Ideal Length of Thread Forms for Screws Used in Screw Fixation of Nondisplaced Femoral Neck Fractures

Abstract

PURPOSE: The purpose of this study is to determine the thread length that will maximize purchase within the femoral head while minimizing risk of crossing the fracture line. Additional analysis was conducted to identify factors associated with the maximal possible length of treads in minimally and non-displaced femoral neck fractures. METHODS: We performed a retrospective study of all patients treated for a minimally or nondisplaced femoral neck fracture from April 1, 2004 through December 31, 2017. Only patients who had received a pre-operative CT or MRI scan were included. Fixation was then templated using radiographs and the distance from the subchondral bone to the fracture line was then measured. RESULTS: The study included 127 patients. The average estimated length of lag screw threads was 33.2 ± 6.67mm, with lower quartile of 29.1mm and higher quartile of 37.2mm. The median was 32.0mm and most frequently encountered estimate was 29mm. Estimated lag screw size did not differ significantly based on age or BMI, but both height (p < 0.001) and race (0.04) were positively correlated with estimated lag screw size and males had longer measurements compared to females, 37.2 ± 7.0mm vs 31.4 ± 5.7mm (p < 0.001), respectively. CONCLUSION: In conclusion, we propose an additional lag screw thread form with length 26.0mm to capture 90% of femoral neck fractures.