Risk factors for nonunion in initial surgery for scaphoid nonunion

Although there have been many studies on postoperative risk factors for scaphoid nonunion, the failure rate is still reported to be 10-30%.

In this study, we retrospectively examined the factors that led to postoperative nonunion in 87 patients (82 male and 5 female) who underwent initial surgery using free bone graft for scaphoid nonunion between 2008 and 2022. Nonunion was defined as no evidence of union on plain radiography or Computed tomography (CT) 3 months after injury. Cases in which bone union could be confirmed only by the initial surgery were defined as the union group, and those in which bone union could not be confirmed by plain radiography or CT at the final examination or those who underwent reoperation were defined as the nonunion group. Age, BMI, smoking history, time since injury, lunate type, ratio of proximal scaphoid fragment volume to total scaphoid volume (Proximal Ratio: PR), presence of sclerotic or cystic changes, MRI signal changes in the proximal scaphoid fragment, source of bone graft, fixation materials, pre- and postoperative radio-lunate angle, its correction, direction of screw insertion, direction of fracture line were examined. Volume was measured using Mimics 21.0 (Materialise, Leuven, Belgium) and a 3D model was created from preoperative CT in all cases

Nonunion was observed in 15 patients after the initial surgery, and the nonunion rate was 17.2%. Univariate analysis showed that the source of bone graft and PR had p values less than 0.05, but multivariate analysis showed that only PR was an independent factor (p = 0.03).

Small PR was the only factor that led to nonunion after the initial surgery. Both biological and biomechanical aspects seem to be involved, and it is necessary to approach surgery with attention to both sides.

Keywords: scaphoid nonunion, bone volume