Finger, Hand, Wrist & Elbow Anatomy

Our hands are a brilliant combination of art, physiology, psychology, movement, senses and very complex on top of being very functional. It’s health and integrity is downright essential for any and all of our daily functions and needs.

Without our hands, it makes it very hard to navigate and participate in the world.

  • The upper limb has sacrificed locomotor function and stability for mobility, dexterity and precision.
  • The hand, positioned at the end of the upper limb, is a combination of complex joints whose function is to manipulate, grip and grasp, all made possible by the opposing movement of the thumb.
  • Some biologists believe that the development of the human hand lead indirectly to the development of our large and complex brain. The hand’s existence promoted brain development by allowing humans to manipulate, interact with, explore, and gain information from the environment. A more complex brain permitted us in turn to make and use tools and to develop language leading to an elaborate system of shared meanings, what we know as culture.

Wrist Anatomy

The hand and wrist have a total of 27 bones arranged to roll, spin and slide; allowing the hand to explore and control the environment and objects.

  • the pisiform, triquetrum, lunate and scaphoid on the upper end of the wrist
  • the hamate, capitate, trapezoid and trapezium on the lower side of the hand.

Other bones of the hand are:

  • the metacarpals – the five bones that comprise the middle part of the hand
  • the phalanges (singular phalanx) – the 14 narrow bones that make up the fingers of each hand. Each finger has three phalanges (the distal, middle, and proximal); the thumb has two.

The hand is divided into three regions

  • Proximal region of the hand is the carpus (wrist)
  • The middle region the metacarpus (palm)
  • The distal region the phalanges (fingers).

The Carpus

  • The carpus controls length-tension relationships in the multiarticular hand muscles and to allow fine adjustment of grip.
  • Three of the bones in the proximal row articulate with the radius forming the radiocarpal joint and distally with the distal carpal forming the midcarpal joint.
  • The four carpal bones in the distal row articulate with the bases of the five metacarpal bones forming the carpometacarpal joints
  • The joints formed between the carpal bones are known as the intercarpal joints and most are of the plane synovial type, as the bones interlock with each other the rows are sometimes referred to as two single synovial joints.

The arrangement of the bones and ligaments allows very little movement between bones, but they do slide contributing to the finer movements of the wrist.

The exception to this is the capitate which has a larger range of movement.

Proximal Row

  • Scaphoid – (boat like)– anterior surface palpable tubercle. Articulates proximally with radius, medially with lunate and distally with the head of the capitate.  It is a common site of fracture- 70% of all carpal fractures, often injured by a fall onto an outstretched limb
  • Lunate – (moon shaped) – Its palmar surface is smooth and convex and is larger than its dorsal surface.  Proximally it articulates with the radius and articular disc, medially with the triquetrum, laterally with the scaphoid and distally with the head of the capitate
  • Triquetrum – (three cornered) – Nestles in the space between the lunate and hamate.  When the hand is adducted it enters the radiocarpal joint.
  • Pisiform – (pea shaped) = a small round bone found in the tendon of flexor carpi ulnaris.  It articulates with the palmar surface of the triquetrum.   The anterior surface projects distally and laterally forming the medial part of the carpal tunnel.

Distal Row

  • Trapezium – four sided figures with no two sides parallel – the most irregular, with a palpable tubercle and groove anterior medially. It articulates proximally with the scaphoid and medially with the trapezoid.  Its articular surface is saddle-shaped and contributes to the mobility of the carpometacarpal joint of the thumb
  • Trapezoid – four sided figure with two parallel sides – Articulates distally with the second metacarpal, laterally with the trapezium, proximally with the scaphoid and medially with the capitate
  • Capitate – head shaped – The largest of all the carpal bones sitting centrally and articulating with the lunate and scaphoid, medially with the hamate and laterally with the trapezoid.  The distal surface articulates mainly with the base of the third metacarpal but also by narrow surfaces with the bases of the second and fourth metacarpals.
  • Hamate – hooked – This is wedge shaped with a curved palpable hook projecting from the palmar surface near the base of the fifth metacarpal.

