Carpal Instability – High-Yield Orthopedic Notes

Introduction

• Carpal instability is an important cause of chronic wrist pain and dysfunction
• Frequently tested in:
  • Viva examinations
  • MCQs
  • Clinical case discussions
• Requires understanding of:
  • Wrist anatomy
  • Ligament biomechanics
  • Radiological patterns
  • Management principles

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Basic Anatomy & Biomechanics

Wrist Ligaments

Extrinsic Ligaments

Connect:

• Radius to carpus
• Ulna to carpus

Functions:

• Global wrist stability
• Maintain carpal alignment

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Intrinsic Ligaments

Connect carpal bones to each other.

Important ligaments:

• Scapholunate ligament
• Lunotriquetral ligament

Functions:

• Maintain intercarpal alignment
• Control carpal motion

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Important Anatomical Concepts

• Carpus has:
  • Proximal row
  • Distal row
  • Three columns

Important structures:

• Scaphoid bridges proximal and distal rows
• Lunate is central to carpal stability
• Lunocapitate joint is center of rotation

Load transmission:

• Radial column bears ~75% load
• Ulnar column bears ~25% load

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Carpal Kinematics

During radial deviation:

• Scaphoid flexes
• Lunate flexes with scaphoid

During ulnar deviation:

• Scaphoid extends
• Lunate dorsiflexes

Normal motion requires intact ligament support.

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Definition of Carpal Instability

Inability of the wrist to maintain normal alignment during physiological loading.

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Classification of Carpal Instability

1. Dissociative Instability

Occurs within the same carpal row.

Examples:

• Scapholunate dissociation
• Lunotriquetral dissociation

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2. Non-dissociative Instability

Occurs between carpal rows.

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3. Complex Instability

Involves both rows and columns.

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4. Adaptive Instability

Secondary to:

• Distal radius malunion
• Scarring
• Previous surgery
• Altered ligament length

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Dynamic vs Static Instability

Dynamic

Seen only during stress/loading:

• Clenched fist view
• Radial/ulnar deviation

Usually early injury.

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Static

Visible on resting X-rays.

Suggests:

• Chronic injury
• Severe instability

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Clinical Features

Acute Injury

• Pain
• Swelling
• Reduced wrist movement
• Deformity
• Possible neuropathy

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Chronic Injury

• Weakness
• Persistent pain
• Clicking sensation
• Feeling that wrist “slips”

Common diagnostic error:

• Mistaken as simple wrist sprain

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Investigations

Plain Radiographs

Essential views:

• AP
• Lateral
• Oblique
• Clenched fist view
• Radial/ulnar deviation views

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MRI

Useful in acute ligament injuries.

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MR Arthrogram

Better for chronic injuries and TFCC tears.

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Arthroscopy

Gold standard for diagnosis.

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Important Wrist Angles

Scapholunate Angle (Most Important)

Normal:

• 30°–60°

Interpretation:

• <30° = VISI

• 70° = DISI

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DISI (Dorsal Intercalated Segment Instability)

Cause

Usually due to:

• Scapholunate ligament injury

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X-ray Findings

AP View

• Increased scapholunate gap
• Terry Thomas sign (>3 mm gap)
• Cortical ring sign
• Shortened scaphoid appearance

Lateral View

• Scapholunate angle >70°
• Dorsally tilted lunate

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Scapholunate Ligament Anatomy

• C-shaped ligament between scaphoid and lunate

Important part:

• Dorsal component:
  • Thickest
  • Strongest
  • Main stabilizer

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Management of Scapholunate Injury

Partial Acute Injury

• Arthroscopy
• Debridement
• Temporary K-wire fixation
• Immobilization

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Acute Complete Injury

• Primary repair preferred
• Dorsal approach commonly used
• Ligament repair + K-wire protection
• Cast ~8 weeks

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Chronic Reducible Injury

• Ligament reconstruction

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Chronic Irreducible/Degenerative Injury

• Fusion
• Salvage procedure

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Scapholunate Reconstruction Procedures

Brunelli Procedure

Uses:

• Flexor carpi radialis tendon strip

Technique:

• Tendon passed through scaphoid tunnel

Other techniques:

• Garcia-Elias
• Capsulodesis
• Retinacular grafts

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Geissler Classification

Arthroscopic grading system for scapholunate injury.

General concept:

• Low-grade injuries:
  • Conservative/simple stabilization
• High-grade injuries:
  • Repair/reconstruction

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SLAC Wrist (Scapholunate Advanced Collapse)

Definition

Degenerative arthritis due to untreated scapholunate instability.

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Stages

Stage 1

• Radial styloid-scaphoid arthritis

Stage 2

• Entire scaphoid fossa involved

Stage 3

• Capitolunate arthritis

Stage 4

• Pancarpal arthritis

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Management of SLAC Wrist

Stage 1

• Radial styloidectomy

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Stage 2 & 3

• Scaphoid excision
• Four-corner fusion

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Low-demand patient

• Proximal row carpectomy

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Heavy laborer

• Total wrist arthrodesis

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Pain-relief Option

• Wrist denervation/neurectomy

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VISI (Volar Intercalated Segment Instability)

Cause

Usually due to:

• Lunotriquetral ligament injury

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Radiological Findings

• Scapholunate angle <30°
• Volarly tilted lunate
• Negative radiolunate angle

Associated injuries:

• TFCC injury
• Ulnocarpal ligament injury

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Management of VISI

Acute Injury

Preferred treatment:

• Arthroscopy
• Debridement
• Repair if tissue quality adequate

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Chronic Cases

• Reconstruction difficult
• Less predictable results
• Salvage/fusion may be needed

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Perilunate Injuries

Importance

• Commonly missed injury
• AP view may appear normal
• Lateral view is critical

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Mechanism

• Forceful wrist extension + ulnar deviation

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Mayfield Progression

Injury progresses radial to ulnar.

Stages

Stage 1

• Scapholunate injury/scaphoid fracture

Stage 2

• Capitolunate involvement

Stage 3

• Lunotriquetral injury/triquetral fracture

Stage 4

• Lunate dislocation

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Lesser Arc vs Greater Arc Injury

Lesser Arc

• Pure ligament injury

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Greater Arc

Injury through bones:

• Scaphoid
• Capitate
• Triquetrum
• Radial styloid

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Gilula’s Carpal Arcs

Three smooth arcs should be maintained on AP X-ray.

Break in arc suggests:

• Carpal instability
• Dislocation

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Management of Perilunate Injury

Initial

• Closed reduction may temporarily relieve:
  • Median nerve compression
  • Acute deformity

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Definitive Treatment

• Repair fractures and ligaments
• Best treated within 6 weeks

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Chronic Neglected Cases

May require:

• Proximal row carpectomy
• Wrist arthrodesis
• Salvage procedures

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Wrist Denervation

Purpose:

• Pain relief in chronic wrist conditions

Does NOT correct deformity.

Benefits:

• Temporary symptom relief
• Preserves wrist motion

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High-Yield Exam Pearls

• DISI:
  • Scapholunate ligament injury
  • SL angle >70°
  • Lunate tilted dorsally
• VISI:
  • Lunotriquetral ligament injury
  • SL angle <30°
  • Lunate tilted volarly
• Terry Thomas sign:
  • SL gap >3 mm
• Arthroscopy = gold standard investigation
• Always request lateral X-ray in suspected perilunate injury
• Untreated SL instability leads to SLAC wrist