Wrist Joints

Joints of the Wrist

• The wrist joints include the distal radioulnar, radiocarpal, midcarpal, and intercarpal joints
• The wrist complex controls length-tension relationships of hand muscles and allows fine adjustment of grip
• Wrist and hand structure and biomechanics vary greatly among individuals

Terminology

• Radial deviation is equivalent to abduction
• Ulnar deviation is equivalent to adduction
• Ventral, volar, and palmar all refer to anterior
• Dorsal (dorsum) refers to posterior
• Medial equates to ulnar
• Lateral equates to radial

Osteologic Features

Ulnar Tilt of Radius

• The distal end of the radius angles approximately 25 degrees toward the ulnar (medial) direction
• The ulnar tilt enables greater ulnar deviation than radial deviation
• Radial deviation is limited by the bony contact of lateral carpals with the radial styloid

Palmar Tilt of Radius

• The distal surface of the radius angles approximately 10 degrees in the palmar direction
• Palmar tilt contributes to greater wrist flexion than extension
• Distal radius fractures can impact the ulnar and/or palmar tilt, which alters the function of the distal radioulnar joint (DRUJ) or radiocarpal joint

Triangular Fibrocartilage Complex

• The components of the triangular fibrocartilage complex include:
  • Articular disc (triangular fibrocartilage)
  • Distal radioulnar joint capsular ligaments
  • Dorsal radioulnar ligament
  • Volar radioulnar ligament
  • Palmar ulnocarpal ligament
    • Ulnotriquetral
    • Ulnolunate
  • Ulnar collateral ligament
  • Fascial sheath enclosing extensor carpi ulnaris (ECU) tendon
• The triangular fibrocartilage complex functions as an extension of the distal radius at the wrist

Carpal Bones

• Carpal bones distal row is bound tightly by strong ligaments which provides a stable base for articulation with metacarpals
• The bones of the proximal row include scaphoid, lunate, triquetrum, and pisiform
• The bones of the distal row include trapezium, trapezoid, capitate, and hamate
• The proximal row of carpal bones is joined relatively loosely

Wrist Complex Joints

• Radiocarpal joint involves the radius and radioulnar disc articulating with the scaphoid, lunate, and triquetrum
• The midcarpal joint involves the scaphoid, lunate, and triquetrum articulating with the trapezium, trapezoid, capitate, and hamate

Radiocarpal Joint

• It is formed by the concave surface of the distal radius, the proximal carpal row, and the radioulnar disc of TFCC
• The lunate and triquetrum articulate with the TFCC
• The radiocarpal joint is a biaxial joint
• It allows for flexion, extension, radial deviation, and ulnar deviation
• The open-packed position is in neutral with slight ulnar deviation
• The close-packed position is in full extension with radial deviation

Radiocarpal Joint: Proximal Carpal Row

• The proximal carpals are interconnected by the scapholunate interosseous ligament and the lunotriquetral interosseous ligament
• The proximal carpal row and these ligaments function together as a single biconvex cartilage-covered joint surface
• The pisiform is anatomically part of the proximal row, but not part of the radiocarpal joint
• Pisiform functions as a sesamoid bone, which increases the moment arm of the flexor carpi ulnaris (FCU) tendon

Radiocarpal Joint ROM

• Average ROM:
  • Wrist flexion: 80°
  • Wrist extension: 70°
  • Wrist Radial Deviation (RD): 20°
  • Wrist Ulnar Deviation (UD): 30°
• Axial (compressive) loading of the carpals:
  • Scaphoid and lunate receive approximately 80% of the load
  • TFCC receives approximately 20% of the load.

