Numerous muscles, ligaments, tendons, and sheaths can be found within the hand. The muscles are the structures that can contract, allowing movement of the bones in the hand. The ligaments are fibrous tissues that help bind together the joints in the hand. The sheaths are tubular structures that surround part of the fingers. The tendons connect muscles in the arm or hand to the bone to allow movement.

There are 19 bones in the human hand:

• 5 metacarpals
• 14 phalanges
  • 5 proximal phalanges
  • 4 middle phalanges
  • 5 distal phalanges
  • Each finger has 3 phalanges while the thumb has only 2 phalanges.

These bones form 19 joints in the hand:

• 5 carpometacarpal (CMC) joints between the metacarpals of the hand and the carpal bones of the wrist
• 5 metacarpal phalangeal (MP) joints between the metacarpals of the hand and proximal phalanges of the fingers
• 4 proximal interphalangeal (PIP) joints between the proximal and middle phalanges of the 4 fingers
• 4 distal interphalangeal (DIP) joints between the middle and distal phalanges of the 4 fingers
• 1 interphalangeal (IP) joint between the proximal and distal phalanges of the thumb.

All of these bones and joints help us move our hand to function in all of our everyday activities using our hands. Some common bone and joint conditions of the hand include osteoarthritis, rheumatoid arthritis, and hand or finger fracture.

Ligaments are strong fibrous bands of tissue that connect bone to bone. These provide stability and assist with mobility to joints throughout motion.

• Collateral Ligaments- on sides of finger and thumb joints that prevent sideways movements
• Volar Plate- Connects the proximal phalanx to the middle phalanx on the palm side of the finger. Prevents the PIP joint from bending backwards when straight

Some of the common conditions of ligaments in the hand include skier’s thumb, gamekeepers thumb, finger sprain, and finger dislocations.

There are two types of muscle groups that operate in the hand, the intrinsics (originate and terminate in the hand) and extrinsics (originate outside of the hand and terminate in the hand).

• Extrinsic Muscles:
  • Flexor Digitorum Superficialis (FDS)- begin in the elbow and attach on middle phalanges. They help to flex the wrist, MP and PIP joints. There are 4 FDS tendons.
  • Flexor Digitorum Profundus (FDP)- begin in the elbow and attach on distal phalanges. They help flex the wrist, MP, PIP, and DIP joints. There are 4 FDP tendons.
  • Extensor Digitorum Communis (EDC)- begin in the elbow and attach on the distal phalanges. These tendons straighten the index, middle, ring, and pinky fingers
  • Extensor Indicis (EI)- begins in the elbow and attaches to the distal phalanx of the index finger. It helps the EDC to straighten the index finger.
  • Extensor Digiti Minimi (EDM)- begin in the elbow and attach on the distal phalanx of the small finger. It helps the EDC to straighten the small finger. Only about 50% of people are born with this tendon.
  • Abductor Pollicis Longus (APL)- begins in the forearm at the radius, ulna, and interosseous membrane and attaches to the base of the first metacarpal and trapezium. It abducts and helps to extend the thumb.
  • Flexor Pollicis Longus (FPL)- begins in the forearm at the radius and interosseous membrane and attaches to the distal phalanx of the thumb. This bends the thumb at the interphalangeal (IP) joint.
  • Extensor Pollicis Longus (EPL)- begins in the forearm at the ulna and interosseous membrane and attaches to the distal phalanx of the thumb. This extends the thumb at the interphalangeal (IP) joint and also assists with metacarpal phalangeal (MP) joint.
  • Extensor Pollicis Brevis (EPB)- begins in the forearm at the radius and interosseous membrane and attaches to the base of the proximal phalanx of the thumb. This extends the metacarpal phalangeal (MP) and carpometacarpal joints (CMC).
• Intrinsic Muscles:
  • Thenar Muscles- These are in the palm, at the base of the thumb, and help produce finer movements of the thumb
    • Opponens Pollicis (OP)- begins at the trapezium and attaches to the thumb (1st) metacarpal. This helps oppose the thumb, which means it rotates medially and flexes the metacarpal in relation to the trapezium.
    • Abductor Pollicis Brevis (APB)- begins at trapezium and scaphoid and attaches to the proximal phalanx of the thumb. This abducts the thumb.
    • Flexor Pollicis Brevis (FPB)- begins at trapezium and attaches to the base of the proximal phalanx of the thumb. This flexes the metacarpal phalangeal (MP) joint of the thumb.
  • Hyopthenar Muscles- These are in the palm, at the base of the pinky
    • Opponens Digiti Minimi (ODM)- begins at the hook of the hamate carpal bone and attaches to the 5th metacarpal. This rotates the 5th metacarpal toward the palm of the hand to produce opposition.
    • Abductor Digiti Minimi (ADM)- begins at the pisiform and the tendon of the FCU and attaches to the base of the proximal phalanx of the small finger. This abducts the small finger.
    • Flexor Digiti Minimi Brevis (FDM)- begins at the hook of the hamate and attaches to the base of the proximal phalanx of the small finger. This flexes the metacarpal phalangeal (MCP) joint of the small finger.
  • Other muscles in the hand:
    • Lumbricals- There are 4 lumbricals in the hand, which link the flexor tendons to the extensor tendons. There is one lumbrical associated with each finger, except the thumb. These each begin at their designated flexor digitorum profundus (FDP) tendon for each finger and attach to the extensor hood. These flex the metacarpal phalangeal (MCP) joints while also extending the intercarpal phalangeal (IP) joints.
    • Interossei- These are located between each metacarpal in the hand. There are two types, 4 dorsal interossei and 3 volar (palmer) interossei.
      • Dorsal interossei begin at each side of the metacarpals and attach to the extensor hood and proximal phalanges. These abduct the fingers at the MCP joints and also assist the lumbricals in flexing the MCP joints while extending the IP joints.
      • Volar (palmar) interossei begin at each side of the metacarpals and attach to the extensor hood and proximal phalanges. These adduct the fingers at the MCP joints and also assist the lumbricals in flexing the MCP joints while extending the IP joints.
    • Adductor Pollicis- This muscle has two heads, the first begins at the 3rd metacarpal and the other begins at the capitate and metacarpals 2 and 3. It attaches to the proximal phalanx of the thumb. This muscle adducts the thumb.
    • Palmaris Brevis- Found in the tissue just below the skin on the small finger side of the hand, over the hypothenar muscles. This wrinkles the skin on the small finger side of the hand and deepens the curves, which allows for improved grip.

