Flexible Use of the NUSS in Non-Union Surgery: Value of Intraoperative Bone Loss Assessment and Overtreatment

Abstract Background The Non-Union Scoring System (NUSS) is the first multidimensional tool to guide treatment of fracture non-unions, but key parameters—particularly bone loss—may be underestimated preoperatively. We assessed (i) how intraoperative reassessment modifies NUSS scoring and algorithmic recommendations and (ii) whether our centre’s frequent use of combined mechanical and biological strategies (“overtreatment”) affects outcomes versus the Calori validation cohort. Methods We retrospectively reviewed 103 adults surgically treated for long-bone non-union at Cliniques Universitaires Saint-Luc (Brussels) from 2015–2023 with ≥12-month follow-up. NUSS was calculated preoperatively and recalculated immediately post-debridement from radiographs/CT; patients were stratified into NUSS therapeutic groups and compared with Calori et al. (2014). Outcomes were union, time to radiographic consolidation, and complications, analysed with binomial and Student’s t-tests (α=0.05). Results The tibia was the most affected site (54.4%), with high prevalence of infection (42.7%) and repeated surgery (≥2 procedures in 70%). Intraoperative reassessment revealed significantly larger bone defects, especially in group 3 (7.2 → 10.5 cm, p < 0.001), leading to NUSS score changes in 18 patients (17.5%), with reclassification in 2 cases (1.9%). In comparison with NUSS recommendations, overtreatment occurred frequently (94% in group 1, 87% in group 2), attributable to the recurrent, albeit non-systematic, use of biological stimulation. The overall union rate in our series was 83.0%, comparable to 85.5% in Calori’s cohort. Group 1 patients achieved higher union rates (97.0% vs. 86.9%, p = 0.058) and significantly shorter healing times (7.8 ± 1.6 vs. 8.8 ± 2.0 months, p = 0.04). No significant differences were found in groups 2 and 3, where outcomes were negatively influenced by infection and smoking. Conclusions The NUSS provides a robust framework for classification and treatment planning in non-unions, but intraoperative reassessment is essential to avoid underestimation of bone loss. Proactive addition of biological augmentation to mechanical revision achieved very high union and shorter healing in simple non-unions without added morbidity; benefits were less evident in complex cases, where infection and adverse biology predominate. NUSS should therefore be applied as a flexible guide, complemented by clinical judgment and tailored biological strategies.