Varus mal-alignment and residual displacement are associated with delayed union in subtrochanteric femur fracture- A retrospective observational study

Background: Subtrochanteric femoral (ST) fractures are associated with high rates of delayed and non-union. The aim of this study was to analyse the risk factors associated with delayed/non-union in ST fractures.Methods: All patients with surgical stabilisation of ST fractures during the period 2014 to 2019 were identified in an electronic patient records database in two trauma centres. Exclusion criteria were incomplete clinical/ radiological data, pathological fractures and loss to follow-up. Radiographs at about 6 months post-surgery were assessed for fracture union using Radiographic Union Score for Hip (RUSH). Fracture was deemed to be un-united if RUSH score was <18. CCD (caput-collumdiaphyseal) angle of operated and uninjured hip, residual displacement at fracture site and 3-point relationship was calculated on operative or immediate post-operative images in both groups. Student's t-test was used to compare CCD angle difference between operated and un-injured sides and the residual fracture displacement between delayed union and united fractures group. Chi-square test was used for 3-point relationship. Observational analysis was performed on implant failure rates including distal screw breakage.Results: During the study period, there were total of 278 patients. 193 with inadequate data and 22 with pathological fractures were excluded. Advanced age and female sex had significantly higher rate of delayed union (p value of 0.043 and 0.003 respectively). Delayed union group (26) had a mean RUSH score of 14.1 and united group (37) had a mean RUSH score of 26.3 (p = 0.019). The mean CCD angle difference between operated and uninjured sides was - 5.77(degrees) for delayed union and - 2.33(degrees) for united fractures (p = 0.03). Residual displacement at fracture site showed statistically significant difference between delayed union and united fractures on ante-roposterior and lateral views (p = 0.001 each). There was no statistical difference in 3-point relationship of implant in two groups (p = 0.775). 10 revision procedures were performed for implant failures. Distal screw failure (3 cases) was not a precursor for non-union in this study.Conclusion: This study confirms varus alignment of hip and residual fracture displacement after fracture fixation of subtrochanteric fracture are surgeon associated significant risk factors for delayed union at 6 months. Fracture contact and alignment are key to reduce failures in these group of fractures. Among patient factors, advancing age and female sex predisposes to higher rate of delayed union.