Hand – Bones, Ligaments, Muscles & Conditions
The hand and wrist is anatomically complex with 27 bones, 14 joints in the fingers alone, and a variety of joints where the palm meets the wrist and the wrist meets the forearm. The hand contains muscles that allow us to bend and straighten the fingers, and also ligaments and tendons that provide the stability and mobility that make the hand so dexterous. The front of the hand, or palm-side is referred to as the palmar side, while the back of the hand is referred to as the dorsal side.
Bone and Joint
The bones in the hand align precisely to provide a full range of motion and precision. When one of the bones is injured, it can force the entire hand out of alignment. There are 27 bones in the hand – eight in the wrist, called the carpals; five in the palm of the hand, called the metacarpals; and 14 bones in the fingers, called the proximal, middle, and distal phalanges. The two bones of the forearm, the radius and ulna also make up part of the wrist joint.
The ability to move our fingers with precision enables us to perform a wide variety of everyday tasks. This precise motion is made possible by the joints in the hand, which enable the fingers to bend. The joints in the fingers are the proximal interphalangeal (PIP) joints, located between the proximal and middle phalanges (finger bones), and the distal interphalangeal (DIP) joints, located between the middle and distal phalanges.
In addition to the joints in the fingers themselves, there are also metacarpophalangeal (MCP) joints in the hand where the proximal phalanges meet the metacarpal bones in the palm. In the wrist, each of the carpal bones has an associated joint – the radiocarpal, intercarpal, midcarpal, carpometacarpal, and intermetacarpal joints. There is also the distal radioulnar joint (DRUJ) between the radius and ulna (forearm bones).
Common hand bone and joint conditions include: Finger Fracture, Wrist Facture, Carpal Fracture, and Arthritis.
Muscles and Tendons
There are two muscle groups that work in the hand, the intrinsic and the extrinsic. The intrinsic muscles include the thenar muscle group and the hypothenar muscle group in the thumb and the pinky, the interossei muscles (dorsal and palmar), which originate between the metacarpal bones; and the lumbrical muscles, which originate at the deep flexor tendon. Intrinsic muscles only act on the fingers.
The extrinsic muscles are the long flexors and extensors, which run from the forearm into the hand, providing strength to the hand and wrist. The flexors enable the fingers to bend while the extensor muscles are used to straighten the fingers.
The hand contains the extensor digitorum, extensor indicis, extensor digiti minimi, flexor digitorum superficialis, and the flexor digitorum profundus. There are also extrinsic muscles that work only in the thumb; these include the flexor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and adbuctor pollicis longus.
In addition to the intrinsic and extrinsic muscles of the hand, the wrist also has its own set of muscles. Theyprovide strength and motion to the wrist, and in some cases also the elbow. These muscles include the extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, flexor carpi ulnaris, and Palmaris longus.
A tendon is part of the muscle that attaches muscle (it) to bone. The flexor tendons and extensor tendons are strong, fibrous tissues that are responsible for transferring the forces generated by the muscle to the bone, thus producing movement at the joint. The flexor tendons play a role in helping the fingers and wrist to bend downward, while the extensor tendons help the fingers straighten and the wrist to bend upward. When a tendon becomes irritated or inflamed it becomes painful, especially with movement. Inflammation of the tendon is called tendonitis
Common muscle (and tendon) conditions include: DeQuervain’s Tendonitis, Trigger Finger, Wrist Tendonitis, Extensor Tendonitis and Tendon Lacerations.
Ligaments are strong bands of tissue, made of collagen, that connect bone to bone. There are numerous ligaments that provide mobility and stability to the hand particularly the collateral, dorsal, volar, and interosseous ligaments. The wrist has a complex web of ligaments stabilizing the carpal bones. These include the dorsal intercarpal ligaments, the palmar intercarpal ligaments, the interosseous intercarpal ligaments, the pisohamate ligament, and the pisometacarpal ligament.
The collateral ligaments are a critical component in each of the joints in the fingers. Each phalangeal joint has two collateral ligaments, one on each side that provides stability, and prevent abnormal bending of these joints.
One of the most problematic areas of the hand is the carpal tunnel. The carpal tunnel is a structure in the wrist, formed by the carpal bones as the floor, and the transverse carpal ligament as the roof. Within the carpal tunnel are the median nerve, median artery and flexor tendons. These structures travel through the carpal tunnel from the forearm through the wrist and into the hand. The nerves and tendons that travel through the carpal tunnel are what give feeling and movement to the hand and fingers. When there is inflammation in the carpal tunnel, numbness or pain can occur in the hand.
Common ligament conditions in the hand include: Carpal Tunnel Syndrome, Wrist Sprain, Finger Sprain, Gamekeepers Thumb (aka Skier’s Thumb), and Finger Dislocations
A bursa is a fluid filled sac that decreases friction between two tissues. The radial bursa and the ulnar bursa pass through the flexor retinaculum in the wrist joint. Inflammation of these bursae can cause pain and stiffness in the wrist joint.
Common conditions of the bursa include Wrist Bursitis
There are three types of nerves in the hand, peripheral, afferent or sensory, and mixed nerves. A peripheral nerve is a specialized cord like structure that conducts electro chemical impulses from the spinal cord and brain to the body. There are three types of peripheral nerves that travel in the body. Afferent or sensory nerves conduct messages from the sensory receptors in the body to the spinal cord and brain, These nerves provide sensation, temperature, pain, pressure, and body position (proprioceptive) information to the brain. Efferent nerves conduct information from the brain and spinal cord to their target muscles and glands. They are responsible for delivering motor or movement instructions to the bodies musculoskeletal system. The third type of nerve is a mixed nerve that has both afferent and efferent properties.
Nerves are delicate structures, and can be injured by pressure, strain, stretching, or trauma (like being cut.) A nerve injury to the hand can cause weakness, loss of muscle function, pain, numbness, and decreased or abnormal sensation in the areas of the compromised nerve.
Common nerve conditions of the hand include: Ulnar Neuropathy, Carpal Tunnel Syndrome