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Anatomy of Hand

Introduction

The hand in the human body is made up of the wrist, palm, and fingers. The most flexiblepart of the human skeleton, the hand enables us to perform many of our daily activities.When our hand and wrist are not functioning 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
  • Numerous Blood vessels, nerves,and soft tissue

It is important to understand the normal anatomy of the hand in order to learn aboutdiseases and conditions that can affect our hands.

Skeletal Anatomy

The wrist is comprised of 8 bones calledcarpal bones. These wrist bones connectto 5 metacarpal bones that form the palmof the hand. Each metacarpal boneconnects to one finger or a thumb at ajoint called the metacarpophalangealjoint, or MCP joint. This joint is commonlyreferred to as the knuckle joint.

The bones in our fingers and thumb arecalled phalanges. Each finger has 3phalanges separated by two joints.

The first joint, closest to the knuckle joint,is the proximal interphalangeal joint orPIP joint. The second joint nearer the endof the finger is called the distalinterphalangeal joint, or DIP joint.The thumb in the human body only has 2phalanges 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: Shiny and smooth, cartilage allowssmooth movement where two bonescome in contact with each other.

Tendons: Tendons are soft tissue that connectsmuscles to bones to provide support.Extensor tendons enable each finger tostraighten.

Ligaments: Ligaments are strong rope like tissue thatconnects bones to other bones and helphold tendons in place providing stabilityto the joints. The volar plate is thestrongest ligament in the hand andprevents hyperextension of the PIP joint.

Muscles: Muscles are fibrous tissue capable ofcontracting to cause body movement.Interestingly, the fingers contain nomuscles. Small muscles originating fromthe carpal bones of the wrist areconnected to the finger bones withtendons.These muscles are responsible for movement of the thumb and littlefinger enabling the handto hold and grip items by allowing the thumb to move across the palm, a movement referredto as Thumb Opposition. The smallest muscles of the wrist and hand are responsible for finemotor movement of the fingers.

Nerves: Nerves are responsible for carrying signals back and forth from the brain to muscles in ourbody, enabling movement and sensation such as touch, pain, and hot or cold.The three main nerves responsible for hand and wrist movement all originate at theshoulder area and include the following:

  • Radial: The radial nerve runs down the thumb side of the forearm and provides sensation tothe back of the hand from the thumb to the third finger.
  • Median: The median nerve travels through the wrist tunnel, also called 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 Guyon’s tunnel formed bytwo carpal bones and the ligament that connects themtogether. The ulnar nerve suppliesfeeling to the little finger and half of the ring finger.

Blood Vessels: The two main vessels of the hand and wrist are

  • Radial Artery: The radial artery is thelargest artery supplying the hand andwrist area. Traveling across the front ofthe wrist, nearest the thumb, it is thisartery that is palpated when a pulse iscounted at the wrist.
  • Ulnar Artery: The ulnar artery travelsnext to the ulnar nerve through Guyon’scanal in the wrist. It supplies blood flowto the front of the hand, fingers andthumb. 

Bursae: Bursae are small fluid filled sacs thatdecrease friction between tendons andbone or skin. Bursae contain special cellscalled synovial cells that secrete alubricating fluid. When this fluid becomesinfected, a common painful conditionknown as Bursitis can develop.

Normal Movement

Biomechanics is a term to describe movement of the body.The fingers of the hand permit the following movements at themetacarpophalangeal joint (MCP) or knuckle joint.

  • Flexion: Moving the base of the finger towardsthe palm.
  • Extension: Moving the base of the fingers away fromthe palm.
  • Adduction: Moving the fingers toward the middlefinger.
  • Abduction:Moving the fingers away from the middlefinger.
  • Flexion:Moving the last two segments of thefinger towards the base of the fingers.
  • Extension:Moving the last two segments of thefinger away from the base of the fingers.

Biomechanics of the wrist include the following

  • Flexion: Moving the palm of the hand towards thefront of the forearm.
  • Extension: Moving the back of the hand towards theback of the forearm.
  • Adduction: Moving the pinky side of the handtoward the outer aspect of the forearm.
  • Abduction: Moving the thumb side of the handtoward the inner aspect of the forearm.

The thumb performs different movements at three separate joints. The carpometacarpaljoint is where the wrist bones, carpals, meet the metacarpals, the bones in the palm of thehand. At this articulation, the following movements can be performed

  • Abduction:Moving the bone below the thumbtowards the palm of the hand.
  • Extension:Moving the bone below the thumb awayfrom the hand.
  • Adduction:Moving the bone below the thumbtowards the back of the wrist.
  • Abduction: Moving the bone below the thumbtowards the front of the wrist.
  • Opposition: Moving the thumb across the palm of thehand touching the other fingers.

The following movements occur at the metacarpophalangeal joint or MCP joint at the baseof the thumb

  • Flexion: Moving the joint at the base of thethumb towards the heel of the hand.
  • Extension: Moving the joint at the base of thethumb away from the heel of the hand.
  • Adduction: Movement of the thumb base towardsthe back of the hand.
  • Abduction:Movement of the thumb base away fromthe back of the hand.

At the interphalangeal joint of the thumb or IP joint, the following movements can beperformed:

  • Flexion: Bending the top of the thumb towardsthe base of the thumb.
  • Extension hyperextension: Moving the top of the thumb away fromthe base of the thumb.