Background The etiology of trapeziometacarpal joint (TMCJ) osteoarthritis is not yet clearly confirmed. Laxity of the TMCJ is considered as one of the causes of osteoarthritis. Previous studies evaluated the relationship between the bony morphology and TMCJ laxity mainly in osteoarthritic TMCJs. It is unclear, however, whether there is such relationship in non-arthritic TMCJ.

Objectives We aimed to determine whether the articular surface projection was associated with laxity of the TMCJ.

Methods We measured the trapezial tilt and the first metacarpal base articular slope in radiographs of 108 women without thumb TMCJ osteoarthritis. The mean age was 57 years (range, 32 to 79 years). The trapezial tilt (TT) was defined as the angle formed by the intersection of a tangent to the middle third of the distal trapezial articular surface and a line parallel to the longitudinal axis of the index metacarpal in the posteroanterior radiograph of the trapezium (α in Fig 1A). The metacarpal articular slope (MS) was defined as the angle between the dorsal cortex and the articular surface of the first metacarpal base in a true lateral view of the thumb metacarpal (β in Fig 1B). We evaluated the radiologic laxity of the TMCJ using subluxation ratio (SR) in the TMCJ stress view radiograph (RS (radial subluxation)/AW (articular width) in Fig 1C). We divided the subjects into four subsets according to the TT and MS, and compared the mean SR between the upper and lower quartile groups.

Results There was a statistically significant difference in the mean SR between those in the upper and lower quartiles of the MS (0.24 vs 0.32, P=0.013). However, there was no difference in the SR with regard to the TT (P=0.189).

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Conclusions This study suggests that a steeper articular slope of the first metacarpal base could be associated with radiologic laxity of the TMCJ. Further longitudinal studies are necessary to determine whether this anatomic difference represent a risk factor for later development of TMCJ osteoarthritis.

Disclosure of Interest None declared