Soft Tissue Injuries of the Hand

The most common mechanisms of soft tissue injury of the hand are blunt trauma (eg, crush injury, contusions, abrasions), laceration, avulsion, ring avulsion, and burns. Besides skin and superficial tissues, the many muscles, ligaments, and tendons of the hand are vulnerable to injury, as are the nerves and blood vessels that supply these structures. Damage to these structures may create permanent functional and/or sensory deficits specific to the site of injury. ^{[1, 2, 3]}

Hand injuries are common and account for 5-10% of emergency department (ED) visits nationwide. In one study of upper extremity injuries and infections treated in EDs in the United States, the majority (37%) were soft tissue contusions. Over 50% of patients were male, and the most common age group was 18-44 years (44%), followed by those younger than 17 years (24%) and those 45-64 years (21%). ^[4]  Trauma accounts for the majority of these injuries. However, patients also present with complaints that are secondary to infection, burns, or overuse.

The complexity of the hand and the similarities in clinical presentation of different injuries make understanding of hand anatomy and function, good physical examination skills, and knowledge of indications for treatment indispensable for the emergency physician.

Complications of soft tissue hand injuries may include pain, stiffness, abscess, decreased range of motion, scar formation, and, rarely, loss of a digit or hand.

Terminology

Thorough knowledge of the anatomy and functions of the hand is required for proper diagnosis and treatment. Use of proper terminology prevents confusion that may compromise the care of patients with hand injuries. The following is a brief review of standard terminology and key anatomic structures:

• The hand and digits have palmar (volar) and dorsal surfaces and radial and ulnar borders.

• The digits are best described using their standard names rather than numbers.

• The proper names of the 5 digits beginning radially are thumb, index finger, long or middle finger, ring finger, and little finger.

Standard terminology also applies to motions and positions of the hand and digits, such as the following:

• Supination of the forearm positions the hand with the palmar surface superior. Pronation places the palmar surface inferior.

• Lateral motion of the hand, relative to the forearm, is described as radial deviation when the palm is supinated or ulnar deviation when the palm is pronated.

• Anterior and posterior motions of the hand, relative to the forearm, in its anatomic position are described as flexion and extension, respectively.

• Abduction of the digits refers to motion away from the middle finger and adduction to motions toward the middle finger.

• The fingers are in extension when held in the anatomic position. Movement of the digits dorsally is hyperextension, while movement toward the palm is flexion. In addition to flexion and extension, the thumb may move in toward the other digits (opposition) or away from them (retroposition).

Anatomy

Three creases are present on the palmar surface of the digits. The distal and middle palmar creases correspond to the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints, respectively. The proximal digital palmar crease does not overlie a joint, as the MCP is more proximal. The long thenar crease partially encircles the thenar eminence and overlies the metacarpophalangeal (MCP) joint.

The wrist is composed of 8 carpal bones arranged in 2 rows of 4. The flexor retinaculum together with the carpal bones forms the carpal tunnel. The median nerve passes through the carpal tunnel with the tendons of the flexor digitorum profundus and superficialis. The ulnar nerve enters the hand passing between the hook of the hamate bone and the pisiform bone in the Guyon canal.

The metacarpal bones articulate with the wrist at the carpometacarpal (CMC) joints. The MCP joints are formed by the articulation of the metacarpal bones with the proximal phalanges (see the image below). The heads of the metacarpals form the knuckles, which are seen dorsally with the closed fist. The thumb has only one interphalangeal (IP) joint, while the rest of the digits have PIP and DIP joints.

Each of the MCP, PIP, and DIP joints has collateral ligaments, which provide lateral stability, and a volar plate, which prevents hyperextension. The volar plate is damaged frequently in subluxation and dislocation injuries.

The blood supply to the hand is derived from the ulnar and radial arteries, which form the superficial and deep palmar arterial arches by anastomosis. In the absence of vascular disease, either artery alone is sufficient to perfuse the entire hand in most of the population.

The muscles of the hand are designated as intrinsic or extrinsic. Extrinsic muscle bellies are in the forearm, and their tendons insert into the hand, while intrinsic muscles both arise in and insert in the hand. The muscles of the hand and digits also are named according to their function as either flexors or extensors.

The forearm flexors are extrinsic muscles of the hand. These muscles arise from the medial epicondyle of the humerus and include the following:

• Flexor carpi radialis

• Palmaris longus

• Flexor carpi ulnaris

• Flexor digitorum profundus

• Flexor digitorum superficialis

The tendons of flexor carpi radialis (FCR), palmaris longus, and flexor carpi ulnaris (FCU) are visible in the forearm (see the image below). The palmaris longus is absent in about 14% of the population. The median nerve lies between the palmaris longus and the flexor carpi radialis (to the ulnar side of the FCR). The flexor carpi ulnaris is a good landmark to locate the ulnar nerve and artery, which lie to the radial side of the FCU.

Flexion of the fingers is controlled by the flexor digitorum profundus and superficialis muscles. Both of the finger flexors lie on the ulnar side of the wrist with the median and ulnar nerves and the ulnar artery. The flexor carpi ulnaris and radialis flex the wrist when acting together and cause deviation to their respective active sides when contracting separately.

Branches of the median and ulnar nerves innervate all the intrinsic muscles of the hand. They can be divided into 3 groups: thenar (thumb), hypothenar (little finger), and lumbricals.

The thenar eminence is formed by the extensor pollicis brevis and the 3 short thenar muscles: the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. These muscles have short tendons that insert onto the proximal phalanx of the thumb. They are innervated by the recurrent branch of the median nerve. The superficial location of this branch renders it vulnerable to seemingly trivial trauma to the thenar eminence.

• The adductor pollicis adducts the thumb and, by doing so, provides grip. It is innervated by the ulnar nerve.

• The lumbricals flex the digits at the MCP joints and extend the IP joints. They place the fingers in the writing position.

• Seven interosseous muscles are located between the metacarpal bones: 3 are palmar and 4 are dorsal. The palmar interossei adduct, while the dorsal interossei abduct.

The forearm extensors consist of 11 muscles that extend the wrist, hand, and digits (see the image below). The forearm extensors pass into the hand in 6 compartments. All forearm extensors arise from the lateral epicondyle of the humerus. They are innervated by the radial nerve.

The median, ulnar, and radial nerves supply all of the sensory and motor innervation to the hand. The superficial volar and dorsal distributions of the sensory nerves are shown in the images below. The median nerve enters the hand via the carpal tunnel and often is involved in carpal tunnel syndrome. The median nerve sends motor fibers to the 3 short thenar muscles and the first and second lumbricals. The ulnar nerve sends motor fibers to the hypothenar muscles, the ulnar 2 lumbricals, the adductor pollicis, and all of the interosseous muscles. The radial nerve sends no motor branches to the intrinsic muscles of the hand.