Ulnar Variance

• Ulnar variance refers to the relative lengths of the distal articular surfaces of the radius and ulna and impacts wrist function
• Neutral ulnar variance (ulnar zero) has a difference between ulnar and radial length of 0-1mm
• Ulnar negative variance (negative ulnar variance) has a short ulna in comparison with the radius at the distal end
• Ulnar positive variance (positive ulnar variance) has a distal ulna that is long in relation to the distal radius.
• Ulnar variance impacts the distribution of compressive loads at the wrist
  • In a neutral variance, 80% of the load is distributed through the radius and 20% through the ulna
  • With a positive variance, radial load decreases and ulnar load increases
  • With a negative variance, radial load increases and ulnar load decreases.
• Factors that can alter ulnar variance Congenital
  • Madelung deformity or reverse Madelung deformity
  • Post fracture
  • DRUJ injuries
  • Growth plate disturbance
• Ulnar variance is associated with changes in TFCC thickness
  • Negative ulnar variance is associated with a thicker TFCC
  • Positive ulnar variance is associated with a thinner TFCC

Radioulnar Motion

• A small amount of ulnar movement occurs with open chain radioulnar joint motion
  • With pronation, the ulnar head moves distally and dorsally
  • With supination, the ulnar head moves proximally and volarly
• Compressive loading when the forearm is pronated can potentially cause greater stress through the TFCC in those with a positive ulnar variance

Radiocarpal Capsule & Ligaments

• A strong, somewhat loose joint capsule is present
• The joint is reinforced by capsular and intercapsular ligaments
• Most ligaments crossing the radiocarpal joint also contribute to stability at the midcarpal joint
• The radiocarpal joint has no muscles that act on it alone
• Forces acting on the pisiform by FCU aren't translated to triquetrum
• Forces transfer to hamate & 5th metacarpal via pisiform ligaments
• The FCU is the only muscle attaching to any of the bones of the proximal carpal row
• Radiocarpal joint motions stem from forces applied by ligaments and muscles attached to the distal carpal row and metacarpals.

Midcarpal Joint

• It is formed proximally by the scaphoid, lunate, and triquetrum
• It is formed distally by the trapezium, trapezoid, capitate, and hamate
• The articulation occurs between proximal and distal carpal rows
• The fibrous capsule and synovial lining is continuous with each intercarpal articulation and may also be continuous with some carpometacarpal (CMC) joints
• Joint surfaces are complex with an overall reciprocally concave-convex configuration
• The distal row moves functionally as a unit
• The open-packed position is in neutral or slight flexion with ulnar deviation
• The close-packed position is in full extension with ulnar deviation

Carpal Bones - Scaphoid

• It forms synovial joints with four other carpals and the radius
• Proximal pole: articulates with the scaphoid facet of the radius
• Distal pole: slightly rounded surface, articulates with the trapezium and trapezoid
• Projects obliquely in a palmar direction about 30°
• The distal-medial surface is deeply concave and articulates with the lateral half of the head of the capitate
• A small medial facet articulates with the lunate

Carpal Bones - Lunate

• This is the central bone of the proximal row and is wedged between the scaphoid and triquetrum
• It is the most inherently unstable carpal bone because it has a shape that lacks muscle attachments
• Proximal surface articulates with the radius
• The distal surface is deeply concave
• The articular surface of the lunate articulates with the medial 1/2 of the head of the capitate and part of the hamate

Carpal Bones - Triquetrum

• Most ulnarly positioned carpal
• Palpable just distal to ulnar styloid
• The lateral surface articulates with hamate
• Facet on palmar surface articulates with pisiform

Carpal Bones - Pisiform

• Articulates loosely with the triquetrum
• Easily movable and palpable
• Embedded within the FCU tendon
• Has characteristics of a sesamoid bone

Carpal Bones - Capitate

• It is the largest carpal bone located centrally within wrist
• The proximal surface articulates with the scaphoid & lunate
• The capitate is stabilized between trapezoid and hamate
• The distal surface is rigidly joined to the base of the 3rd metacarpal
• The capitate & 3rd metacarpal functions as single column and provides longitudinal stability to wrist & hand
• The axis of rotation for all wrist motions passes through capitate

Carpal Bones - Trapezium

• The proximal surface is slightly concave and articulates with the scaphoid
• The distal, saddle-shaped surface articulates with the base of the 1st metacarpal (1st carpometacarpal (CMC) joint)
• The saddle joint allows for wide ROM of thumb
• Tubercle on palmar surface is an attachment site for transverse carpal ligament
• Medial to palmar tubercle is groove for the FCR tendon

Carpal Bones - Trapezoid

• Small bone wedged between the capitate and trapezium
• Slightly concave proximal surface that articulates with the scaphoid
• Relatively firm articulation with the base of the 2nd metacarpal

Carpal Bones - Hamate

• A hook-like process that projects from the palmar surface
• The hook of the hamate is the attachment site for the transverse carpal ligament
• The base (distal surface) articulates with the 4th and 5th metacarpals
• Provides mobility to ulnar aspect of hand (esp with cupping of hand)
• The apex (proximal surface) contacts the lunate and wedges b/w capitate & triquetrum

Overall Ligamentous Support of Wrist

Ligamentous structures of the wrist are responsible for stability and guiding and checking motion between and among the carpals.