The following pneumonic makes it easy to remember the position of each bone, naming the carpal bones in a circle, starting with the proximal row from the scaphoid towards the pinky (small finger) and then the distal row starting from the hamate towards the thumb:

  • So Long To Pinky, Here Comes The Thumb
  • Straight Line To Pinky, Here Comes The Thumb

The Carpal Tunnel – formed by the anterior concave space formed by the pisiform and hamate – on the ulnar side and the scaphoid and trapezium – on the radial side, with a roof-like covering of the flexor retinaculum (strong fibrous bands of connective tissue).  The long flexor tendons of the digits and thumb and the median nerve pass through the carpal tunnel

The Metacarpus

The metacarpus, the palm of the hand, which is made up of five bones – the metacarpals.  The bones are numbered laterally, from the thumb, 1 – 5.  Each bone is long with a proximal quadrilateral base, a shaft (body) and a distal rounded head.  The base of the first metacarpal is saddle-shaped and articulates with the trapezium.  The base of the second metacarpal articulates with the trapezium, trapezoid and capitate. The base of the third metacarpal articulates with the capitate.  The bases of the fourth and fifth metacarpal articulate with the hamate.  The bases of the second to fifth metacarpals also articulate with each other.

The heads of the metacarpals, commonly known as knuckles, are smooth and rounded and extend onto the palmar surface – these become visible when the fist is clenched.  The head of the first metacarpal is wider than the others, having two sesamoid bones, usually found in the short tendons crossing the joint, which articulate with the palmar part of the joint surface.  The heads fit into a concavity on the base of the proximal phalanx at the metacarpophlangeal joints.

The Phalanges

The phalanges, the fingers, consist of 14 long bones.  Apart from the thumb (the pollex) each phalanx has three bones, the distal, middle and proximal phalanx – the thumb has only two distal and proximal.  As with the metacarpals, the phalanges are numbered 1-5 starting at the thumb.  The proximal phalanx is large and is concave for articulation with the head of the metacarpal.  The shaft is curved along its length being convex dorsally.  It is convex from side to side on its dorsal surface and flat on the palmar surface.  The distal end, the head, is smaller and convex to articulate with the next bone in sequence.  In order from the thumb, digits are also known as the index finger, middle finger, ring finger and little finger.

Joints of the Wrist and Hand

The wrist has two degrees of freedom, although some say three degrees of freedom because they include the movements of pronation and supination, which occur at the the radioulnar joint. The radioulnar joint is often referred to as a joint of the forearm but it is this articulation that gives the wrist more freedom of movement.  The true joints of the wrist and hand are listed in the table below.

Ligaments of the Wrist and Hand

Important ligaments of the hand are:

  • Collateral ligaments – strong ligaments on either side of the finger and thumb joints, which prevent sideways movement of the joint
  • Volar plate – a ligament that connects the proximal phalanx to the middle phalanx on the palm side of the joint. As the joint in the finger is straightened, this ligament tightens to keep the PIP joint from bending backward.
  • Radial and ulnar collateral ligaments – a pair of ligaments which bind the bones of the wrist and provide stability
  • Volar radiocarpal ligaments – a complex web of ligaments that support the palm side of the wrist
  • Dorsal radiocarpal ligaments – ligaments that support the back of the wrist
  • Ulnocarpal and radioulnar ligaments – two sets of ligaments that provide the main support for the wrist.

The stability of the wrist is provided by ligaments (see table); on the palmar aspect is the flexor retinaculum which together with the carpal bones forms a canal – the carpal tunnel – which nerves, muscles and blood vessels run through, it is this area that is involved in carpal tunnel syndrome.

Movements of the Wrist and Hand

Thirty-four muscles act on the hand.

  • Intrinsic muscles of the hand contain the origin and insertions within the carpal and metacarpal bones.
  • Muscles originating in the forearm are the extrinsic muscles of the hand.
  • The intrinsic muscles of the hand provide the fine motor movements while the extrinsic muscles permit strength.

