The Non-Union Scoring System: an interobserver reliability study

The Non-Union Scoring System (NUSS) aims to classify non-unions according to their severity and relate them to four treatment categories. The main purpose of this study was to evaluate the reliability of the NUSS. In addition we assessed its clinical validity.

Forty-four Patients with a tibia non-union between 2005 and 2015 were included in this study. Data from all included patients were scored independently by three observers according to the NUSS criteria. The interobserver agreement was evaluated using the intraclass correlation coefficient (ICC). The interobserver agreement of the Weber-Cech system was assessed using Fleiss' kappa. Finally, the clinical validity of the NUSS was analysed by comparing outcomes of the actual treatment groups to the proposed treatment groups following from the NUSS scores.

Forty-four patients were included. The comparison of NUSS scores between observers showed substantial agreement [ICC; 0.78 (0.67-0.86)]. The comparison of the Weber-Cech classification between observers showed only fair agreement [Fleiss κ; 0.30 (0.17-0.42)]. The χ² test for the treatment groups according to the NUSS and the treatments at index procedure showed an independent relation (χ² = 5.794, 6 degrees of freedom, p: 0.447). In contrast, the proposed treatment strategy corresponds well to the definitive treatment (χ² = 29.963, 9 degrees of freedom, p < 0.001).

We conclude that the NUSS is both a reliable and valid system to classify non-unions.