Distal Radius Ligament Injuries: SLL, TFCC, Causes, Symptoms, and Treatment

What ligament is injured in the distal radius?

The most frequently injured ligament in the distal radius region, often in conjunction with distal radius fractures, is the scapholunate ligament (SLL), though the triangular fibrocartilage complex (TFCC) is also highly susceptible to injury, particularly on the ulnar side of the wrist.

Understanding the Distal Radius and Wrist Anatomy

The distal radius, the wider end of the forearm bone closest to the hand, forms a critical part of the wrist joint. This region articulates with the carpal bones (scaphoid and lunate) to facilitate a complex array of movements including flexion, extension, radial deviation, and ulnar deviation. The stability and intricate mechanics of the wrist are not solely dependent on the bones, but crucially on a network of strong, fibrous ligaments that connect these bones, providing both stability and guided motion. Injuries to the distal radius, particularly fractures, often involve concomitant damage to these vital soft tissue structures, which can significantly impact long-term wrist function.

The Primary Suspects: Ligaments of the Distal Radius

While various ligaments contribute to wrist stability, two complexes are overwhelmingly implicated in injuries associated with the distal radius:

The Scapholunate Ligament (SLL)

The scapholunate ligament (SLL) is an intrinsic, C-shaped ligament that connects the scaphoid and lunate carpal bones. It is perhaps the most critical ligament for maintaining carpal stability and alignment.

• Function: The SLL is essential for coordinating the movement of the scaphoid and lunate, which in turn influences the kinematic chain of the entire wrist. It prevents these two bones from separating or rotating abnormally.
• Mechanism of Injury: Tears of the SLL are most commonly caused by a fall on an outstretched hand (FOOSH) with the wrist in hyperextension and ulnar deviation. This mechanism is also the most common cause of distal radius fractures, explaining the high co-occurrence of SLL injuries with these fractures. High-energy trauma can lead to complete dissociation.
• Consequences of Injury: An injured SLL can lead to scapholunate instability, where the scaphoid and lunate move independently. Over time, this abnormal motion can cause progressive wrist arthritis, known as ScaphoLunate Advanced Collapse (SLAC) wrist, characterized by chronic pain, stiffness, and weakness.

The Triangular Fibrocartilage Complex (TFCC)

The triangular fibrocartilage complex (TFCC) is a complex structure located on the ulnar side of the wrist, acting as a critical stabilizer and cushion. It comprises an articular disc, meniscal homolog, dorsal and volar radioulnar ligaments, and ulnocarpal ligaments.

• Function: The TFCC has multiple roles:
  • It stabilizes the distal radioulnar joint (DRUJ), which allows forearm rotation (pronation and supination).
  • It acts as a primary load-bearing structure, transmitting compressive forces from the hand to the forearm, particularly across the ulnar side of the wrist.
  • It cushions the ulnar carpal bones.
  • It provides a smooth articular surface for the carpus.
• Mechanism of Injury: TFCC injuries can be acute or degenerative.
  • Acute tears often result from a FOOSH injury with the forearm pronated or supinated, or from a sudden, forceful rotation and axial loading of the wrist (e.g., using a drill, sports activities). Distal radius fractures, especially those involving the ulnar side or with significant displacement, frequently involve concomitant TFCC tears.
  • Degenerative tears are common with age and repetitive stress, particularly in individuals with positive ulnar variance (where the ulna is longer than the radius).
• Consequences of Injury: TFCC tears can cause ulnar-sided wrist pain, clicking, catching, weakness, and instability of the DRUJ, significantly impacting grip strength and rotational movements of the forearm.

Other Relevant Ligaments

While less commonly the primary ligament injured in direct association with a distal radius fracture, other ligaments play crucial roles in overall wrist stability and can be involved in complex trauma:

• Radioscaphocapitate Ligament (RSL): A strong volar (palm-side) extrinsic ligament that connects the radius to the scaphoid and capitate, important for carpal stability.
• Lunotriquetral Ligament (LTL): An intrinsic ligament connecting the lunate and triquetrum. While less frequently injured with distal radius fractures than the SLL, its injury can also lead to carpal instability.

