Thumb CMC Joint Osteoarthritis: Testing, Diagnosis, and What to Expect

How Do You Test for CMC?

Testing for Carpometacarpal (CMC) joint osteoarthritis, particularly of the thumb, involves a comprehensive approach combining a detailed patient history, specific physical examination maneuvers such as the Grind Test, and confirmatory imaging studies like X-rays.

Understanding CMC Joint Osteoarthritis

The Carpometacarpal (CMC) joint of the thumb, also known as the basal joint, is formed by the articulation of the trapezium carpal bone and the first metacarpal bone. This saddle-shaped joint allows for a wide range of motion, including flexion, extension, abduction, adduction, and opposition, which are crucial for the thumb's ability to pinch, grasp, and manipulate objects.

Due to its high mobility and the significant forces it endures during daily activities like gripping, pinching, and twisting, the CMC joint is highly susceptible to degenerative changes, leading to osteoarthritis (OA). CMC joint OA is a common condition, particularly affecting women over 40. It results in the breakdown of articular cartilage, leading to pain, stiffness, and functional impairment.

Initial Assessment: Patient History and Symptoms

The diagnostic process begins with a thorough patient history to understand the nature and progression of symptoms. Key information includes:

• Common Symptoms: Patients typically report pain at the base of the thumb, often radiating into the wrist or forearm. This pain is usually aggravated by activities involving pinch, grip, or twisting movements. Other symptoms include stiffness, especially in the morning or after periods of inactivity, weakness in pinch or grip, and a sensation of grinding or clicking within the joint.
• Aggravating Factors: Activities that commonly exacerbate pain include opening jars, turning keys, writing, knitting, using tools, or performing any task requiring a strong thumb pinch.
• Relieving Factors: Rest or the application of ice may provide temporary relief.
• Impact on Daily Life: Understanding how the symptoms affect daily activities, work, and hobbies provides insight into the severity of the condition.

Physical Examination Tests for CMC Joint Osteoarthritis

A hands-on physical examination is crucial for confirming the diagnosis and ruling out other conditions.

• Inspection and Palpation:
  • Inspection: The examiner will look for visible swelling, redness, or deformity at the base of the thumb. In advanced cases, a "shoulder sign" (a squared-off appearance due to subluxation of the metacarpal) may be present.
  • Palpation: Tenderness will typically be elicited directly over the CMC joint, specifically over the trapezium and the base of the first metacarpal.
• Grind Test (Axial Compression and Rotation Test): This is the most specific and widely used clinical test for CMC joint OA.
  • Procedure: The examiner grasps the patient's thumb metacarpal and applies axial compression (pushing the thumb towards the wrist) while simultaneously rotating the metacarpal at the CMC joint.
  • Positive Sign: A positive test is indicated by the reproduction of the patient's pain and/or the sensation of crepitus (grinding or grating) within the joint, signifying cartilage degeneration.
• Adduction Stress Test: While less specific than the Grind Test, this can assess stability.
  • Procedure: The examiner stabilizes the wrist and applies an adduction force to the thumb metacarpal.
  • Positive Sign: Pain or instability may indicate CMC joint laxity or degeneration.
• Range of Motion (ROM) Assessment:
  • Active and Passive ROM: The examiner assesses the active and passive range of motion of the thumb CMC joint in all planes (flexion, extension, abduction, adduction, and opposition). Limited or painful motion, particularly during opposition and abduction, is common.
  • Crepitus: The examiner may also feel for crepitus during active or passive movement, which indicates roughened articular surfaces.
• Strength Testing:
  • Pinch Strength: Reduced pinch strength (e.g., tip-to-tip, key pinch, palmar pinch) is a common finding due to pain and muscle weakness. A dynamometer can be used for objective measurement.
  • Grip Strength: While less directly affected than pinch strength, overall grip strength may also be diminished.

Imaging Studies for Confirmation

Imaging plays a vital role in confirming the diagnosis and assessing the severity of CMC joint OA.

• X-rays:
  • What they show: Standard radiographs are typically the first-line imaging modality. They can reveal characteristic signs of OA, including joint space narrowing (loss of cartilage), osteophytes (bone spurs), subchondral sclerosis (increased bone density beneath the cartilage), and subchondral cysts.
  • Views: Specific views, such as the Robert's view (an oblique view of the thumb CMC joint) or stress views, may be obtained to better visualize the joint space and assess for subluxation.
• MRI/CT Scans:
  • When they might be used: While not routinely necessary for diagnosing typical CMC OA, MRI (Magnetic Resonance Imaging) or CT (Computed Tomography) scans may be utilized in cases where the diagnosis is unclear, to rule out other pathologies (e.g., soft tissue injuries, other carpal bone issues), or to assess the extent of bone and soft tissue involvement more precisely, especially if surgical intervention is being considered.

Differential Diagnosis

It is important to differentiate CMC joint OA from other conditions that can cause similar symptoms at the base of the thumb or wrist. These include:

• De Quervain's Tenosynovitis: Inflammation of the tendons on the thumb side of the wrist. Finkelstein's test would be positive.
• Scaphoid Fracture: A fracture of the scaphoid bone in the wrist. Tenderness in the anatomical snuffbox is a key indicator.
• Wrist Ganglion Cyst: A fluid-filled lump that can cause localized pain.
• Carpal Tunnel Syndrome: Nerve compression in the wrist, causing numbness, tingling, and weakness in the hand and fingers (typically thumb, index, middle, and half of ring finger).
• Other Arthritis Forms: Such as rheumatoid arthritis or psoriatic arthritis, which typically affect multiple joints and have systemic symptoms.

Conclusion: A Comprehensive Diagnostic Approach

Diagnosing CMC joint osteoarthritis relies on a holistic approach. A thorough medical history detailing the onset and nature of pain, combined with a meticulous physical examination that includes specific provocative tests like the Grind Test, forms the cornerstone of diagnosis. Imaging studies, primarily X-rays, serve to confirm the clinical findings and provide an objective assessment of the joint's degenerative changes. This comprehensive evaluation ensures an accurate diagnosis, leading to appropriate management and treatment strategies to alleviate pain and improve function for individuals affected by CMC joint OA.