Hand, Wrist and Arm Anatomy: Bones, Joints and Muscles

Wrist and Hand Anatomy

Wrist: The carpus consists of 8 bones divided into 2 rows. The first row includes the scaphoid, lunate, triquetrum and pisiform. The second row includes the trapezium, trapezoid, capitate and hamate.

Hand: The hand uses 2 types of bones: the metacarpals and the phalanges.

• Metacarpals: Long bones with a curved shape, numbered 1 to 5 from the thumb side to the little finger side.
• Phalanges: Long bones. There are 3 in each finger, except the thumb, which has 2 (proximal and distal).

Joints

Radiocarpal joint: The principal joint of the wrist is the radiocarpal joint, a monocondylar joint formed between the radius and the first row of carpal bones. It allows flexion (about 85–90°), extension, abduction (about 15°) and adduction (about 45–50°). Combined movements produce circumduction. Its articulations are with the carpal bones through arthrodial joints.

Carpometacarpal joints: The first carpometacarpal joint, between the trapezium and the first metacarpal, is a saddle joint. The others are arthrodial joints.

Metacarpophalangeal joints: These are ball-and-socket joints allowing flexion, extension, abduction, adduction and circumduction, as well as passive rotation.

Interphalangeal joints: These are trochlear or hinge joints that allow only flexion and extension.

Muscles of the Forearm and Hand

Pronator teres: Its origin is in the medial epicondyle of the humerus and the coronoid process of the ulna. It inserts on the lateral surface of the radius. It produces pronation of the forearm and can assist elbow flexion.

Flexor carpi radialis: Located on the anterior surface of the forearm. Its origin is in the medial epicondyle of the humerus and its insertion is on the base of the second metacarpal. It produces wrist flexion and radial deviation.

Flexor digitorum superficialis: Its origin is in the medial epicondyle of the humerus and the coronoid process of the ulna and the anterior surface of the radius. It sends 4 tendons through the carpal tunnel to the middle phalanges of the fingers 2 to 5. It produces flexion of the elbow, wrist, metacarpophalangeal joints and proximal interphalangeal joints.

Extensor digitorum: Located on the posterior surface, arising from the lateral epicondyle of the humerus. Its tendons pass to the wrist and split into 4 tendons that insert on the distal phalanges of fingers 2 to 5. It produces extension of the elbow, wrist, metacarpophalangeal joints and interphalangeal joints.

Movements of the Arm and Forearm

Flexion of the forearm (elbow): Biceps brachii, brachialis, brachioradialis, pronator teres, flexor carpi radialis, flexor carpi ulnaris, and flexor digitorum superficialis.

Extension of the forearm (elbow): Triceps brachii and anconeus.

Supination of the forearm: Biceps brachii, brachioradialis and supinator.

Muscles of the Thigh and Hip

Extension of the thigh: Gluteus maximus, semimembranosus, semitendinosus, long head of the biceps femoris and adductor magnus.

Flexion of the thigh: Iliopsoas, tensor fasciae latae, adductor longus, adductor brevis, sartorius, rectus femoris and pectineus.

Gluteus maximus: The largest gluteal muscle. Its origin is on the external iliac fossa, the posterior surface of the sacrum and the coccyx. It inserts on the gluteal tuberosity of the femur and partly into the iliotibial tract (fascia lata). Its fibers produce extension, lateral rotation and adduction of the thigh. Its maximum efficiency occurs when the hip is flexed between 45° and 90°.