Hypermobility at the thumb carpometacarpal (CMC) joint has been proposed as an explanation for abnormal loading and subsequent development of osteoarthritis. Radiographic evaluation of this joint is difficult owing to the obliquity of the articulation. We modified a previously described technique to obtain a bilateral stress radiograph of the thumbs to measure CMC joint laxity. The purpose of this study was to present the details of this modified technique and evaluate its reproducibility in a group of volunteer subjects. We hypothesized that this technique would be reliable and reproducible.
A posteroanterior radiograph was obtained after asking volunteer subjects to press their thumbs together using a foam hand support. Three measurements were performed: radial subluxation of the first metacarpal base, first metacarpal articular width, and the distance between the ulnar articular facet of the trapezium and the ulnar metacarpal edge (uncovered edge). Using digital calibration on a picture archiving and communication system radiology server, a radiologist, radiology resident, orthopedic surgeon, and orthopedic resident performed measurements at 2 time points. To evaluate consistency among the raters, intraclass correlation coefficients were calculated. Test-retest bivariate analyses were performed to assess intra-rater reliability.
A total of 69 volunteers (39 women and 30 men) were imaged. Women showed significantly greater radial subluxation compared to men (p < .01). Inter-rater reliability coefficients for radial subluxation and articular width initially and at 2 weeks showed high agreement, as did test-retest reliability coefficients. For the uncovered edge measurement, inter-rater reliability coefficients were low, with wide variation in reliability.
The modified thumb CMC stress view radiograph evaluates laxity and joint abnormalities of the trapeziometacarpal articulation. The details of the radiographic technique are straightforward, and the inter- and intra-observer reliability of radial subluxation and first metacarpal width are high. The ratio of the 2 measurements provides an accurate measure of the radiographic subluxation of the first metacarpal from the trapezium. This measurement is most specific to radial subluxation under simulated active loading, in the plane of the hand. The medial uncovered edge of trapezium measurement does not have high inter-observer reliability and varies widely, and it should not be included in laxity measurements.