Hand: Anatomy

Bones of the Hand

The bones of the hand consist of the following:

• Metacarpals Metacarpals The five cylindrical bones of the metacarpus, articulating with the carpal bones proximally and the phalanges of fingers distally. Wrist Joint: Anatomy
  • There are 5 metacarpal bones corresponding to each of the fingers.
  • The proximal portion is called the base.
  • The middle portion is called the shaft.
  • The distal portion is called the head.
• Phalanges 
  • Digits 2–5 have 3 phalanges: proximal, middle, and distal.
  • The 1st digit or the thumb only has 2 phalanges: proximal and distal.

Joints of the Hand

The joints of the hand and fingers consist of:

• Metacarpal-phalangeal joints, connecting the metacarpals Metacarpals The five cylindrical bones of the metacarpus, articulating with the carpal bones proximally and the phalanges of fingers distally. Wrist Joint: Anatomy to the fingers
• Interphalangeal joints, the hinge joints between the phalanges of the fingers

Intrinsic Muscles of the Hand

The muscles of the hand are divided into 2 groups based on muscle belly location:

1. Extrinsic: Muscle bellies are in the forearm Forearm The forearm is the region of the upper limb between the elbow and the wrist. The term “forearm” is used in anatomy to distinguish this area from the arm, a term that is commonly used to describe the entire upper limb. The forearm consists of 2 long bones (the radius and the ulna), the interosseous membrane, and multiple arteries, nerves, and muscles. Forearm: Anatomy; they provide strength and grip. (See the following section.)
2. Intrinsic: Muscle bellies are within the hand and are responsible for fine movement of the fingers.
   • Thenar muscles:
     • Form the thenar eminence
     • Responsible for multiple motions of the thumb
     • All innervated by the median nerve Median Nerve A major nerve of the upper extremity. In humans, the fibers of the median nerve originate in the lower cervical and upper thoracic spinal cord (usually C6 to T1), travel via the brachial plexus, and supply sensory and motor innervation to parts of the forearm and hand. Cubital Fossa: Anatomy (except for the adductor pollicis, which is innervated by the ulnar nerve Ulnar Nerve A major nerve of the upper extremity. In humans, the fibers of the ulnar nerve originate in the lower cervical and upper thoracic spinal cord (usually C7 to T1), travel via the medial cord of the brachial plexus, and supply sensory and motor innervation to parts of the hand and forearm. Axilla and Brachial Plexus: Anatomy)
   • Hypothenar muscles:
     • Form the hypothenar eminence
     • Responsible for multiple motions of the 5th digit (“little finger”)
     • All innervated by the ulnar nerve Ulnar Nerve A major nerve of the upper extremity. In humans, the fibers of the ulnar nerve originate in the lower cervical and upper thoracic spinal cord (usually C7 to T1), travel via the medial cord of the brachial plexus, and supply sensory and motor innervation to parts of the hand and forearm. Axilla and Brachial Plexus: Anatomy
   • Lumbricals: 
     • Link the flexor and extensor tendons of the fingers
     • Flex the MCP joints and contribute to the extension Extension Examination of the Upper Limbs of the interphalangeal joints
     • Lumbricals I and II (lateral side of the hand) are innervated by the median nerve Median Nerve A major nerve of the upper extremity. In humans, the fibers of the median nerve originate in the lower cervical and upper thoracic spinal cord (usually C6 to T1), travel via the brachial plexus, and supply sensory and motor innervation to parts of the forearm and hand. Cubital Fossa: Anatomy.
     • Lumbricals III and IV (medial side of the hand) are innervated by the ulnar nerve Ulnar Nerve A major nerve of the upper extremity. In humans, the fibers of the ulnar nerve originate in the lower cervical and upper thoracic spinal cord (usually C7 to T1), travel via the medial cord of the brachial plexus, and supply sensory and motor innervation to parts of the hand and forearm. Axilla and Brachial Plexus: Anatomy.
   • Interossei:
     • 4 dorsal interossei abduct the 2nd–5th fingers.
     • 3 palmar interossei adduct the 2nd–5th fingers.
     • Are innervated by the ulnar nerve Ulnar Nerve A major nerve of the upper extremity. In humans, the fibers of the ulnar nerve originate in the lower cervical and upper thoracic spinal cord (usually C7 to T1), travel via the medial cord of the brachial plexus, and supply sensory and motor innervation to parts of the hand and forearm. Axilla and Brachial Plexus: Anatomy

Thenar muscles

Hypothenar muscles

Lumbrical muscles

Interossei muscles

Extrinsic Muscles of the Hand

The extrinsic muscles of the hand have their origin and muscle bellies in the forearm Forearm The forearm is the region of the upper limb between the elbow and the wrist. The term “forearm” is used in anatomy to distinguish this area from the arm, a term that is commonly used to describe the entire upper limb. The forearm consists of 2 long bones (the radius and the ulna), the interosseous membrane, and multiple arteries, nerves, and muscles. Forearm: Anatomy and are divided into flexor (anterior compartment) and extensor (posterior compartment) muscles.