Ligaments

Extrinsic

• Connect carpals to radius or ulna proximally or carpals to metacarpals distally
• Provide majority of wrist stability

Intrinsic

• Attach carpal bones to other carpal bones
• Largely avascular
• Serve as rotational restraints of carpals
• Also know as interosseous or intercarpal ligaments

Volar Ligaments

• Generally stressed with wrist extension
• Volar radiocarpal ligament (3 bands)
• Radioscaphocapitate (radiocapitate)
• Short & long radiolunate (radiolunotriquetral)
• Radioscapholunate
• Ulnocarpal ligament complex
• TFCC & its associated ligaments
• Scapholunate ligament - A key factor in maintaining scaphoid stability
• Lunotriquetral ligament - Maintains stability between lunate & triquetrum
• Radial collateral ligament - Extension of volar radiocarpal ligament & capsule

Dorsal Ligaments

• Generally stressed/taut with wrist flexion
• Dorsal radiocarpal ligament
• Obliquely oriented
• Converges on triquetrum from distal radius
• possible attachments to lunate & lunotriquetral ligament Dorsal intercarpal ligament
• Runs horizontally from triquetrum to lunate, scaphoid, & trapezium
• Dorsal ligaments form a horizontal V shape that contributes to stability- Stabilizes the scaphoid during wrist ROM

Arthrokinematics

• Synchonous convex-on-concave rotation occurs at radiocarpal & midcarpal joints

Wrist Extension

Radiocarpal joint-

• Convex surface of lunate rolls dorsally on radius and slides palmarly
• The roll directs the lunate's distal surface dorsally, towards the direction of extension

Midcarpal joint

• Head of capitate rolls dorsally on lunate and slides in a palmar direction

Wrist Flexion

Radiocarpal joint

• Convex surface of lunate rolls palmarly on radius and slides dorsally
• The roll directs the lunate's distal surface palmarly

Midcarpal joint

• Head of the capitate rolls palmarly on the lunate and slides dorsally
• Full wrist extension lengthens palmar RC ligaments & muscles crossing palmar aspect of wrist
• Stability in full wrist extension is functionally important for activities that require loading the wrist/hand
• Full wrist flexion lengthens dorsal RC ligaments & muscles crossing dorsal aspect of wrist

Ulnar Deviation

Radiocarpal Joint

• Scaphoid, lunate, and triquetrum roll in an ulnar direction and slide radially

Midcarpal Joint

Capitate rolls in an ulnar direction and slides slightly radially

Radial Deviation

Radiocarpal Joint

• Scaphoid, lunate, & triquetrum roll in a radial direction and slide ulnarly
• Limited RD at this joint because of carpal impingement with radial styloid, The majority of RD occurs at midcarpal jt

Midcarpal Joint

capitate rolls in a radial direction and slides ulnarly

• When with UD, the proximal carpal row extends slightly, and with RD, the proximal carpal row flexes slightly

Loading Through Hand/Wrist/Forearm

• Compressive force transmitted primarily through wrist to radius, then large portion of force is transfered to the ulna through central band of the interosseous membrane, and it continues up humerus to shoulder

Musculature of the Wrist

• Designed for balance & control rather than maximizing torque
• Allows for adjustments to length–tension relationship of extrinsic hand muscles
• Wrist extensors function largely to position the hand for gripping activities
• FDP & FDS have a significant MA as wrist flexors
• Wrist extensors must counterbalance this torque during grip activities
• For optimal grip, wrist position is 30-35° extension, which is a position of optimal length-tension relationship of finger flexors

Forearm Muscles of the Wrist: Extensors

Prime Movers

• Extensor carpi radialis longus (ECRL)
• Extensor carpi radialis brevis (ECRB)
• Extensor carpi ulnaris (ECU)

