Evaluation of ulnar styloid length

Purpose: General awareness of the ulnar styloid impaction syndrome is low and often is neglected. Radiographic evaluation of the ulnar styloid length generally includes an x-ray of the posteroanterior view. This study analyzed the effect of different radiographic views to assess the length of the ulnar styloid. The ulnar styloid-capitate ratio (SCR) expresses the relative length of the ulnar styloid, and we compare this ratio with the ulnar styloid process index (USPI). Methods: To evaluate the ulnar styloid and to analyze the effect of different radiographic views on measurement outcome, measurements were performed in 7 different radiographic positions of both wrists of 69 patients. To assess the relative size of the ulnar styloid and its impaction potential the USPI was calculated, re-evaluated, and compared with the SCR, in which the length of the ulnar styloid is divided by the length of the capitate bone. Results: The mean ulnar styloid length in all standard posteroanterior radiographs is 4.4 +/- 1.2 mm. In our population the average USPI was 0.21 +/- 0.11 and the average SCR was 0.18 +/- 0.05. The SCR has a stronger correlation with the length of the ulnar styloid than the USPI. Furthermore this new ratio eliminates differences related to gender, whereas the USPI does not. Conclusions: To identify ulnar impaction potential we recommend using the USPI, but to compare ulnar styloid between patients we recommend using the SCR obtained from neutral posteroanterior radiographs. For white patients we suggest defining a long ulnar styloid as having an SCR greater than 0.18 +/- 0.05 and/or an overall styloid length greater than 6 mm.