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Updated: Mar 7 2024

# Wrist Ligaments & Biomechanics

Images
• Wrist Planes of Motion
• Joints involved
• intercarpal
• Three axes of motion
• flexion-extension
• prono-supination
• Normal and function motion
• flexion (65 normal, 10 functional)
• 40% radiocarpal, 60% midcarpal
• extension (55 normal, 35 functional)
• 66% radiocarpal, 33% midcarpal
• radial deviation (15 normal, 10 functional)
• 90% midcarpal
• ulnar deviation (35 normal, 15 functional)
• 50% radiocarpal, 50% midcarpal
• Wrist Biomechanics
• Three biomechanic concepts have been proposed:
• three links in a chain composed of radius, lunate and capitate
• head of capitate acts as center of rotation
• proximal row (lunate) acts as a unit and is an intercalated segment with no direct tendon attachments
• distal row functions as unit
• efficient motion (less motion at each link)
• strong volar ligaments enhance stability
• more links increases instability of the chain
• scaphoid bridges both carpal rows
• resting forces/radial deviation push the scaphoid into flexion and push the triquetrum into extension
• ulnar deviation pushes the scaphoid into extension
• Column concept
• lateral (mobile) column
• comprises scaphoid, trapezoid and trapezium
• scaphoid is center of motion and function is mobile
• central (flexion-extension) column
• comprises lunate, capitate and hamate
• luno-capitate articulation is center of motion
• motion is flexion/extension
• medial (rotation) column
• comprises triquetrum and distal carpal row
• motion is rotation
• Rows concept
• comprises proximal and distal rows
• scaphoid is a bridge between rows
• motion occurs within and between rows
• Carpal Relationships
• Carpal collapse
• normal ratio of carpal height to 3rd metacarpal height is 0.54
• Ulnar translation
• normal ratio of ulna-to-capitate length to 3rd metacarpal height is 0.30
• distal radius bears 80% of load
• distal ulna bears 20% of load
• ulna load bearing increases with ulnar lengthening
• ulna load bearing decreases with ulnar shortening
• Wrist Ligaments
• The ligaments of the wrist include
• extrinsic ligaments
• bridge carpal bones to the radius or metacarpals
• include volar and dorsal ligaments
• intrinsic ligaments
• originate and insert on carpal bones
• the most important intrinsic ligaments are the scapholunate interosseous ligament and lunotriquetral interosseous ligament
• Characteristics
• volar ligaments are secondary stabilizers of the scaphoid
• volar ligaments are stronger than dorsal ligaments
• dorsal ligaments converge on the triquetrum
• Space of Poirier
• center of a double "V" shape convergence of ligaments
• central weak area of the wrist in the floor of the carpal tunnel at the level of the proximal capitate
• between the volar radioscaphocapitate ligament and volar long radiolunate ligament (radiolunotriquetral ligament)
• wrist palmar flexion
• area of weakness disappears
• wrist dorsiflexion
• area of weakness increases
• in perilunate dislocations, this space allows the distal carpal row to separate from the lunate
• in lunate dislocations, the lunate escapes into this space
• Extrinsic Ligaments
• Volar radiocarpal ligaments
• at risk for injury with excessively large radial styloid
• from radial styloid to capitate, creating a sling to support the waist of the scaphoid
• preserve when doing proximal row carpectomy
• acts as primary stabilizer of the wrist after PRC and prevents ulnar drift
• also called radiolunotriquetral or volar radiolunate ligament
• counteracts ulnar-distal translocation of the lunate
• abnormal in Madelung's deformity
• referred to as Vickers ligament
• Ligament of Testut and Kuentz
• only functions as neurovascular conduit
• not a true ligament
• does not add mechanical strength
• stabilizes lunate
• Volar ulnocarpal ligaments
• ulnotriquetral
• ulnolunate
• ulnocapitate
• Dorsal ligaments
• also referred to as dorsal radiocarpal ligament (DRC)
• must also be disrupted for VISI deformity to form (in combination with rupture of lunotriquetral interosseous ligament rupture)
• dorsal intercarpal (DIC)
• Intrinsic (Interosseous) ligaments
• Proximal row
• scapholunate ligament
• primary stabilizer of scapholunate joint
• composed of 3 components
• dorsal portion
• thickest and strongest
• prevents translation
• volar portion
• prevents rotation
• proximal portion
• no significant strength
• disruption leads to lunate extension when the scaphoid flexes
• creating DISI deformity
• lunotriquetral ligament
• composed of 3 components
• dorsal
• volar
• strongest
• proximal
• disruption leads to lunate flexion when the scaphoid is normally aligned
• creating VISI deformity (in combination with rupture of dorsal radiotriquetral rupture)
• Distal row
• trapeziotrapezoid ligament
• trapeziocapitate ligament
• capitohamate ligament
• Palmar midcarpal
• scaphotrapeziotrapezoid
• scaphocapitate
• triquetralcapitate
• triquetralhamate
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