Clinical Characteristics of Patients with Long-Bone Fracture Nonunion and Delayed Union and Factors Associated with Infection: A Retrospective Single-Center Cohort Study

Background/Objectives: To evaluate the clinical and demographic characteristics of patients with impaired union of long bone fractures admitted to a specialized orthopedic center and to identify factors associated with infection on admission. Methods: A retrospective, single-center cohort study was conducted at the National Scientific Center of Traumatology and Orthopedics named after Academician N.D. Batpenov. The study included patients hospitalized between 2023 and 2025 with diagnoses of fracture nonunion or delayed union. Demographic characteristics, lesion location, interval from injury to hospitalization, previous treatment, presence of revision osteosynthesis, infection on admission, and length of hospitalization were analyzed. Univariate analysis and multivariate logistic regression were used to identify factors associated with infection. Patients with osteomyelitis were excluded from the regression model to avoid definitional collinearity. Results: During the study period, 360 hospitalizations were recorded in 336 unique patients. The annual incidence increased from 79 in 2023 to 166 in 2025. The median patient age was 50 years, with women accounting for 52.5% of the sample. The most common bone sites were the femur (36.1%), humerus (23.6%), and tibia (15.0%). The median interval from injury to hospitalization at a specialized center was 2 years. Prior revision osteosynthesis was noted in 34.2% of patients. Infection on admission was detected in 20.3% of patients and was associated with a longer hospital stay. In an exploratory multivariable model (EPV ≈ 2.8), previous revision osteosynthesis was associated with infection on admission (OR 8.26; 95% CI 2.76–24.74; p < 0.001). Conclusions: Patients with nonunion and delayed union of long-bone fractures referred to a specialized center represent a clinically complex population characterized by prolonged time from injury, previous surgical interventions, and a substantial burden of infection. In an exploratory multivariable analysis, previous revision osteosynthesis was associated with infection on admission and may represent a marker of clinical complexity and prior treatment burden rather than a causal determinant of infection. Further prospective studies are required to clarify factors associated with infection and treatment outcomes in this patient population.