The Hand and Wrist
The human hand is unique in its dexterity and range of abilities. Our hands hold, move, grasp, feel and manipulate the world and objects around us.
The anatomy of the hand and wrist includes bones, ligaments, tendons, muscles, blood vessels and nerves. The hand is joined to the arm by the wrist which consists of eight bones that enable the movement and strength needed to use our hands.
Hand and Wrist Motion
The wrist is a condyloid synovial joint. A synovial joint allows for smooth movements between adjacent bones. A condyloid synovial joint is where the joint is more oval in shape; allowing for movement along two axes.
This allows for several wide ranges of motion including flexion (up), extension (down), abduction (little finger side of hand moving away from body) and adduction (thumb side of hand moving towards body). Due to the longer (more distal) ulnar styloid process abduction is limited. The distal radioulnar joint enables pronation (palm facing down) and supination (palm facing up).
The thumb and fingers work together to give us a precision grip, in a similar fashion to that of tweezers, allowing us to pick up small objects or hold a pen in an extremely controlled and delicate way.
The metacarpal and phalangeal joints (or knuckle joints) allow for flexion and extension. The movement of the thumb is controlled by the carpometacarpal joint, which allows for flexion, extension abduction and adduction movements as well as opposition (where the thumb is moved towards the thumb to touch the other fingers) and reposition (where the thumb returns to anatomical position). The latter two positions allow for grasping.
Hand and Wrist Bones
The human hand and wrist consist of 27 bones: 8 carpal bones (bones of the wrist), 5 metacarpal bones (bones of the palm) and 14 phalanges (bones of the fingers and thumb).
The carpal bones join the radius and the ulna of the forearm to the metacarpal bones. The carpal bones are situated in two rows across the wrist. The proximal row is closest to the radius and ulna and the distal row is closest to the metacarpals.
The proximal row consists of the scaphoid, lunate, pisiform and triquetral. The distal row includes the hamate, capitate, trapezoid and trapezium. Each small carpal bone forms a joint with the adjacent bone, so the wrist is made up of a number of smaller joints. The proximal articular surfaces of carpal bones are covered with white, shiny, rubbery articular cartilage. This enables the joint surfaces to move against one another without causing damage and enables joints to move easily without causing damage and helps absorb shock. Cartilage is thinner in the wrist joint which typically does not have to bear a lot of weight.
The palm is made up of five metacarpal bones and the phalanges (bones of the finger) consist of the proximal phalanx, middle phalanx and distal phalanx.
Muscles of the Hand and Wrist
The muscles in the hand and wrist work together in an incredibly complex fashion. Not only do the muscles give your hand strength but they allow for your hand and fingers to move in an intricate manner.
The extrinsic muscles, located in the forearm, help produce a strong grip. The flexor digitorum profundus allows you to bend your index, middle, ring and little fingers. The flexor pollicis longus allows you to bend the tip of your thumb.
The intrinsic muscles, located in the hand, allow for fine motor functions such as writing. The intrinsic muscles consist of four muscle groups: the thenar, hypothenar, interossei and lumbrical muscles.
The thenar muscles are three muscles located at the base of the thumb which include the opponens pollicis muscle, which opposes the thumb, the abductor pollicis brevis, which abducts the thumb and the flexor pollicis brevis, which flexes the thumb.
Hypothenar muscles include the opponens digiti minimi, flexor digiti minimi brevis and the abductor digiti minimi; all of which control movement of the little finger.
The interossei muscles which are located between the metacarpal bones. The dorsal interossei muscles abduct the fingers at the metacarpophalangeal joints and the palmar interossei muscles adduct the fingers at the metacarpophalangeal joints.
The lumbricals muscles are four muscles that attach to the tendons of flexor digitorum profundus and flex the metacarpophalangeal joints and extend the interphalangeal joints.
Ligaments and Tendons of the Hand and Wrist
A ligament is fibrous connective tissue which attaches bone to bone, forming a joint capsule where they meet. This is a watertight sac containing a lubricating liquid called synovial fluid. The wrist ligaments are named according to where they are positioned in the joint and by which bones they connect.
Radiocarpal and ulnocarpal ligaments connect the radius and ulna. Palmar ligaments are positioned on the inside of the hand across the palm while a dorsal ligament supports the back of the hand.
The radial collateral and ulnar collateral ligaments support each side of the wrist, connecting the forearm. The radial collateral ligament originates at the radial styloid and attaches to the scaphoid bone. The ulnar collateral ligament originates at the ulnar styloid and is divided into two fasciculi which attach to the triquetral bone, pisiform and flexor retinaculum. The ulnar collateral ligament helps supports the small disc of cartilage where the wrist meets the ulna, known as the triangular fibrocartilage complex. This cushions the wrist joint, offers range of motion and stabilises wrist motion.
The palmar radiocarpal ligament supports the palmar side of the wrist, attaching the radius to the scaphoid, lunate, triquetrum. Some continue to the capitate bone.
Blood Vessels of the Hand and Wrist
If you’ve ever been out in the cold without gloves, you may have noticed your fingertips turn a shade of blue. This is due to your blood vessels narrowing and disrupting the blood flow to your fingertips.
Arteries are blood vessels that carry oxygen-rich blood from your heart to tissues of your body. The deep palmar arch extends from the radial artery, wraps around the thumb and stretches across the palm and supplies blood to the thumb and index finger. Extending from the ulnar artery, the superficial palmar arch also stretches across the palm. This artery communicates with the deep palmar arch and supplies blood to the fingers through the common digital arteries. The common digital arteries split near the web of the fingers to form the proper digital arteries, which split between two fingers (such as the index and middle fingers).
Veins return deoxygenated blood towards your heart. Cephalic and basilic veins are the two prominent superficial veins that originate at the dorsum of the hand at the dorsal venous arch. The cephalic vein also arises from the dorsal venous arch and forms the anatomical snuffbox (a triangular depression on the radial, dorsal aspect of the hand) along with the radial artery and a branch of the radial nerve.
Nerves of the Hand and Wrist
Nerves are responsible for carrying messages from the hand to your brain for sensation, reflexes and movement. For example, if you touch a hot stove, the nerves in your finger send a message to your brain for you to react and move your hand.
There are three major nerves that control our hand function: the radial nerve, median nerve, and ulnar nerve.
The radial nerve is responsible for wrist and finger extension and controlling sensation in the hand. It derives from the C4-T1 nerve fibres of the brachial plexus, a complex network of nerves that transmits signals from your spinal cord to your shoulder, arm and hand. The median nerve innervates the palmar side of the thumb, index and middle fingers and the radial side of the ring finger. It derives from the C6-T1 nerve fibres of the brachial plexus and sometimes contains fibres from C5. The ulnar nerve innervates the ring and little fingers and part of the anterior palm. It derives from the C8 and T1 nerve fibres of the brachial plexus.