Some  of the common conditions that impact the tendons of the hand include trigger finger, mallet finger, boutonniere deformity, swan neck deformity, Rheumatoid arthritis, and tendon injuries/lacerations.

Peripheral nerves are tubes that extend out of the spinal cord and transmit electrical impulses that provide sensory and motor information to various stimuli and muscles to allow us to feel and move our body. There are a variety of nerves in the upper extremities, mostly of which originate from our neck, or cervical spine.

• Brachial Plexus- a group of nerves that control the muscles and the sensation throughout the arms.
  • There are various components of the brachial plexus including, roots, trunks, divisions, cords, and branches. An injury can occur at any of these components, causing various symptoms depending on the location.
  • Injuries can range from mild stretch to complete tears at the roots, which results in an arm with no sensation or ability to move or function.
  • Injuries often occur during accidents where the neck and arm move in opposite directions, as can occur in motor vehicle accidents or birth trauma.
• Radial Nerve- begins at the nerve roots C5, C6, C7, C8, and T1 in the brachial plexus. It wraps around the humerus and provides input to the triceps muscle, which extends the elbow. It travels around the outside of the elbow into the dorsal forearm and provides the input to the muscles that extend the wrist and fingers.
  • This nerve provides the sensation to the back of the hand and thumb, except the small and ring fingers.
  • Injuries can occur with injury to the humerus and from compression in the forearm, called “radial tunnel syndrome.” Injuries can cause weakness in the ability to extend the wrist and fingers to paralysis and the inability to extend the wrist and fingers, called wrist drop.
• Median Nerve- begins at the nerve roots C5, C6, C7, C8, and T1 in the brachial plexus. While this nerve travels along the inside of the upper arm, it does not provide any function or sensation until it crosses the elbow. In the forearm, it provides input to the muscles the flex the fingers and wrist and the muscles the pronate (palm down) the forearm. It also supplies the muscles in the thenar eminence (OP, FPB, and APB) and lumbricals 1 and 2.  It does not supply the FCU or the FDP muscles of the small and ring fingers, which is supplied by the ulnar nerve.
  • This nerve provides the sensation to the palm over the thenar muscles, the thumb, index, long, and half of the ring finger.
  • Injuries can cause weakness in forearm pronation, wrist flexion, and finger flexion. There may also be thenar muscle atrophy and difficulty with opposition of the thumb. Finally, there may be altered sensation such as numbness, tingling, or pins and needles to palm over the thenars, thumb, index, long, and half of the ring finger.
  • The median nerve further divides into the common palmar digital nerves. The first supplies lumbrical 2 and runs to the index and middle fingers where they divide into two to form the proper digital nerves on each side of the digit. The second goes to the middle and radial side of the ring fingers and divides into two to form the proper digital nerves on each side of the digit. It also communicates with a small branch of the ulnar nerve to lumbrical 3.
• Ulnar Nerve- begins at C8 and T1 nerve roots in the brachial plexus. It travels down the inside of the upper arm to the inside of the elbow. The “funny bone” feeling that travels down to the small and ring finger when you hit the inside of the elbow is actually the ulnar nerve. The inside of the elbow is a common point of compression, called cubital tunnel syndrome. It then continues to travel down the inside of the forearm into the side of the hand by the small finger. The ulnar nerve is responsible for providing input to the FDP muscles of the small and ring fingers (bends DIP joint of small and ring fingers), the FCU (flexes wrist and ulnarly deviates), hypothenar muscles, lumbricals 3 and 4, and the palmar and dorsal interossei.
  • This nerve provides sensation to the small finger side of the palm, the small finger and half of the ring finger, and the back (dorsal) side of the small finger.
  • Injuries can provide a variety of symptoms including altered sensations such as tingling, numbness, pins and needles to the small finger side of the palm, small finger, and half of the ring finger, weakness in many of the intrinsic muscles of the hand, causing decreased grip strength, and “clawing” of the small and ring fingers due to muscle imbalances.
  • The ulnar nerve further divides into the common palmar digital nerves, which then further divides into proper digital nerves of the ulnar side of the ring finger and the small finger.

Some  of the common conditions that impact the nerves of the hand include brachial plexus injuries, cubital tunnel syndrome, Guyon’s canal syndrome, carpal tunnel syndrome, radial tunnel syndrome, posterior interosseous nerve syndrome, and anterior interosseous nerve syndrome.