Normal Hand Anatomy
It is important to understand the normal anatomy of the hand in order to learn about the diseases and conditions that can affect our hands. The hand in the human body is made up of the wrist, palm and fingers. The most flexible part of the human skeleton, the hand, enables us to perform many of our daily activities. When our hand and wrist do not function properly, daily activities such as driving a car, bathing and cooking can become impossible.
The hand’s complex anatomy consists of 27 bones, 27 joints, 34 muscles, over 100 ligaments and tendons, and numerous blood vessels, nerves and soft tissues.
The wrist is comprised of 8 bones called the carpal bones. These wrist bones connect to 5 metacarpal bones that form the palm of the hand. Each metacarpal bone connects to one finger or a thumb at a joint called the metacarpophalangeal joint or MCP joint. This joint is commonly referred to as the knuckle joint.
The bones in our fingers and thumb are called phalanges. Each finger has 3 phalanges, separated by two joints. The first joint, closest to the knuckle joint, is the proximal interphalangeal joint or PIP joint. The second joint closer the end of the finger is called the distal interphalangeal joint or DIP joint. The thumb in the human body has only 2 phalanges and one interphalangeal joint.
Soft tissue anatomy
Our hand and wrist bones are held in place and supported by various soft tissues. These include:
- Cartilage: Cartilage is a shiny and smooth tissue that lines the ends of bones in a joint to allow smooth movement.
- Tendons: Tendons are soft tissues that connect muscles to bones to provide support. Extensor tendons enable each finger to straighten.
- Ligaments: Ligaments are strong rope-like tissues that connect bones to other bones, providing stability to joints. The volar plate is the strongest ligament in the hand and prevents hyperextension of the PIP joint.
- Muscles: Muscles are fibrous tissues that contract and relax to enable body movement. Interestingly, the fingers contain no muscles. Small muscles in the carpal bones of the wrist are connected to the finger bones by tendons. These muscles are responsible for the movement of the thumb and little finger, enabling the hand to hold and grip items by allowing the thumb to move across the palm, a movement referred to as thumb opposition. The smallest muscles of the wrist and hand are responsible for the fine motor movements of the fingers.
- Nerves: Nerves are responsible for carrying signals back and forth from the brain to muscles in our body, enabling movement and sensations such as touch, pain, heat and cold. The three main nerves responsible for hand and wrist movement all originate at the shoulder and include:
- Radial: The radial nerve runs down the thumb side of the forearm and provides sensation to the back of the hand from the thumb to the third finger.
- Median: The median nerve travels through a tunnel in the wrist called the carpal tunnel, providing sensation to the thumb, index finger, long finger and part of the ring finger.
- Ulnar: The ulnar nerve travels through a tunnel in the wrist called the Guyon’s tunnel formed by two carpal bones and a ligament that connects them together. It supplies feeling to the little finger and half of the ring finger.
- Blood vessels: The two main blood vessels of the hand and wrist are
- Radial artery: The radial artery is the largest artery supplying the hand and wrist area. Traveling across the front of the wrist, nearest the thumb, it is this artery that is palpated when a pulse is counted at the wrist.
- Ulnar artery: The ulnar artery travels next to the ulnar nerve through the Guyon’s canal in the wrist. It supplies blood to the front of the hand, fingers and thumb.
- Bursae: Bursae are small fluid-filled sacs that reduce the friction between tendons and bone, or skin. Bursae contain special cells called synovial cells that secrete a lubricating fluid. When this fluid becomes infected, a common painful condition known as bursitis can develop.
Biomechanics is a term that describes the movement of the body.
The fingers of the hand permit the following movements at the metacarpophalangeal joint (MCP) or knuckle joint:
- Flexion: Movement of the base of the finger towards the palm.
- Extension: Movement of the base of the finger away from the palm.
- Adduction: Movement of the fingers toward the middle finger.
- Abduction: Movement of the fingers away from the middle finger.
- Flexion: Movement of the last two segments of the finger towards the base of the finger.
- Extension: Movement of the last two segments of the finger away from the base of the finger.
Biomechanics of the wrist include the following:
- Flexion: Movement of the palm of the hand towards the front of the forearm.
- Extension: Movement of the back of the hand towards the back of the forearm.
- Adduction: Movement of the pinky-side of the hand toward the outer aspect of the forearm.
- Abduction: Movement of the thumb-side of the hand toward the inner aspect of the forearm.
The thumb performs different movements at three separate joints. The carpometacarpal joint is where the carpals (wrist bones) meet the metacarpals, the bones in the palm of the hand. At this articulation, the following movements can be performed:
- Abduction: Movement of the bone below the thumb towards the palm of the hand.
- Extension: Movement of the bone below the thumb away from the hand.
- Adduction: Movement of the bone below the thumb towards the back of the wrist.
- Abduction: Movement of the bone below the thumb towards the front of the wrist.
- Opposition: Movement of the thumb across the palm of the hand touching the other fingers.
The following movements occur at the MCP joint at the base of the thumb:
- Flexion: Movement of the joint at the base of the thumb towards the heel of the hand.
- Extension: Movement of the joint at the base of the thumb away from the heel of the hand.
- Adduction: Movement of the thumb base towards the back of the hand.
- Abduction: Movement of the thumb base away from the back of the hand.
At the interphalangeal joint of the thumb or IP joint, the following movements can be performed:
- Flexion: Bending the top of the thumb towards the base of the thumb.
- Extension hyperextension: Bending the top of the thumb away from the base of the thumb.