A common rule of thumb is that any muscle tendon that crosses a joint will act on that joint. For example, muscles of the forearm that cross the carpometacarpal joint will produce flexion or extension at the wrist joint. [11]

Grip & Grasp

Grip .jpgTypes of grasp. Two types of grasp are differentiated according to the position and mobility of thumb, CMC, and MP joints.
  1. POWER grasp (The terms grasp, grip, and prehension are interchangeable.) (The adductor pollicis stabilizes an object against the palm; the hand’s position is static.)
    • Cylindrical grip (fist grasp is a small diameter cylindrical grasp)
    • Spherical grip
    • Hook grip (MP extended with flattening of transverse arch; the person may or may include the thumb in this grasp)
    • Lateral prehension (this can be a power grip if the thumb is adducted, a precision grip if the thumb is abducted).
  2. PRECISION (Muscles are active that abduct or oppose the thumb; the hand’s position is dynamic.)
    • Palmar prehension (pulp to pulp), includes ‘chuck’ or tripod grips
    • Bip-to-tip (with FDP active to maintain DIP flex)
    • Lateral prehension (pad-to-side; key grip)

Arches of the Hand

The hand, when in at rest, forms a hollow at the palm, with the fingers flexed and the thumb in slight opposition. There are three distinct arches, longitudinal, oblique and transverse, that are formed by the bones, ligaments and tendons these are of vital importance when gripping and manipulating objects.

Longitudinal Arches (Brown)

These are known as the carpometacarpophalangeal arches run from the wrist to each digit. The arches are concave with the keystone laying level with the metacarpophalangeal joint; muscular imbalance at this point can decrease the concavity of the arch. The most important of these arches are the ones of the index finger and middles finger which are used when gripping objects, especially the arch formed to the index finger which we use when holding and using objects such as a pen.

Oblique Arch (Red)

These arches runs from the base of the hypothenar eminence to the head of the second metacarpal. It lies in parallel the palmar crease ‘life-line’ and is evident when holding tools or a tennis racquet.

Transverse Arches (Light green and Dark Green)

This arches lays across the palm and is maintained by the retinaculum. It runs from the wrist where its shape is maintained by the retinaculum and therefore more rigid, distally to the metacarpal heads where it is much shallower and more flexible.

Functional Position of the Hand

When therapists immobilize a patient’s hand, they often position it this way. During a period of immobilization, the resting lengths of the hand’s ligaments and muscles change. This hand position provides the best balance of resting length and force production so the hand can function when the patient mobilizes it again.

Wrist

  • Extended 20 degrees
  • Ulnarly deviated 10 degrees

Digits 2 through 5

  • MP joints flexed 45degrees
  • PIP joints flexed 30-45 degrees
  • DIP joints flexed 10-20 degrees

Thumb

  • 1st CMC jt partially abducted and opposed
  • MP joint flexed 10 degrees
  • IP joint flexed 5 degrees

Elbow Anatomy

So our human elbow joint is where the distal humerus meets the proximal radius and ulna bones.

It is known as a trochleogingylomoid joint as it can flex and extend as a hinge (ginglymoid) joint as well as pivot around an axis (trochoid motion) known as pronation and supination.

The elbow joint is an extremely congruent and stable joint…

…and due to the complexity of the elbow, even after mild or severe injury, our elbow is more prone to stiffness than instability.

Elbow joint

The elbow joint is generally consisting of the articulation or joints of three (3) different bones, which are the:

  • humerus bone (bone of the upper arm)
  • radius bone (the long bone of the forearm on the outer side)
  • ulnar bone (the long bone of the forearm on the inner side)

They make two general joints:

Ulno-humeral Joint (Ulnar + Humerus Elbow Joint)

  • The ulnohumeral hinge joint is responsible for elbow flexion (bending) and extension (straightening).
  • The spool-shaped trochlea of the humerus articulates with the greater sigmoid arch of the proximal ulna.

