Normal Bouman's Index No 2 Carpal Height on Radiography
Bouman's Index No 2 is a dimensionless radiographic ratio used to quantify carpal height — the relative longitudinal dimension of the carpus in relation to a bony reference — on posteroanterior (PA) wrist radiographs. Accurate measurement of carpal height is essential for detecting progressive carpal collapse, a hallmark of inflammatory and degenerative wrist conditions. Monitoring this index over time allows clinicians to objectively track disease progression and guide surgical planning.
Normal Reference Values
| Orientation | Location | Measurement |
|---|---|---|
| Posteroanterior | Carpal Height | 0.62-0.66 |
Clinical Significance
A normal Bouman's Index No 2 falls within the range of 0.62–0.66 on PA radiography. Values below this range indicate loss of carpal height, reflecting progressive carpal collapse commonly encountered in rheumatoid arthritis, scapholunate advanced collapse (SLAC), or scaphoid nonunion advanced collapse (SNAC). Serial measurements enable objective documentation of disease progression, particularly in patients undergoing conservative or surgical management of inflammatory arthropathy.
Pitfalls include patient positioning errors — true PA projection is mandatory, as even slight rotation alters the apparent carpal height ratio. Bony erosions in rheumatoid disease may obscure landmarks, reducing measurement reliability. Comparison with the contralateral wrist and prior studies is recommended whenever feasible.
- Rheumatoid arthritis with carpal collapse
- Scapholunate advanced collapse (SLAC wrist)
- Scaphoid nonunion advanced collapse (SNAC wrist)
- Avascular necrosis of the lunate (Kienböck disease)
- Post-traumatic carpal instability
Reference: Borisch N, Lerch K, Grifka J et al. A comparison of two indices for ulnar translation and carpal height in the rheumatoid wrist. J Hand Surg Br. 2004;29(2):144–7.
Imaging Notes
Bouman's Index No 2 is measured exclusively on a true posteroanterior (PA) radiograph of the wrist obtained with the forearm in neutral rotation and the wrist flat against the detector. Precise patient positioning is critical, as forearm rotation introduces parallax error that directly affects the ratio. The index is calculated as a ratio of specific carpal and metacarpal measurements, making reproducibility dependent on consistent landmark identification — particularly when bony erosions or degenerative changes are present.
Digital radiography with magnification tools improves landmark precision. When serial monitoring is required, standardized positioning protocols should be applied at each examination to ensure comparability across time points.