DRUJ Instabilities & Dislocations

The distal radioulnar joint (DRUJ) is a pivotal articulation between the distal ends of the radius and ulna, essential for forearm rotation and wrist stability. Instability or dislocation of the DRUJ can significantly impair wrist function and is often classified based on the direction of displacement: dorsal, volar, or multidirectional.

Anatomy and Biomechanics:

The DRUJ is stabilized by several key structures: the triangular fibrocartilage complex (TFCC), the dorsal and volar radioulnar ligaments, the interosseous membrane, and the joint capsule. The TFCC acts as the primary stabilizer, cushioning and maintaining congruity between the radius and ulna during pronation and supination.

Types of Instability and Dislocation:

Dorsal Dislocation: The distal ulna displaces dorsally relative to the radius, often occurring with forced pronation injuries.
Volar Dislocation: The ulna moves volarly, typically due to forced supination.
Multidirectional Instability: Involves laxity or injury to multiple stabilizing structures, leading to instability in more than one direction.

Causes and Associated Injuries:

DRUJ instability can result from acute trauma such as falls, fractures (notably distal radius fractures and Galeazzi fracture-dislocations), or ligamentous injuries. Chronic instability may develop from repetitive stress or untreated acute injuries. Galeazzi fractures, characterized by a radial shaft fracture with DRUJ dislocation, are a classic example requiring surgical stabilization.

Clinical Presentation:

Patients often report wrist pain, a feeling of looseness or clicking during forearm rotation, and decreased grip strength. Physical examination may reveal tenderness over the DRUJ, abnormal mobility of the ulna, and positive provocative tests like the piano key sign.

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Diagnosis:

Radiographic evaluation includes standard wrist X-rays, with special views to assess DRUJ alignment. CT scans provide detailed assessment of joint congruity and subtle subluxations. MRI is valuable for evaluating soft tissue injuries, especially the TFCC.

Treatment:

Acute Dislocations: Closed reduction followed by immobilization in a long-arm cast or splint for 4-6 weeks is typical.
Chronic Instability: May require surgical intervention such as TFCC repair, ulnar shortening osteotomy, or DRUJ stabilization procedures.
Associated Fractures: Surgical fixation of fractures and stabilization of the DRUJ are often necessary.

Rehabilitation:

Post-immobilization, hand therapy focuses on restoring range of motion, strengthening the forearm muscles, and improving proprioception to prevent recurrence.

Understanding the complex anatomy and biomechanics of the DRUJ is crucial for accurate diagnosis and effective management of its instabilities and dislocations, ensuring optimal functional recovery.

Anatomy and Biomechanics

The DRUJ is formed by the articulation between the sigmoid notch of the distal radius and the ulnar head.
The sigmoid notch has a larger radius of curvature than the ulnar head, resulting in inherent laxity and minimal bony constraint.
Only about 10% of the articular surface is in contact, with the joint geometry contributing approximately 20% of stability.
The remaining 80% of stability is provided by soft tissues, primarily the triangular fibrocartilage complex (TFCC).
The TFCC includes the volar and dorsal radioulnar ligaments, which have superficial and deep fibers attaching to the ulnar fovea and styloid.
Dynamic stabilizers include the extensor carpi ulnaris (ECU) tendon and pronator quadratus muscle.
The distal interosseous membrane (DIOM), especially the distal oblique ligament (DOL), also plays a key role in static stability.
The TFCC transmits about 16% of axial load between the carpus and forearm and is vascularized peripherally but avascular centrally.

Types and Causes of DRUJ Instability

Types of Instability:

Dorsal Instability: Ulnar head subluxates or dislocates dorsally, often seen in forced pronation injuries.
Volar Instability: Ulnar head moves volarly, typically due to forced supination.
Multidirectional Instability: Laxity in multiple directions due to combined ligamentous injuries or generalized ligamentous laxity.

Common Causes:

Acute trauma such as falls on an outstretched hand or rotational injuries.
Fractures involving the distal radius, especially those affecting the sigmoid notch or lunate facet.
Galeazzi fractures (radial shaft fracture with DRUJ dislocation).
Essex-Lopresti lesions involving interosseous membrane disruption.
TFCC tears, especially at the foveal insertion.
Malunions of distal radius fractures altering joint congruity.
Generalized ligamentous laxity or inflammatory arthritis.

