Ulnar variance - Reliability of three different methods of measurement

Ulnar variance (UV), i.e., the length of the ulna relative to the radius is a radiographic measurement commonly used to estimate fracture compression of distal radius fractures. Different methods for measuring UV have been described in the literature. The aim of this study was to assess the inter- and intra-rater reliability of three different methods of measuring UV among raters with different professional backgrounds and levels of experience.

Nine raters, one musculoskeletal radiologist, three radiology residents, one PhD student, one medical student, and three reporting radiographers, participated in the study. They measured UV on 21 radiographs using three different measurement methods: The method of central reference point (CRP), the lateral method (LM), and the method of perpendiculars (MoP). Inter-rater reliability was assessed using the intra-class correlation coefficient (ICC), while intra-rater agreement was estimated using Bland-Altman (BA) analysis with limits of agreement (LoA).

Inter-rater reliability estimated by ICCs was 0.91, 0.96, and 0.97 for the methods of CRP, LM, and MoP, respectively. Intra-rater agreement, assessed by BA LoA for rater1/rater2, was ±2.94/±1.45, ±1.92/±2.36, and ±2.14/±1.33 for the methods of CRP, LM, and MoP, respectively.

All three methods of measurement displayed excellent reliability with ICCs ranging from 0.91 to 0.97. The findings suggest that UV measurements can be reliably obtained across raters with different professional backgrounds and levels of experience using all three methods of measuring.