Correlations Among Ulnar Variance, Ulnar Styloid Length, and Lunate Type: Implications for Wrist Impaction Syndromes.

Background: Ulnar wrist complaints are common but difficult to diagnose due to the complex anatomy of the wrist. Ulnar impaction syndrome (UIS) is associated with positive ulnar variance but can also occur with neutral or negative variance. Other causes include an elongated ulnar styloid and a type II lunate. This study sought to determine the prevalence of these conditions and their relation with UIS in a large population. Methods: Approximately 7000 wrist radiographs were evaluated for neutrality, of which 1780 were included. Trained observers measured ulnar variance and ulnar styloid length, and calculated the ulnar styloid process index (USPI) and styloid-capitate ratio (SCR). The lunate type was also classified. Results: Average ulnar variance was found to be 0.19 mm, with a mean ulnar styloid length of 5.45 mm. The USPI averaged 0.27, and the SCR was 0.23. Depending on the thresholds (1 and 2 mm), 11%-30% exhibited positive ulnar variance. Seven percent of patients underwent ulnar shortening osteotomy. An elongated ulnar styloid was observed in 32% of wrists, with only 1 case of UIS due to an elongated ulnar styloid. Type II lunate was more prevalent than type I (56% versus 44%), with possible left-right discrepancies. Conclusions: Ulnar plus variance is common but infrequently causes symptoms, even in cases with neutral or negative ulnar variance, highlighting its dynamic nature. The USPI is the best measure for impaction risk, whereas SCR refines styloid assessment. Lunate type did not influence the decision for surgery, emphasizing the need for dynamic, multifactorial wrist evaluation for accurate diagnosis and management.