The human wrist is a complex structure, susceptible to various injuries and degenerative conditions. Scapholunate Advanced Collapse, commonly known as SLAC wrist, is a significant cause of chronic wrist pain and progressive arthritis. This article explains its origins, signs, diagnosis, and treatment options.
Understanding SLAC Wrist
SLAC wrist, or Scapholunate Advanced Collapse, is a degenerative arthritis in the wrist. It typically arises from long-standing instability or injury to the scapholunate ligament. This ligament primarily stabilizes the scaphoid and lunate bones, two of the eight small carpal bones in the wrist’s proximal row.
When the scapholunate ligament is damaged, often from trauma like a fall onto an outstretched hand, the normal alignment and motion between these bones are disrupted. The scaphoid bone may abnormally flex, and the lunate may extend, leading to an irregular distribution of forces across the wrist joints. This altered biomechanics causes the cartilage surfaces to wear down prematurely, initiating progressive degenerative arthritis. The collapse primarily affects the radiocarpal and midcarpal joints, leading to pain and dysfunction.
Recognizing the Signs
Individuals developing SLAC wrist often experience a range of symptoms that worsen over time as the condition progresses. Chronic wrist pain, frequently localized on the thumb side of the wrist, is a common symptom. This pain can intensify with heavy use or weight-bearing activities, and may be a dull ache or sharp, shooting pain with specific movements.
Patients may also notice increasing stiffness in the wrist, leading to a reduced range of motion, particularly affecting the ability to extend the wrist or move it towards the thumb side (radial deviation). A grinding, clicking, or popping sensation during wrist movement is often reported, indicating the friction of degenerating joint surfaces. A decrease in grip strength and difficulty performing tasks that require wrist stability, such as using hand tools or lifting objects, are common complaints. These symptoms often develop gradually, sometimes many years after the initial ligament injury.
Identifying the Condition
Diagnosing SLAC wrist typically begins with a thorough physical examination. A medical professional assesses the wrist’s range of motion, stability, and identifies areas of tenderness, often directly over the scapholunate ligament. Specific provocative tests, such as the Watson scaphoid shift test, may be performed to evaluate scapholunate instability.
Imaging studies are crucial for confirming a SLAC wrist diagnosis and determining its severity. X-rays are the primary imaging tool, revealing characteristic changes like a widening gap between the scaphoid and lunate bones, abnormal scaphoid flexion, carpal collapse, and narrowing of joint spaces due to cartilage loss. While X-rays show bone changes and arthritis, they do not directly visualize soft tissue damage like ligament tears. For a more detailed assessment of soft tissues or to evaluate bone structure and degeneration, magnetic resonance imaging (MRI) or computed tomography (CT) scans may be utilized.
Treatment Approaches
Managing SLAC wrist involves a range of strategies, tailored to the condition’s stage and individual needs. Non-surgical approaches are often the first line of treatment, particularly in earlier stages or for symptom management. These may include modifying activities to reduce stress on the wrist, using pain relief medications such as nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce pain and inflammation, and wearing splints or braces to immobilize the wrist and provide support. Physical therapy is beneficial, focusing on exercises to maintain or improve wrist range of motion and strength. Corticosteroid injections can also provide temporary pain relief by reducing inflammation within the joint.
When conservative treatments no longer provide adequate relief, surgical interventions become an option. The goals of surgery include alleviating pain and improving wrist function. Several surgical procedures exist, and the choice depends on the extent of arthritis and patient-specific factors.
Partial wrist fusions, such as a four-corner fusion (scaphoidectomy and fusion of four other carpal bones), aim to stabilize the wrist and reduce pain while preserving some motion. Proximal row carpectomy (PRC) involves removing the scaphoid, lunate, and triquetrum bones to create a new, pain-free joint surface. For severely damaged joints, wrist arthroplasty, or total wrist replacement, involves replacing the arthritic joint surfaces with an artificial implant. Total wrist fusion, where all wrist bones are fused into a single solid bone, eliminates motion but can provide significant pain relief in very advanced cases.