Injuries and Conditions: The Hand

Involved in almost every daily task, hands are a critical party of daily living and often among the most vulnerable parts of the musculoskeletal system as a result. The constant necessity and daily use of hands - in day-to-day tasks, as well as in sports, work and play - places them at increased risk for overuse conditions and injuries. If untreated, many of these injuries and conditions can result in more severe degenerative conditions over time.

It is this innate understanding of the small bones and joints of the hand that allow hand specialists to help patients preserve hand function throughout life.

Understanding the Hand
The fingers and thumb of the hand are referred to as phalanges. The phalanges have articulating joints (connecting bones that allow movement), one separating the top portion and bottom portion of each finger and thumb and one located where they meet the palm. The hand is comprised of a palm, or metacarpus, and five digits attached to the forearm by the wrist joint or carpus. There are five bones in the palm - one for each of the five digits (fingers and thumb).

Nearly a quarter of the motor cortex (controlling movement) in the human brain is dedicated to the hand muscles. There are approximately 34 muscles that move the fingers and thumb, over 120 known ligaments, 30 major joints, nearly 30 bones and numerous tendons connecting muscles to bone.

And while there are approximately 50 nerves in the hand, the three main nerves that carry the signals from the brain and prompt movement are the radial, median and ulnar nerves. These nerves begin at the shoulder and travel to the hand and fingers. The radial nerve runs along the outer thumb-side edge of the forearm and stops at the back of the hand, resting on the end of the radius bone. The median nerve runs through the carpal tunnel within the wrist and the ulnar nerve runs through the Guyon's Canal - a tunnel between two of the carpal bones, the pisiform and hamate, that connects ligament.

A large blood vessel called the radial artery accompanies these nerves and runs across the front of the wrist near the thumb. It is this artery that is often used to take a patient's pulse. The radial artery, together with a smaller artery called the ulnar artery - which is located along the ulnar nerve through the Guyon's canal - supply blood to the back of the hand, fingers and thumb.

The movements of the hand are achieved by extrinsic muscle groups, which consist of the long flexors and extensors, and by intrinsic muscle groups, which consist of the thenar and hypothenar - the thumb and the little finger. The muscles controlling finger function are located in the middle of the palm and extend to the mid forearm or elbow. These muscles are connected to the finger bones by the tendons and serve as a type of pulley moving the fingers.

The collateral ligaments are located on both sides of each finger and thumb joint, providing joint stabilization. The strongest of these is the volar plate, which joins the proximal phalanx with the middle phalanx on the palmar side of the joint. The extensor tendons allow the finger joints to extend out straight.

The primary knuckle joints are the result of the connection between the phalanges to the metacarpals (bones at the base of the palm) and are called metacarpophalangeal joints (MCP joints). These joints allow the fingers and thumb to bend and straight. The three phalanges in each finger are separated by two interphalangeal (IP) joints, the proximal (PIP) and the distal interphalangeal (DIP) joints, which also facilitates bending and straightening. The end of each joint is covered with articular cartilage, which serves as a shock absorber as the bones move against one another, or articulate.

The Thumb
The thumb is a fascinating part of the hand, capable of a broad range of motion. It is controlled by nine distinct muscles, which depend on the three major hand nerves to function. The thumb is able to attain a greater range of movement in many directions compared to the fingers - easily rotating 90 degrees compared to the average 45 degrees of the other fingers, as a result of the surface shapes of the two bones of which it is comprised.

The phalanges are connected to the longer first metacarpal bone in the hand. Utilizing muscles arranged around the first metacarpal, the joint at the base of the thumb is able to rotate and oppose the fingers, which easily enables grasping and pinching. And a band of fibrous tissue connecting the bones at the base of the thumb, called the ulnar collateral ligament, helps control thumb movement - preventing it from pointing excessively away from the hand.