Evaluation of ulnar variance on wrist MR imaging: is it a reliable measure?

To determine if ulnar variance can be evaluated by magnetic resonance (MR) imaging and if this measure can be used as a reliable indicator when correlated to the gold standard technique, conventional radiography (CR).

From January to July 2018, the MR images of 64 participants, comprising 66 wrists (mean age 34.9 years; 33 females; 31 males), were obtained. Among those, 29 were referred for evaluation of the wrist for different medical reasons and 35 were asymptomatic volunteers from our radiology group. All subjects had a plain radiography of the wrist in a posteroanterior view with a mean interval between images of 1 day. Local ethics committee approved the study and written informed consent was obtained from all patients. Two musculoskeletal radiologists evaluated the images. Correlation coefficients and a linear regression model were used for statistical analyses.

Intra- and inter-observer analyses were performed for both diagnostic methods with results showing concordance (intra-observer: kappa score: MR 0.915/CR 0.931; p < 0.05; inter-observer: kappa score: MR 0.857/CR 0.931; p < 0.05). The intraclass correlations of MR and CR to evaluate agreement between the radiologists was slightly higher for radiologist #1 (0.771) than for radiologist #2 (0.659). A linear regression model showed good model fit indicating that MR does correlate with the ulnar variance as measured by CR (CR = 0.554 + 0.897 × MR, R² = 0.665).

Although CR is the gold standard method for the evaluation of ulnar variance, our study demonstrated that MR can be used as a reliable qualitative option.