Wrist Instability

Introduction

Wrist instability is a complex clinical condition resulting from disruption of the normal anatomical and biomechanical relationships between the carpal bones. It may present following acute trauma or develop gradually due to degenerative or inflammatory processes. Accurate classification, thorough clinical examination, and appropriate imaging are essential for diagnosis and management. This article provides a structured overview of wrist instability, including terminology, examination principles, common diagnostic patterns, and evidence-based management strategies.

Orthopaedic Terminology

Understanding wrist instability requires familiarity with key orthopaedic definitions:

• DISI Deformity (Dorsal Intercalated Segment Instability): An increase in the scapholunate angle on lateral wrist radiographs (>60°), typically associated with scapholunate ligament injury or carpal fracture.

• VISI Deformity (Volar Intercalated Segment Instability): A reduction in the scapholunate angle (<30°), suggestive of lunotriquetral ligament injury.

• Proximal Carpal Row: Comprised of the scaphoid, lunate, triquetrum, and pisiform.

• Distal Carpal Row: Comprised of the trapezium, trapezoid, capitate, and hamate.

• Dissociative Carpal Instability: Instability between bones within the same carpal row.

• Nondissociative Carpal Instability: Instability occurring between carpal rows or between the distal radius and proximal row.

• Combined Carpal Instability: Coexistence of dissociative and nondissociative instability.

• Adaptive Carpal Instability: Gradual instability due to skeletal malalignment, such as distal radius malunion.

• Dynamic Carpal Instability: Instability evident only under load.

• Ulnar Translation: Progressive ulnar migration of the lunate, a form of nondissociative instability.

• Malunion: Healing of a fracture in a non-anatomical position.

Clinical Examination of Wrist Instability

Inspection

• Assess posture and alignment of both wrists and hands

• Look for deformity, swelling, or signs of inflammatory arthritis

• Ask the patient to demonstrate provocative movements or mechanical symptoms such as clunking

Palpation

A systematic palpation of the wrist should include:

• Dorsal and volar joint lines

• Midcarpal region

• Ulnar styloid and distal radioulnar joint

• Ulnar fovea (tenderness may indicate TFCC injury)

Significant tenderness may suggest advanced degenerative change or inflammatory pathology. The elbow and forearm should also be examined to exclude associated longitudinal instability.

Movement

• Estimate wrist flexion and extension

• Compare radial and ulnar deviation with the contralateral side

Normal Wrist Range of Motion

• Extension: 60°

• Flexion: 60°

• Ulnar deviation: 30°

• Radial deviation: 20°

Special Tests

• Functional assessment including reach and grip patterns

• Evaluation of six grip types used in daily activities

• Kirk–Watson Test for dynamic scapholunate instability
  A palpable or audible clunk during manoeuvre suggests scapholunate ligament injury.

Common Diagnoses in Wrist Instability

Dissociative Carpal Instability

Scapholunate Ligament Injury

Summary
Scapholunate ligament rupture is the most common cause of dissociative carpal instability. The proximal carpal row functions as an intercalated segment, and disruption of ligamentous continuity leads to predictable deformity patterns. Injury between the scaphoid and lunate results in scaphoid flexion and lunate extension, producing a DISI deformity. Lunotriquetral disruption leads to VISI deformity.

Presentation

• Acute or chronic onset

• Dorsal and radial-sided wrist pain

• Stiffness, crepitus, or pain with loading activities

Investigation

• PA and lateral wrist radiographs

• Assessment of Gilula’s lines

• Clenched fist views for dynamic widening

• MRI for definitive diagnosis in specialist care

Management

• Acute injuries require urgent referral

• Conservative management for stable or degenerative cases

• Surgery considered for displaced, unstable, or refractory cases

Lunotriquetral Ligament Injury

Summary
Lunotriquetral injuries are significantly less common than scapholunate injuries and typically present with ulnar-sided wrist pain.

Key Features

• Pain worsened with loading and pronation

• Possible wrist effusion

• Positive ballotment test

Imaging

• PA and lateral radiographs

• VISI deformity on lateral view

• MRI for confirmation

Management principles mirror those of scapholunate instability and are tailored to acuity and symptom severity.

Nondissociative Carpal Instability

Summary
Nondissociative carpal instability involves abnormal motion between carpal rows or between the radius and proximal row. It is rare in isolation and often associated with combined instability or inflammatory arthropathy.

Clinical Features

• Global wrist pain

• Reduced grip strength

• Stiffness and painful range of motion

Investigation

• PA and lateral radiographs

• Assessment for ulnar translation

• CT imaging in acute traumatic cases

Management

• Conservative treatment in low-symptom inflammatory cases

• Acute traumatic instability requires urgent surgical referral

Adaptive Carpal Instability

Summary
Adaptive carpal instability arises secondary to skeletal malalignment, most commonly distal radius malunion. Altered wrist biomechanics lead to progressive ligament attenuation and degenerative change.

Presentation

• History of previous distal radius fracture

• Progressive functional limitation

• Associated conditions such as carpal tunnel syndrome may be present

Imaging

• PA and lateral radiographs

• Measurement of radial height, inclination, and volar tilt

Management

• Conservative treatment for minimal symptoms

• Corrective osteotomy in selected cases

• Wrist fusion considered in advanced arthritis

Management Principles and Referral

Management of wrist instability is individualised and depends on:

• Acute versus chronic presentation

• Degree of instability

• Functional demands of the patient

• Presence of degenerative or inflammatory disease

Indications for Referral

• Acute high-energy wrist injuries

• Persistent pain and mechanical instability

• Failure of conservative management

Treatment Algorithms

Prognosis and Patient Expectations

The prognosis of wrist instability is multifactorial. Early diagnosis and appropriate management improve outcomes, while delayed or untreated instability may progress to degenerative wrist arthritis. Clear communication regarding treatment goals and realistic expectations is essential.