Hand Orthopedics Rhizarthrosis Criteria Calculator

About rhizarthrosis (thumb CMC osteoarthritis)

Rhizarthrosis is osteoarthritis of the trapeziometacarpal (TMC) joint, which is the first carpometacarpal (CMC) joint sitting at the base of the thumb. Its saddle shape is what gives the thumb the broad range of motion you rely on for pinching and gripping, and that same mobility is part of why it wears down so often. It ranks among the most common spots for arthritis in the hand, and older women are affected far more than anyone else. People describe pain at the base of the thumb, a weak pinch and grip, and trouble with everyday things like turning a key or twisting open a jar.

Clinical criteria and how it is assessed

The diagnosis is made clinically, with radiographs backing it up. Here are the findings that feed into this calculator:

• Tenderness when you press directly over the thumb CMC joint.
• A positive grind test, where axial compression combined with rotation of the metacarpal brings back the pain and crepitus. Specificity runs high, around 100%, though sensitivity is lower.
• Other provocative maneuvers, like the metacarpal pressure-shear test, which has been reported with high diagnostic accuracy and sensitivity.
• A weak or painful pinch. In advanced disease you may see a "shoulder sign" prominence at the joint base, or a compensatory hyperextension (zigzag) of the metacarpophalangeal joint.
• Radiographic staging using the Eaton-Littler classification. Stage I is slight joint widening; stage II shows narrowing with osteophytes under 2 mm; stage III is narrowing with osteophytes over 2 mm; stage IV adds scaphotrapezial involvement.

Who uses this

Orthopedic and hand surgeons reach for these criteria, and so do rheumatologists, residents, hand therapists and physiotherapists. They use them to stage the disease and to decide whether a splint, an injection or surgery makes the most sense.

FAQ

What is the grind test? The examiner presses and twists the thumb metacarpal against the trapezium. If that brings on pain and a grinding feeling, CMC arthritis is likely.

What does Eaton-Littler staging do? It puts a grade on what the X-rays show, running from early joint changes at stage I up to scaphotrapezial involvement at stage IV, and that grade helps guide treatment.

This tool is educational only and does not replace a medical evaluation. If pain at the base of the thumb sticks around, have a qualified clinician examine it, order imaging and manage it.