Retrospective evaluation of factors affecting fracture healing following intramedullary nail application in humeral shaft fractures

Humeral shaft fractures are defined as fractures occurring from the attachment site of the pectoralis major muscle proximally to the supracondylar region distally. It is reported that they comprise approximately 3% of all orthopedic injuries. The primary goal in the treatment of humeral shaft fractures is to achieve proper alignment, maintain suitable length and rotation, and provide optimal conditions for healing. Simultaneously, early joint mobility should be facilitated. When performed with appropriate technique, intramedullary nailing (IMN) offers advantages such as supporting fracture union, shorter surgical duration, minimal scarring, and lower risks of infection and postoperative osteomyelitis. Moreover, this technique allows patients to mobilize and weight-bear earlier, thus easing the treatment process. This single-center retrospective study aims to evaluate factors affecting fracture healing after treatment of humeral shaft fractures with intramedullary nails. The core focus of the research was to identify the optimal intramedullary nail diameter/istmus ratio that positively influences union and to investigate the effect of distraction on healing in patients who underwent humeral IMN. Between November 2014 and January 2024, 79 patients who had undergone intervention for humeral shaft fractures with locked intramedullary nails at the Orthopedics and Traumatology Department of Akdeniz University Hospital were included. Patients lost to follow-up, those who could not be reached with postoperative radiographs, patients who died before completing one year of followup (n=3), patients diagnosed with pathological humeral shaft fractures via intramedullary nailing (n=5), and those treated with other surgical methods but developed pseudoarthrosis (n=5) were excluded from the study. Ultimately, 64 patients with humeral shaft fractures were included. The ratio of nail diameter to isthmus diameter was determined for all cases. Patients' radiographs at 6 weeks and at 3, 6, 9, and 12 months postoperatively were 83 examined, and healing was assessed using the RUSHU scoring system with average scores obtained. To determine the effects of other potential factors—such as demographic features, clinical findings, and radiological measurements—on fracture healing, univariate and multivariate statistical analyses were performed. Regarding the relationship between the nail diameter/istmus ratio and healing, ROC analysis revealed that the ratio had a cut-off value of 0.8242 at 6 weeks for predicting union, with 89.3% sensitivity and 50% specificity (AUC=0.761, p=0.018). For predicting union at 3 months, the cut-off was 0.8152 with 91.4% sensitivity and 66.7% specificity (AUC=0.825, p=0.009). Another radiological parameter, postoperative distraction distance, was found to significantly affect healing. Logistic regression analysis showed that increased distraction distance was a significant risk factor for non-union. An increase of 1 mm in distraction raised the risk of non-healing approximately 6.26 times (95% CI: 1.060-36.953, p=0.043). Other parameters, including alcohol and cigarette use, were statistically associated with impaired healing. No significant relationship was found between union and the following factors: patient's injury side, mechanism of injury, presence of multitrauma, head trauma, whether the fracture was open or closed, diabetes mellitus, fracture location (diyaphyseal), AO/OTA classification, distraction distance, nail diameter/istmus ratio, olecranon fossa apex-to-nail tip distance, number of distal locking screws, or the ratio of the distances from distal locking screws to the fracture line relative to nail length. Additionally, no significant relationship was observed between union and variables like injury side, injury mechanism, multitrauma, head injury, open vs. closed fracture, diabetes, fracture site, distraction distance, nail diameter/istmus ratio, olecranon fossa apex-to-nail tip distance, number of distal screws, or ratios of screw distances to nail length.