Extrinsic extensor muscles: superficial layer

Extrinsic extensor muscles: deep layer

Extrinsic flexor muscles: superficial layer

Extrinsic flexor muscles: deep layer

Movements of the Fingers

Extensor expansion

Also known as the extensor hood, dorsal expansion, dorsal hood, or dorsal aponeurosis of the hand and/or fingers. The extensor expansion comprises the tendons of the extensor muscles of the fingers and how these insert into the phalanges:

• At the distal end of the metacarpal, these tendons expand and merge to form an aponeurosis (“hood”), which covers:
  • Head of the metacarpal (dorsal and lateral sides)
  • Proximal phalanx (dorsal and lateral sides)
• At the proximal phalanx, the tendons divide into bands:
  • Lateral bands (2 per finger): pass on either side of the middle phalanx and insert into the distal phalanx, receiving tendons from the lumbricals, extensor indicis Extensor indicis Forearm: Anatomy, and dorsal and palmar interossei muscles
  • Central band (1 per finger): passes down the center of the proximal phalanx to insert into the base of the middle phalanx
  • Retinacular bands (2 per finger): pass obliquely on the lateral sides of the middle phalanx to connect the aponeuroses of palmar and dorsal sides of the finger

Flexor pulley system

Comprises the tendons of the flexor muscles of the fingers and how these insert into the phalanges, supported by a system of ligaments:

• Palmar aponeurosis
• 5 annular Annular Dermatologic Examination pulleys: made by transverse retinacular ligaments
• 3 cruciform pulleys: made by oblique cruciate ligaments
• Flexor muscles of the fingers:
  • Flexor digitorum superficialis Flexor digitorum superficialis Forearm: Anatomy tendons split at the proximal phalanx and insert laterally into the middle phalanx.
  • Flexor digitorum profundus Flexor digitorum profundus Forearm: Anatomy tendons pass centrally and insert into the distal phalanx.

Vessels of the Hand

Arterial supply

The arterial blood supply of the hand is provided by:

• Radial artery Radial Artery The direct continuation of the brachial trunk, originating at the bifurcation of the brachial artery opposite the neck of the radius. Its branches may be divided into three groups corresponding to the three regions in which the vessel is situated, the forearm, wrist, and hand. Forearm: Anatomy: palpated immediately lateral to the flexor carpi radialis Flexor carpi radialis Forearm: Anatomy tendon and just proximal to the wrist crease
• Ulnar artery Ulnar Artery The larger of the two terminal branches of the brachial artery, beginning about one centimeter distal to the bend of the elbow. Like the radial artery, its branches may be divided into three groups corresponding to their locations in the forearm, wrist, and hand. Forearm: Anatomy: palpated anterior medially on the wrist and passes into the hand through Guyon’s canal Guyon’s canal Wrist Joint: Anatomy
• Together, the radial and ulnar artery Ulnar Artery The larger of the two terminal branches of the brachial artery, beginning about one centimeter distal to the bend of the elbow. Like the radial artery, its branches may be divided into three groups corresponding to their locations in the forearm, wrist, and hand. Forearm: Anatomy form 2 arterial arches:
  • Superficial palmar arch: ulnar artery Ulnar Artery The larger of the two terminal branches of the brachial artery, beginning about one centimeter distal to the bend of the elbow. Like the radial artery, its branches may be divided into three groups corresponding to their locations in the forearm, wrist, and hand. Forearm: Anatomy + superficial palmar branch of the radial
  • Deep palmar arch: radial artery Radial Artery The direct continuation of the brachial trunk, originating at the bifurcation of the brachial artery opposite the neck of the radius. Its branches may be divided into three groups corresponding to the three regions in which the vessel is situated, the forearm, wrist, and hand. Forearm: Anatomy + deep palmar branch of the ulnar

Venous drainage

The venous drainage of the hand is the origin of the veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology of the upper extremity and begins in the dorsal and palmar venous network of the hand.

• Cephalic vein originates from the dorsal venous network in the area of the anatomical snuffbox.
• Basilic vein Basilic vein Arm: Anatomy originates from the ulnar side of the dorsal venous network of the hand.
• Median antebrachial vein originates from the palmar venous network of the hand.