Clinical Presentation and Examination

Patients typically present with ulnar-sided wrist pain, weakness, and a sensation of instability or clunking during forearm rotation.
Key Physical Tests:
Piano Key Sign: Pressing the ulnar head causes it to depress and rebound, indicating dorsal instability.
Grind Test: Pro-supination with ulnar deviation reproduces pain by grinding the carpus over the TFCC.
Fovea Sign: Tenderness over the ulnar fovea between the styloid and FCU tendon.
Ballottement (DRUJ Stress) Test: Shucking the ulna against the radius to assess translation and pain.
Press Test:Patient pushes up from a chair using hands, provoking ulnar-sided pain if TFCC is injured.

Imaging and Diagnostic Modalities

Radiographs: Standard and specialized views (e.g., dorsal tangential) to assess alignment and detect fractures or subluxations.
Computed Tomography (CT): Bilateral CT scans in neutral, pronation, and supination to evaluate joint congruity and subtle instability.
- Methods include Mino technique, congruency method, epicenter method (most specific), and ratio method.
Magnetic Resonance Imaging (MRI): High-resolution 3T MRI to assess soft tissue injuries, especially TFCC tears.
Arthroscopy: Gold standard for direct visualization and treatment of TFCC and other ligamentous injuries.
Ultrasound: Emerging tool for dynamic assessment of DRUJ laxity during provocative maneuvers.
Forearm Torque Measurement: Dynamometry to quantify pronation and supination strength deficits.

Treatment Strategies

Acute DRUJ Instability:
- Closed reduction under anesthesia.
- Immobilization in the position of stability (supination for dorsal dislocation, pronation for volar dislocation) for 4-6 weeks.
- Surgical repair of TFCC if instability persists after reduction.
Chronic Instability:
- Nonoperative treatment may be attempted in mild cases with low functional demands.
- Corrective osteotomy for distal radius malunion to restore bony alignment.
- TFCC repair or reconstruction, especially for peripheral tears with good tissue quality.
- Ulnar shortening osteotomy for ulnar impaction syndrome.
- Sigmoid notchplasty may be performed to deepen a flat sigmoid notch and improve stability.
- Ligament reconstruction techniques (open or arthroscopic) using tendon grafts (e.g., Adams procedure) to restore radioulnar ligament function.
- Arthroscopic thermal stabilization for mild to moderate chronic instability.
Salvage Procedures:
- Darrach procedure (distal ulnar resection) for severe cases but may cause instability of the ulnar stump.
- Sauvé-Kapandji arthrodesis combining DRUJ fusion with a proximal ulnar pseudoarthrosis.
- Prosthetic replacement (hemiarthroplasty or total DRUJ arthroplasty) for painful, unstable, and arthritic joints.

Conclution

DRUJ instability and dislocations are complex conditions involving bony and soft tissue structures. Accurate diagnosis requires thorough clinical examination supported by advanced imaging. Treatment ranges from conservative management to complex reconstructive surgeries, with the goal of restoring joint stability, relieving pain, and preserving forearm rotation and grip strength. Understanding the intricate anatomy and biomechanics of the DRUJ is essential for optimal patient outcomes.

Distal radioulnar joint (DRUJ) instabilities and dislocations represent challenging clinical conditions due to the joint’s complex anatomy and reliance on both bony congruity and soft tissue stabilizers, particularly the triangular fibrocartilage complex (TFCC). Accurate diagnosis through careful clinical evaluation and advanced imaging is essential to identify the type and extent of instability. Early and appropriate management—ranging from conservative immobilization in acute cases to surgical repair or reconstruction in chronic or complex injuries—is critical to restore joint stability, preserve forearm rotation, and maintain wrist function. A comprehensive understanding of DRUJ biomechanics and pathology enables tailored treatment strategies that optimize functional outcomes and minimize long-term complications such as chronic pain and osteoarthritis.

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