Secondary Movers

• Extensor digitorum (ED)
• Extensor indicis (EI)
• Extensor digiti minimi (EDM)
• Extensor pollicis longus (EPL)

Extensor (Dorsal) Compartments of the Wrist

• 1st Compartment
  • Extensor pollicis brevis & abductor pollicis longus
• 2nd Compartment
  • Extensor carpi radialis longus & extensor carpi radialis brevis
• 3rd Compartment
  • Extensor pollicis longus
• 4th Compartment
  • Extensor digitorum & extensor indicis
• 5th Compartment
  • Extensor digit minimi
• 6th Compartment
  • Extensor carpi ulnaris

Forearm Muscles of the Wrist: Flexors

Primary Movers

• Flexor carpi radialis (FCR)
• Flexor carpi ulnaris (FCU)
• Palmaris longus (if present)

Secondary Movers

• Flexor digitorum profundus (FDP)
• Flexor digitorum superficialis (FDP)
• Flexor pollicis longus (FPL)
• Abductor pollicis longus (APL) – when wrist is in neutral position

Wrist Flexors

• Wrist flexors produce ~ 70% more isometric torque than wrist extensors related to greater total CSA of wrist flexor muscles
• Peak wrist flexion torque occurs at ~ 40° flexion
• FCU has greatest wrist flexion torque potential based on MA & CSA
• During active wrist flexion
• FCR & FCU act together as synergists to oppose each other’s RD and UD functions

Radial Deviators

• RD muscles generate ~15% more isometric torque than ulnar deviators
• Active wrist extension is typically coupled with RD
• In neutral wrist position
• ECRL & APL have largest product of CSA & MA for RD torque
• EPB has greatest MA of all radial deviators
• Resulting in relatively small force and torque production
• APL & EPB provide stability to radial side of the wrist

Radial Deviators

• Extensor carpi radialis longus
• Flexor carpi radialis longus
• Extensor pollicis longus
• Extensor pollicis brevis
• Flexor carpi radialis
• Abductor pollicis longus

Ulnar Deviators

• Extensor carpi ulnaris

• Flexor carpi ulnaris

• Flexion digitorum profundus

• Flexor digitorum superficialis

• Extensor digitorum

• The MA of the extensor carpi ulnaris (ECU) and flexor carpi ulnaris (FCU) makes them generate the most torque for ulnar deviation

Flexor Retinaculum: Transverse Carpal Ligament

Functions

• Attachment site for thenar & hypothenar muscles
• Helps maintain the transverse carpal arch Acts as restraint against bowstringing of extrinsic flexor tendons
• Protects the median nerve

Structures Covered

• Spans region between pisiform, hamate, scaphoid, & trapezium that creates carpal tunnel
• Proximal attachments are the Tubercle of scaphoid & pisiform
• Distal attachments are the Hook of the hamate & tubercle of trapezium

Deep Structures

Structures deep to retinaculum include the

• Flexor digitorum superficialis (FDS) tendons, Flexor digitorum profundus (FDP) tendons, and the Median nerve,
• Extensor pollicis longus (EPL),
• There is also Flexor carpi ulnaris (FCU)

Palmar Aponeurosis

• A dense fibrous structure just deep to subcutaneous tissue
• It is Continuous with the palmaris longus tendon & fascia covering the thenar & hypothenar muscles
• It Attaches distally to the transverse metacarpal ligaments & flexor tendon sheaths
• Provides some protection to the ulnar artery & nerve, digital vessels & nerves
• Splits into 4 slips as it travels toward fingers

Tunnel of Guyon

• This functions as the passageway for the ulnar nerve and artery into the hand- It is Located superficial to the flexor retinaculum
• Its Position is between the hook of the hamate & pisiform
• Its roof is formed by Palmar carpal ligament, Palmaris brevis muscle, and Palmar aponeurosis
• Its floor is formed by the Transverse carpal ligament, Pisohamate ligament, and Pisometacarpal ligament
• Inside is also the Palmar cutaneous branch of ulnar nerve, as well as superfical and deep branches and all the same nerves and arteries just specified relating to the ulnar