Innervation of the Hand

The innervation of the hand is primarily via the median and ulnar nerves, with the radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy only contributing a small area of sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology innervation on the radial dorsal aspect of the hand.

Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology innervation

Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology innervation

Clinical Relevance

The following are common problems associated with the hand:

• Boxer’s fracture Fracture A fracture is a disruption of the cortex of any bone and periosteum and is commonly due to mechanical stress after an injury or accident. Open fractures due to trauma can be a medical emergency. Fractures are frequently associated with automobile accidents, workplace injuries, and trauma. Overview of Bone Fractures: fracture Fracture A fracture is a disruption of the cortex of any bone and periosteum and is commonly due to mechanical stress after an injury or accident. Open fractures due to trauma can be a medical emergency. Fractures are frequently associated with automobile accidents, workplace injuries, and trauma. Overview of Bone Fractures of the distal portion of the 5th metacarpal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types. Usually due to hitting an object with a closed fist. Symptoms include pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways and a depressed knuckle. Diagnosis is suspected based on the clinical exam and confirmed by X-rays X-rays X-rays are high-energy particles of electromagnetic radiation used in the medical field for the generation of anatomical images. X-rays are projected through the body of a patient and onto a film, and this technique is called conventional or projectional radiography. X-rays.
• Rheumatoid arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis: a majority of rheumatoid diseases affect the hand and finger joints. The synovial proliferation results in skeleton erosion Erosion Partial-thickness loss of the epidermis Generalized and Localized Rashes, destruction of the capsular ligamentous structures, and changes to tendon structure and function. Physical exam of the hand classically presents with ulnar deviation and subluxation Subluxation Radial Head Subluxation (Nursemaid’s Elbow) of the metacarpal phalangeal (MCP) joints, swan neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess deformities of the fingers, and Z deformity Deformity Examination of the Upper Limbs of the thumb.
• Swan neck deformity Swan Neck Deformity Rheumatoid Arthritis: characterized by flexion Flexion Examination of the Upper Limbs of the DIP joint and hyperextension of the PIP joint. Associated with rheumatoid arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis, trauma, and laceration Laceration Torn, ragged, mangled wounds. Blunt Chest Trauma.
• Boutonniere deformity Boutonniere Deformity Rheumatoid Arthritis: characterized by DIP joint extension Extension Examination of the Upper Limbs and PIP joint flexion Flexion Examination of the Upper Limbs. Secondary to rupture of the central slip of the extensor mechanism over the PIP joint. Associated with trauma (PIP joint dislocation) and rheumatoid arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis.
• Osteoarthritis Osteoarthritis Osteoarthritis (OA) is the most common form of arthritis, and is due to cartilage destruction and changes of the subchondral bone. The risk of developing this disorder increases with age, obesity, and repetitive joint use or trauma. Patients develop gradual joint pain, stiffness lasting < 30 minutes, and decreased range of motion. Osteoarthritis: a degenerative disorder of the articular cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage: Histology, subchondral bones, and other joint structures. Osteoarthritis Osteoarthritis Osteoarthritis (OA) is the most common form of arthritis, and is due to cartilage destruction and changes of the subchondral bone. The risk of developing this disorder increases with age, obesity, and repetitive joint use or trauma. Patients develop gradual joint pain, stiffness lasting < 30 minutes, and decreased range of motion. Osteoarthritis is the most common type of joint disease and the leading cause of disability Disability Determination of the degree of a physical, mental, or emotional handicap. The diagnosis is applied to legal qualification for benefits and income under disability insurance and to eligibility for social security and workman’s compensation benefits. ABCDE Assessment in older adults. The main risk factors are family history Family History Adult Health Maintenance, female gender Gender Gender Dysphoria, past trauma to the involved joint, aging, and obesity Obesity Obesity is a condition associated with excess body weight, specifically with the deposition of excessive adipose tissue. Obesity is considered a global epidemic. Major influences come from the western diet and sedentary lifestyles, but the exact mechanisms likely include a mixture of genetic and environmental factors. Obesity.
  • Heberden’s nodes (DIP): usually secondary to primary osteoarthritis Primary Osteoarthritis Osteoarthritis of the DIP joints. Associated with mucous cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change of the DIP joint and nail deformities. May contribute to joint contracture and deformity Deformity Examination of the Upper Limbs.
  • Bouchard’s nodes (PIP): hard, bony outgrowths or gelatinous cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change on the PIP joints. Less commonly, Bouchard’s nodes may be seen in rheumatoid arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis. May contribute to joint contracture and deformity Deformity Examination of the Upper Limbs.