Risk Factors That Cause Delayed Union after Surgery for Acute Scaphoid Fracture

<b>Background:</b> It is important to prevent delayed union after surgical treatment for acute scaphoid fractures; however, risk factors remain to be elucidated. We investigated the risk factors for delayed union in cases of scaphoid fractures with surgical treatment at our hospital. <b>Methods:</b> We enrolled 29 patients with scaphoid fracture who underwent percutaneous screw fixation at Juntendo University Hospital between January 2015 and February 2024. Patients were divided into a U group consisting of those who achieved bone union at 6 months after surgery, and a D group consisting of those who had delayed union. The evaluation items were: age, smoking, occupation, fracture type (Herbert classification, Schernberg classification), duration from injury to surgery, displacement measurement preoperative intrascaphoid angle (ISA), postoperative ISA, preoperative scapholunate angle (SLA) and postoperative SLA. <b>Results:</b> Delayed union was observed in eight cases. Bivariate analysis showed that duration from injury to surgery, displacement measurement, preoperative ISA and preoperative SLA were significantly associated with delayed union (<i>p</i> = 0.002, <i>p</i> = 0.006, <i>p</i> < 0.001 and <i>p</i> = 0.008, respectively). Furthermore, we found a significant positive correlation between preoperative ISA and the duration from injury to surgery, and between preoperative ISA and preoperative SLA. <b>Conclusions:</b> Delayed union was associated with duration from injury to surgery, humpback deformity and instability between the scaphoid and lunate. While the factors were statistically correlated, both are important clinical considerations for surgeons. <b>Level of Evidence:</b> Level III (Therapeutic).