Sensitivity and specificity of 3D models of the radioulnar joint cup in combination with a sphere fitted to the ulnar trochlear notch for estimation of radioulnar incongruence in vitro.

Objective: To determine the sensitivity and specificity of estimation of radioulnar incongruence (RUI) by use of 3-dimensional (3D) image renderings in combination with a sphere fitted to the ulnar trochlear notch.

Study Design: In vitro study.

Sample Population: Right forelimbs (n = 8) of canine cadavers weighing >20 kg.

Methods: CT-based 3D models (n = 63) of the radioulnar joint cup with different states of RUI were used. A sphere was fitted to the trochlear notch of each of the models and 2 independent observers estimated RUI based on the relation of the sphere and the radial joint surface blinded to the true state of RUI at 1 mm precisely (-2 mm to +2 mm).

Results: Mean sensitivity and specificity for detecting any form of incongruent joint was 0.94 and 0.89, respectively. Evaluating a positive step (short radius) versus a congruent joint resulted in a mean sensitivity and specificity of 0.89 and 0.96, respectively. A negative RUI (short ulna) was diagnosed with a mean sensitivity and specificity of 1.00 and 0.92, respectively. Intra-class-correlation coefficient for inter-observer agreement was 0.99.

Conclusions: Fitting a sphere to the ulnar trochlea notch significantly improves diagnostic accuracy of 3D models of the radioulnar joint cup when diagnosing RUI.