Radiocapitellar Joint (Radius + Capitellum Elbow Joint)

  • The radiocapitellar joint is where the radius (radial bone) and humerus join.
  • It is partly responsible for pronation (turning palm to face down) and supination (turning palm to face up).
  • The capitellum of the lateral distal humerus is a spherical structure onto which the concave surface of the proximal radial head articulates.

Proximal Radio-ulnar Joint (Radius + Ulnar Elbow Joint)

  • The proximal radioulnar joint is a trochoid joint that mainly works / is for pronation or supination of the forearm.
  • The peripheral edge of the radial head articulates with the radial notch of the ulna.

Carrying Angle

  • The carrying angle is measured when the elbow is in full extension and full supination. It is an angle measured along the long axis of the humerus and ulna.
  • Usually in men, it is approximately 11-14° and women 13-16°.
  • In fact, this term “carrying angle” is appropriately named as it allows our arms to clear our hips as we walk and allows objects to be carried.

Movements of the Elbow

Flexion and Extension

Elbow flexion (bending) and extension (straightening) happens at the ulnohumeral joint. The normal range of movement is from 0-140° but note that “only” 30°-130° is required for most ADLs

Pronation and Supination

The radiocapitellar joint and proximal radioulnar joint are responsible for pronation and supination.

Normal ROM is considered approximately 180° (80°-90° pronation and 90° supination). 100° of movement (50° pronation and 50° supination) is considered adequate for most ADLs.

If pronation ROM is lost this can be compensated by using shoulder abduction.

But, there is no compensatory action for supination and as such a loss of supination ROM can pose a greater disability than a loss of pronation ROM.

Elbow Ligaments and Capsule

There are 2 main ligament complexes at the elbow namely the Medial and Lateral Collateral.

Elbow Medial Collateral Ligament Complex (MCLC)

The MCLC is comprised of the anterior bundle, posterior bundle and transverse ligament (the ligament of Cooper). The anterior bundle is considered to be the most important stabiliser of the elbow and provides valgus and posteromedial stability.

The anterior bundle is further divided into the anterior and posterior bands. The anterior band is more taught in extension and relaxes into flexion and the posterior band is taught in flexion and releases in extension.

This makes the anterior band more vulnerable to valgus stress when the elbow is extended and the posterior band of the AMCL more vulnerable to valgus stress when the elbow is flexed.

Elbow Lateral Collateral Ligament Complex (LCLC)

The LCLC is the primary stabiliser against varus and external rotation stresses. The lateral ulnar collateral ligament, the radial collateral ligament and the annular ligament form the LCLC.

The lateral ulnar collateral ligament is important in maintaining posterolateral rotatory stability as well as stabilising against varus stresses. The radial collateral ligament also contributes to posterolateral rotational stability.

The Annular ligament surrounds the radial head but does not attach to it. It is am important stabiliser of the proximal radioulnar and radiocapitellar joint.

Joint Capsule

The joint capsule of the elbow surrounds all 3 joints.

There are thickening medially and laterally of the joint capsule that blensd with the MCLC and LCLC respectively and contributes tothe stability of the elbow.

Elbow Muscles

There are 4 main muscle groups at the elbow.

The anterior bicep group, the posterior tricep group, the lateral extensor-supinator group and the medial flexor-pronator group

Each muscle group applies a compressive load to the elbow joint when they contract.

Primary Elbow Flexors

  • Brachialis
  • Biceps brachii
  • Brachioradialis

Secondary Elbow Flexors

  • Pronator teres
  • Extensor carpi radialis longus
  • Flexor carpi radialis (at elbow angles 50 degrees or more)

Primary Elbow Extensors

  • Triceps
  • Anconeus
  • Secondary extensors
  • Flexor Carpi ulnaris
  • Extensor carpi ulnaris

Pronation

  • Pronator teres
  • Pronator quadratus

Supination

  • Mainly Biceps Assistance from supinator
  • Lesser degree finger and wrist extensors