Hand Anatomy

Introduction:

The hand is a complex organ of the body at the end of the forelimb. It is the most flexible part of the skeletal system.The primary function of the hand is to hold and manipulate objects. In addition, they are used for feeling the touch sensation and play a role in sign language.There are two hands; each hand comprises a wrist, palm, backhand, and five fingers. The front or palm side of the hand is called the palmar side, and the back of the hand is called the dorsal side. A hand is composed of different bones, joints, muscles, ligaments, innervating nerves, and blood vessels that help in various movements and dexterity.

What Are the Bones and Joints That Form the Hand?

The hand consists of 27 bones and 27 joints.

• Bones:

  • Carpal Bones: The wrist of the hand contains eight bones called carpal bones. The carpal bones are arranged in two rows namely, the proximal and distal rows, with four bones in each row.

    • The proximal row comprises scaphoid, lunate, triquetrum, and pisiform (moving from thumb side to little finger) and is connected to the bones in the palm.

    • The distal row is connected to the long bones of the forearm, and the names of these bones are trapezium, trapezoid, capitate, and hamate (moving from thumb side to little finger).

  • Metacarpal Bones: The wrist bones that connect to the five tubular bones in the palm are called the metacarpals. They are present between the wrist and the fingers. Each metacarpal bone has a head, body, and base.

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  • Phalanges: The bones in the fingers are called phalanges. Thumb has two phalanges, and the other fingers have three phalanges each. The outermost bone near the nail is called the distal phalanx; the mid one is the middle phalanx, and the innermost bone is the proximal phalanx.

• Joints:

  • Wrist Joint: It is also called the radiocarpal joint, where the distal end of the radius bone (long bone of the forearm) articulates with the three carpal bones in the proximal row; scaphoid, lunate, triquetrum. The joint surfaces between proximal and distal rows of carpal bones are called the midcarpal joints. The plane joint between the carpal bones is called an intercarpal joint.

  • Carpometacarpal Joint: Here, the base of the metacarpals articulates with the distal row of the carpal bones. The following are the bone articulations in carpometacarpal joints:

    • First metacarpal bone to trapezium.

    • Second metacarpal bone to trapezium, trapezoid, capitate.

    • Third metacarpal bone to capitate.

    • Fourth metacarpal bone to capitate, hamate.

    • Fifth metacarpal bone to hamate.

• Metacarpophalangeal Joint: The head of the metacarpals articulate with the base of the proximal phalanges.

• Interphalangeal Joint: There are about nine joints articulating between the phalanges, which are called the interphalangeal joints.

What Are the Muscles Present in the Hand?

The muscles of the hand are skeletal muscles. These are connected to the bones and are responsible for movement. The two groups of muscles present in the hand are, extrinsic and intrinsic muscles.

1. Extrinsic Muscles:

Extrinsic muscles are extensors and flexors. They are long muscles located in the forearm and inserted in the hand skeleton, hence the name extrinsic.

• Extensor Muscle: Extensors are the muscles of extension, a movement of the joint where the angle between the two bones is increased. The action of the extensors results in the straightening of the hand.

• Flexor Muscle: Flexors are the muscles of flexion, a movement of the joint where the angle between the two bones is decreased. The action of the flexor muscle results in the bending of the hand.

2. Intrinsic Muscles:

Intrinsic muscles are thenar, hypothenar, lumbrical, and interossei. They are small muscles located within the hand itself.

• Thenar Muscles: The thenar muscles or the thenar eminence is a collection of three muscles constituting the thumb on the palmar side. The action of the thenar muscles results in the movement of the thumb.

• Hypothenar Muscles: The hypothenar muscles are the collection of three muscles constituting the little finger on the palmar side. The action of hypothenar muscles results in the movement of the little finger.

• Lumbrical Muscles: The lumbricals are composed of four muscles that flex the metacarpophalangeal joints and extend the interphalangeal joints.

• Interossei Muscles: The interossei muscles are composed of four dorsal and three palmar muscles, present near the metacarpals comprising the middle three digits of the hand. The action of interossei muscles is to abduct (moving away from the midline) or adduct (moving towards the midline) the fingers.

What Are the Nerves Present in the Hand?

The nerves of the hand have both motor (carry impulses from the brain to muscles for movement) and sensory functions (carry senses of touch, heat, or pain from the hand to the brain).

The three main nerves of the hand are:

• Median Nerve: The median nerve innervates the thenar muscle group and the first and second lumbrical muscles. The branches of the median nerve provide sensation to the palm, thumb, index finger, middle finger, and part of the ring finger.

• Ulnar Nerve: The ulnar nerve innervates hypothenar, interossei, and the third and fourth lumbrical muscles. The branches of the ulnar nerve provide sensation to the little finger and half of the ring finger.

• Radial Nerve: The radial nerve provides sensation to the back of the hand from the thumb to the middle finger.

What Are the Blood Vessels Present in the Hand?

The blood vessels travel along with the nerve and supply blood to the hand. The two main arteries of the hand are the radial artery and ulnar artery. The pulse measured in the wrist is at the radial artery. The veins of the hand are called superficial veins since they are close to the skin. The two prominent superficial veins in the hand are cephalic and basilic veins. The lymphatic vessels of the hand drain into the superficial and deep lymphatic systems.

Conclusion:

The hand is the visible part of the brain, said Immanuel Kant. The hand is responsible for creative manifestations. The functional capability of the hand relates both to the structural characteristics and the control system of the brain. Hands can be affected by several diseases. Therefore, knowledge about hand anatomy is essential for the systematic assessment of hand disorders or injuries.

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