery.
The main action of pronator quadratus is to assist pronator teres with pronation of the forearm. The deep fibres bind the radius and ulna together.
The pronator quadratus muscle highlighted in blue (adapted from Gray’s Anatomy)

The symptoms of median nerve injury include tingling or numbness in the forearm, thumb, and three adjacent fingers, as well as gripping weakness and the inability to move the thumb across the palm.

Because the thenar muscles and the flexor pollicis longus are paralyzed, flexion, abduction, and opposition of the thumb at the MCPJ and IPJ are gone.

Abductor pollicis brevis is innervated by the recurrent (thenar) branch of median nerve (root value C8 and T1).

Opponens pollicis is a muscle of thenar eminence, it is triangular in shape and lies deep to flexor pollicis brevis and abductor pollicis brevis. It originates from the flexor retinaculum, tubercles of scaphoid and trapezium, abductor pollicis longus tendon.

Its insertion is in the radial side of the base of proximal phalanx of thumb. It is supplied by the median nerve (C8, T1). It receives blood supply from superficial arch.

It flexes the metacarpal bone medially across the palm, also rotating it medially, causing opposition, the palmar aspect of the terminal segment of thumb contacts the flexor aspects of any other digit.

Flexor carpi radialis is innervated by the median nerve.

Damage to the central slip of the extensor digitorum tendon would result in loss of extension at the proximal interphalangeal joint resulting in a fixed flexion deformity of this joint, and hyperextension of the distal interphalangeal joint due to a loss of balancing forces. This is called the Boutonniere deformity.

Abductor digiti minimi is a short intrinsic muscle of the hand. It belongs to the group of muscles collectively called hypothenar muscles due to their acting on the 5th finger. Besides abductor digiti minimi, other hypothenar muscles include flexor digiti minimi brevis and opponens digiti minimi.

The main function of abductor digiti minimi involves abduction of the 5th finger, as well as flexion of its proximal phalanx. Along with other hypothenar muscles, this muscle forms the hypothenar eminence on the medial side of the palm.

Like other hypothenar muscles, abductor digiti minimi receives nervous supply from the deep branch of the ulnar nerve, derived from root values C8 and T1.

Abductor digiti minimi receives arterial blood supply from the palmar branch of ulnar artery, palmar digital artery, as well as branches of the ulnar side of the superficial palmar arch. The venous blood from the muscle is drained via the venous networks of the palm into the deep veins of the arm (vv. ulnares).

Fracture dislocations of the elbow appear extremely complex, and identification of the basic injury patterns can facilitate management. The simplest pattern of elbow fracture dislocation is posterior dislocation of the elbow with fracture of the radial head. Addition of a coronoid fracture, no matter how small, to elbow dislocation and radial head fracture is called the terrible triad of the elbow.

Damage to the axillary nerve will result in loss of abduction past about 15 degrees and weakness of lateral rotation due to paralysis of the deltoid and teres minor and loss of sensation over the regimental badge area on the upper lateral arm. The axillary nerve is most likely injured in fracture of the surgical neck of the humerus due to its course where it winds around this region together with the posterior humeral circumflex vessels.