Mechanisms of Injury Associated with Distal Radius Trauma

The most prevalent mechanism for both distal radius fractures and associated ligamentous injuries is a fall on an outstretched hand (FOOSH). The precise position of the wrist at impact (e.g., degree of hyperextension, ulnar or radial deviation, forearm rotation) dictates which specific bones fracture and which ligaments are most susceptible to tearing. High-energy trauma, such as sports injuries or motor vehicle accidents, can also lead to complex wrist injuries involving multiple bone and ligamentous structures.

Clinical Presentation and Diagnosis

Patients with distal radius fractures and concomitant ligamentous injuries will typically present with:

• Pain: Often localized over the fracture site but potentially radiating to the specific ligament injured (e.g., dorsal wrist pain for SLL, ulnar-sided pain for TFCC).
• Swelling and Bruising: Common with fractures and soft tissue damage.
• Decreased Range of Motion: Especially with rotational movements (pronation/supination) if the TFCC is involved, or with flexion/extension if carpal stability is compromised.
• Instability, Clicking, or Catching: Particularly indicative of ligamentous disruption.
• Weakness: Especially in grip strength.

Diagnosis involves a multi-modal approach:

• Clinical Examination: Palpation, range of motion assessment, and specific provocative tests (e.g., Watson scaphoid shift test for SLL, fovea sign for TFCC).
• X-rays: Essential for diagnosing fractures and can sometimes show indirect signs of ligamentous injury, such as a widened scapholunate gap ("Terry Thomas sign") or carpal malalignment.
• Magnetic Resonance Imaging (MRI): The gold standard for visualizing soft tissue injuries like ligament tears and TFCC damage.
• Computed Tomography (CT) Scan: Useful for detailed bone assessment, particularly for complex fractures and evaluating the DRUJ.
• Wrist Arthroscopy: Often considered the definitive diagnostic tool, allowing direct visualization of the ligaments and cartilage, and often enabling simultaneous repair.

Management and Rehabilitation Principles

Management of distal radius fractures with associated ligamentous injuries aims to restore anatomical alignment, stability, and function.

• Acute Phase: Initial management involves immobilization (casting or splinting), pain control (NSAIDs), and the RICE protocol (Rest, Ice, Compression, Elevation).
• Conservative Management: For less severe ligamentous injuries, conservative treatment may involve prolonged immobilization, followed by a structured physical therapy program focusing on regaining range of motion, strengthening intrinsic and extrinsic wrist musculature, and proprioceptive training.
• Surgical Intervention: Many significant ligamentous injuries, especially complete SLL tears or unstable TFCC tears, require surgical repair or reconstruction to prevent chronic instability and progressive arthritis. The specific surgical approach depends on the ligament involved, the severity of the tear, and the presence of associated fractures.
• Rehabilitation: Post-surgical or post-immobilization rehabilitation is crucial. It progresses through phases:
  • Early Mobilization: Gentle range of motion exercises.
  • Strengthening: Gradual progression of exercises targeting wrist flexors, extensors, pronators, supinators, and grip strength.
  • Proprioception and Stability Training: Exercises to improve joint awareness and dynamic stability.
  • Return to Activity: Sport-specific or occupation-specific training to safely return to pre-injury activity levels.

Importance of Early and Accurate Diagnosis

Given the potential for long-term complications such as chronic pain, instability, and debilitating arthritis, early and accurate diagnosis of ligamentous injuries accompanying distal radius trauma is paramount. Overlooking these soft tissue injuries can lead to persistent symptoms and necessitate more complex interventions later. A thorough evaluation by a hand or wrist specialist is essential to ensure a comprehensive diagnosis and optimal treatment plan, facilitating the best possible functional outcome.