Carpal instability

Page 1 …….. Introduction
Page 2 …….. Classification
Page 3 …….. Scapholunate Dissociation
Page 4 …….. Luno-triquetral Dissociation
Page 5 …….. Uncommon Patterns

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Definition

Carpal instability refers to malalignment of carpal bones due to injury or disease, disrupting the normal biomechanics and stability of the wrist.

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Anatomy

Carpal Bones

• Proximal Row: Scaphoid, Lunate, Triquetrum, Pisiform (intercalated segment).
• Distal Row: Trapezium, Trapezoid, Capitate, Hamate.

Carpal Columns

1. Lateral (Mobile) Column: Scaphoid, Trapezium, Trapezoid.
2. Central (Flexion-Extension) Column: Lunate, Capitate, Hamate.
3. Medial (Rotation) Column: Triquetrum, Pisiform, Hamate.

Carpal Ligaments  Mcq ❓️

1. Intrinsic Ligaments (connect carpal bones within rows):
   • Scapholunate, Lunotriquetral, Scaphocapitate, Trapeziocapitate.
2. Extrinsic Ligaments (connect carpal bones to radius or metacarpals):
   • Volar radiocarpal, Volar ulnocarpal, Dorsal radiocarpal, Radial collateral, Ulnotriquetral, Radiotriquetral, Radioscapholunate.

Notable Feature:

• Space of Poirier: A central weak area on the palmar aspect of the capitolunate space, prone to instability. Mcq ❓️

Three carpal arcs (Gilula arcs), which are shown as pink (arc I), blue (arc II), and red (arc III)

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Role of the Lunate

• Lunate is central (key stone or arc stone) to carpal stability, connecting to the scaphoid and triquetrum via ligaments.
• Injuries:
  • Scapholunate injury → Dorsal intercalated segment instability (DISI).
  • Lunotriquetral injury → Volar intercalated segment instability (VISI).

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