Eaton-Littler Staging of Thumb CMC Arthritis

Understanding why the thumb CMC joint degenerates is essential for viva questions:

• The trapeziometacarpal (TM) joint is a saddle (sellar) joint — it permits flexion-extension and abduction-adduction with a degree of rotation. This freedom of motion comes at the cost of intrinsic instability.
• The beak ligament (anterior oblique ligament — AOL) runs from the palmar ridge of the first metacarpal base to the tubercle of the trapezium. It is the primary restraint to dorsal subluxation during pinch and grip.
• With age and repetitive loading, the AOL attenuates or tears, allowing the metacarpal base to sublux dorsally. This concentrates contact forces on the dorsal articular surface, leading to cartilage loss and osteophyte formation in a predictable pattern.
• The dorsoradial ligament (DRL) and posterior oblique ligament (POL) are secondary stabilisers but are less often discussed in the Eaton-Littler context.
• Pan-trapezial arthritis (Stage IV) means the scaphotrapezial (ST) joint is also degenerate. This matters because trapeziectomy alone addresses both joints; arthrodesis of only the TM joint would leave painful ST arthritis un-treated.

Accurate staging depends on good imaging. A standard hand radiograph is often inadequate for the thumb CMC joint.

• Robert's view (hyperpronated PA): profiles the thumb CMC joint free of overlap. This is the single most useful view for staging.
• True lateral of the thumb CMC: obtained with the hand resting flat on the cassette and the thumb abducted; the X-ray beam is directed perpendicular to the trapeziometacarpal joint. Essential for assessing joint-space narrowing and dorsal subluxation.
• Stress views (forceful radial abduction of the thumb against resistance): may demonstrate dynamic instability in Stage I where static films look near-normal.
• Pitfalls: overlap of the trapezium and scaphoid on a poorly positioned lateral can falsely suggest ST joint involvement or miss it. Always confirm Stage IV on a well-positioned view before committing to pan-trapezial surgery.
• CT and MRI are not part of the standard Eaton-Littler staging (which is a plain-radiograph system) but may be used to assess the beak ligament pre-operatively or to stage the ST joint when plain films are equivocal.

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The classification is based on true lateral and AP radiographs of the thumb CMC joint (Robert's view is ideal). Four stages are defined by joint-space narrowing, osteophyte size, subchondral sclerosis, and involvement of the adjacent scaphotrapezial (ST) joint.

The grind test (axial compression and rotation of the thumb CMC) reproduces pain and crepitus in CMC arthritis, but consider:

• De Quervain's tenosynovitis — Finkelstein's test positive; pain is over the first dorsal compartment, not the CMC joint. May coexist with CMC arthritis.
• Scaphoid fracture or non-union — snuffbox tenderness; radiographic scaphoid pathology.
• ST joint arthritis without TM involvement — rare but possible; pain is more proximal. Eaton-Littler would classify this as outside the system (the TM joint is normal).
• Flexor carpi radialis tendinitis — pain volar and radial at the wrist; may mimic CMC pain but the grind test is negative.
• Carpal tunnel syndrome — paraesthesia in the median nerve distribution; night symptoms. Co-exists commonly with thumb CMC arthritis (both conditions increase with age).
• Trigger thumb — clicking or locking of the IP joint with a palpable nodule at the A1 pulley; distinct from CMC pathology.

Not every patient with thumb CMC arthritis needs surgery. Non-operative treatment is first-line for Stage I and acceptable for Stage II–III in low-demand or medically unfit patients:

• Thumb spica splinting — rest the CMC joint, particularly at night. A custom thermoplastic splint immobilising the CMC while leaving the IP free is most effective.
• Activity modification — avoid sustained lateral pinch and power grip; use ergonomic tools with larger grips.
• NSAIDs — topical or oral for symptomatic relief.
• Hand therapy — thenar strengthening (particularly opponens and abductor pollicis brevis) to compensate for CMC instability.
• Intra-articular corticosteroid injection — provides temporary relief (typically 3–6 months). Useful as a diagnostic adjunct and for patients not ready for surgery. Repeat injections carry diminishing returns and may accelerate cartilage loss.
• Hyaluronic acid injection — some evidence for short-term pain relief in Stage I–II but not superior to corticosteroid in most trials.