Normal Carpometacarpal Joint Space Size on Radiography
The carpometacarpal (CMC) joints are articulations between the distal carpal row and the bases of the five metacarpals, providing both stability and mobility to the hand. Accurate assessment of CMC joint space width on radiographs is essential for detecting early articular disease, post-traumatic changes, and instability. Recognizing the normal 1–2 mm joint space allows clinicians to identify subtle narrowing or widening that may alter patient management.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Posteroanterior, Lateral | 1-2 mm |
Clinical Significance
A CMC joint space measuring less than 1 mm suggests joint space narrowing, most commonly due to osteoarthritis — particularly at the first CMC (trapeziometacarpal) joint, which is one of the most frequently affected sites in the hand. Narrowing may also result from inflammatory arthropathies, post-traumatic arthrosis, or avascular necrosis of adjacent carpal bones. Conversely, widening beyond 2 mm can indicate ligamentous disruption, dislocation, or an effusion.
Asymmetric joint space loss compared with the contralateral hand is a useful diagnostic clue. Subchondral sclerosis, osteophyte formation, and periarticular erosions should be assessed concurrently, as isolated joint space measurement provides limited diagnostic information without these contextual findings.
- First CMC osteoarthritis (Bennett fracture sequela or primary)
- Rheumatoid arthritis with erosive CMC involvement
- Psoriatic or reactive arthropathy
- Post-traumatic CMC dislocation or instability
- Calcium pyrophosphate deposition (CPPD) disease
Reference: Müller TB. Normal Findings in Radiology. Thieme. (2000).
Imaging Notes
CMC joint spaces are evaluated on standard posteroanterior (PA) and lateral radiographic projections of the hand and wrist. The PA view, obtained with the hand flat on the detector and the beam centered over the mid-carpus, provides the clearest depiction of the second through fifth CMC articulations. The first CMC joint is best assessed on a dedicated Robert view (true AP with the thumb abducted and internally rotated) or a stress PA projection. On the lateral view, the CMC joints are frequently superimposed, limiting their individual assessment but allowing identification of dorsal or volar dislocation.
Measurement should be performed at the narrowest visible portion of the joint space using a consistent window/level setting on digital systems. Oblique views can supplement standard projections when clinical suspicion for isolated CMC pathology is high. Comparison with the contralateral hand is recommended when asymmetric disease is suspected.