Lunate morphology as a risk factor of idiopathic ulnar impaction syndrome

Positive ulnar variance is an established risk factor for idiopathic ulnar impaction syndrome (UIS). However, not all patients with positive ulnar variance develop symptomatic UIS and other factors, including the morphology of the lunate, may be involved. The aim of this study was to clarify the relationship between lunate morphology and idiopathic UIS.

A cohort of 95 patients with idiopathic UIS (UIS group) was compared with 95 asymptomatic controls with positive ulnar variance. The shape of the lunate was measured using the capitate-triquetrum distance (CTD), ulnar coverage ratio (UCR), radiolunate distance and radiolunate angle. The association of radiographic parameters and lunate types with the development of UIS was investigated in univariable and multivariable analyses. Receiver operating characteristic curves were used to estimate a cutoff for any statistically significant variables.

The proportion of type II lunates, which have a medial hamate facet, were significantly higher in the UIS group than in the control group in the univariable analysis (p = 0.001). CTD (odds ratio (OR) 1.52; 95% confidence interval (CI) 1.11 to 2.06; p = 0.008) and UCR (OR 44.78; 95% CI 5.35 to 374.90; p = 0.002) showed a positive association with UIS in the multivariable analysis. Estimated cutoff values were 2.5 mm for the CTD (area under the curve (AUC) = 0.65) and 0.4 for the UCR (AUC = 0.64).

The proportion of type II lunates was greater in the UIS group than in the control group. A large UCR, which represents the broad base of the lunate, was positively associated with the development of idiopathic UIS. Cite this article: Bone Joint J 2017;99-B:1508-14.