SLAC Wrist (Scapholunate Advanced Collapse)

SLAC Wrist, or Scapholunate Advanced Collapse, is a progressive and debilitating wrist condition that results from chronic instability of the scapholunate joint. It is one of the most common causes of wrist arthritis and pain, often leading to significant functional impairment. Understanding SLAC Wrist, its causes, symptoms, diagnosis, and treatment options is essential for patients and healthcare providers to manage this condition effectively and preserve wrist function.

Anatomy and Biomechanics of the Wrist

The wrist is a complex joint composed of eight small carpal bones arranged in two rows, connected by ligaments that provide stability and allow smooth motion. The scaphoid and lunate bones are two key bones in the proximal row that articulate closely and are stabilized by the scapholunate ligament.

The scapholunate ligament is critical for maintaining the normal alignment and coordinated movement between the scaphoid and lunate bones. When this ligament is injured or ruptured, it leads to abnormal motion and instability between these bones, setting the stage for SLAC Wrist.

What is SLAC Wrist?

SLAC Wrist is a pattern of wrist arthritis that develops secondary to chronic scapholunate ligament injury. When the scapholunate ligament is damaged, the scaphoid bone tends to flex forward (volarly), while the lunate bone extends backward (dorsally). This abnormal alignment causes uneven wear and tear on the cartilage surfaces of the wrist joint.

Over time, this leads to progressive degeneration and collapse of the wrist joint, particularly affecting the radioscaphoid and capitolunate joints. The condition is termed “advanced collapse” because it represents a late stage of untreated or inadequately treated scapholunate instability.

Causes and Risk Factors

The primary cause of SLAC Wrist is injury to the scapholunate ligament, which can occur due to:

Trauma: Falls on an outstretched hand, wrist sprains, or fractures can damage the ligament.
Repetitive stress: Activities involving repetitive wrist motions or heavy manual labor may contribute to ligament weakening.
Previous wrist injuries: Untreated or poorly managed scapholunate ligament tears increase the risk.
Degenerative changes: Age-related wear and tear can exacerbate ligament laxity and joint degeneration.
Inflammatory arthritis: Conditions like rheumatoid arthritis may accelerate joint damage.

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Symptoms of SLAC Wrist

Patients with SLAC Wrist typically experience:

Chronic wrist pain: Usually localized to the radial (thumb) side of the wrist, worsening with activity.
Stiffness and swelling: The wrist may feel stiff, swollen, and tender.
Decreased range of motion: Difficulty bending or extending the wrist fully.
Weakness: Reduced grip strength and difficulty performing daily tasks.
Clicking or popping: Sensation of instability or mechanical symptoms during wrist movement.
Progressive symptoms: Over time, pain and dysfunction worsen as arthritis advances.

Diagnosis

Diagnosing SLAC Wrist involves a thorough clinical evaluation and imaging studies:

Physical examination: The doctor assesses wrist tenderness, swelling, range of motion, and performs specific tests to evaluate scapholunate ligament integrity.
X-rays: Standard wrist X-rays reveal characteristic changes such as scapholunate dissociation (widening of the scapholunate gap), abnormal bone alignment, and joint space narrowing indicative of arthritis.
Stress views: Clenched fist or radial deviation views may better demonstrate instability.
MRI: Provides detailed images of soft tissues, including ligament tears and cartilage damage.
CT scan: Useful for assessing bone alignment and joint surfaces.
Arthroscopy: Minimally invasive procedure to directly visualize ligament damage and cartilage condition.

Stages of SLAC Wrist

SLAC Wrist progresses through distinct stages, which guide treatment decisions:

Stage I: Arthritis is limited to the radioscaphoid joint, with joint space narrowing and cartilage loss on the radial side.
Stage II: Arthritis progresses to involve the entire radioscaphoid joint.
Stage III: Arthritis extends to the capitolunate joint, while the radiolunate joint remains relatively preserved.
Stage IV: Advanced arthritis affects the entire wrist, including the radiolunate joint, leading to severe collapse and dysfunction.

Treatment Options

Treatment of SLAC Wrist depends on the stage of the disease, severity of symptoms, and patient activity level.

Non-Surgical Treatment

Immobilization: Wrist splints or braces can reduce pain and provide support.
Medications: NSAIDs and analgesics help control pain and inflammation.
Physical therapy: Exercises to maintain wrist mobility and strengthen surrounding muscles.
Injections: Corticosteroid injections may provide temporary relief.

Non-surgical treatment is generally reserved for early-stage SLAC Wrist or patients who are not candidates for surgery.

Surgical Treatment

Surgery is often necessary for advanced SLAC Wrist or when conservative measures fail. Surgical options include:

Radial styloidectomy: Removal of the radial styloid to relieve impingement and pain in early stages.
Partial wrist fusion (Four-corner fusion): Fusion of the capitate, lunate, hamate, and triquetrum bones to stabilize the wrist while preserving some motion.
Proximal row carpectomy: Removal of the proximal row of carpal bones (scaphoid, lunate, triquetrum) to reduce pain and maintain wrist motion.
Total wrist fusion (arthrodesis): Fusion of the entire wrist joint to eliminate pain but sacrifice motion, reserved for severe arthritis.
Wrist replacement (arthroplasty): In select cases, wrist joint replacement may be considered to preserve motion.

The choice of surgery depends on patient age, activity level, and extent of arthritis.

Rehabilitation and Recovery

Postoperative rehabilitation is critical for optimal recovery. It typically involves:

Immobilization in a cast or splint for several weeks.
Gradual introduction of range of motion exercises.
Strengthening exercises to restore function.
Regular follow-up to monitor healing and detect complications.

Recovery time varies depending on the procedure but generally ranges from 3 to 6 months.

Prognosis

With timely diagnosis and appropriate treatment, many patients with SLAC Wrist achieve significant pain relief and improved wrist function. Early-stage disease responds well to conservative or limited surgical interventions. Advanced stages may require more extensive surgery, which can restore stability but may limit wrist motion.

Untreated SLAC Wrist leads to progressive arthritis, chronic pain, and disability, underscoring the importance of early intervention.

Prevention and Patient Advice

While not all cases of SLAC Wrist can be prevented, certain measures can reduce risk and slow progression:

Protect the wrist: Use protective gear during sports or activities with high risk of wrist injury.
Avoid repetitive strain: Take breaks and use ergonomic tools to minimize wrist overuse.
Early treatment of wrist injuries: Prompt evaluation and management of wrist sprains or fractures can prevent ligament damage.
Maintain joint health: Regular exercise, a balanced diet, and managing inflammatory conditions help preserve ligament and cartilage integrity.

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