Radiographic assessment of the trapezial space before and after ligament reconstruction and tendon interposition arthroplasty.

A radiographic method was developed, the trapezial space ratio, for assessing the space occupied by the trapezium (a space defined by the distal scaphoid and thumb metacarpal base divided by the thumb proximal phalanx). This method was applied to 100 normal thumb radiographs and to the radiographs of 15 patients with symptomatic degenerative arthrosis of the thumb basal joint before and after operative treatment with ligamentous reconstruction and tendon interposition arthroplasty. The trapezial space ratio averaged 0.476 +/- 0.033 for radiographs of normal thumbs, 0.372 +/- 0.084 for the pre-operative radiographs of thumbs with symptomatic basal joint arthrosis, and 0.270 +/- 0.078 for the radiographs of thumbs following basal joint arthroplasty. A significant reduction in the trapezial space ratio was noted when values from arthritic thumbs were compared to those of normal thumbs (22%; P < 0.0001). A further reduction in the trapezial space ratio was noted when post-operative values were compared to pre-operative ones (27%; P < 0.0002). Comparing post-operative trapezial space ratio values to values obtained in normal thumbs, a reduction of 43% was found in those thumbs treated operatively. These finding indicate that the trapezial space is reduced significantly in thumbs with severe degenerative arthrosis compared to normal thumbs and that ligament construction tendon interposition arthroplasty is not entirely successful in either restoring or maintaining the length of the thumb ray.