Distal Interlock Backout in the RFN-Advanced Retrograde Femoral Nailing System (RFNA) in Femur Fractures: Short Term Outcome Analysis.

Objective: To examine rate of distal screw backout in patients treated with the DePuy Synthes Retrograde Femoral Nail Advanced (RFNA) system.

Methods: Design: Retrospective.

Setting: Single Level I Trauma Center.

Patient selection criteria: Adults with type 32 and 33 AO/OTA femur fractures that underwent fixation between 2021 and 2024 with the RFNA. Patients were included only if they had healed fractures or demonstrated distal screw backout regardless of follow up.

Outcome measures and comparisons: Demographics, injury characteristics, fixation construct, complications such as rates of reoperation, interlock fracture, implant removal, distal screw backout ≥ 5mm and reoperation to promote bone healing were analyzed. Characteristics of patients with and without distal screw backout ≥ 5mm were compared.

Results: A total of 101 patients underwent fixation with RFNA for femur fractures. The mean patient age was of 40.4 (18-83), 62.4% were males, and mean BMI was 29.2. The average follow up was 281 days (27-1041 days). Motor vehicle accident was the most common mechanism of injury(48.5%). Fractures consisted of 77.2% AO/OTA type 32 and 22.8% type 33. Nine cases (8.9%) had screw backout (mean 15.5mm (5-31mm)). Among these 55.6% were OTA/AO 32 and 44.4% were OTA/AO 33.No cases had multiple screws backout. The mean time for diagnosis of screw backout was 73.3 days (25-180 days). Five of nine cases with backout underwent a reoperation for screw removal due to symptomatic prominence. There was a 5.0% reoperation rate to promote bone healing, a 5.0% surgical site infection rate, and a 3.0% interlock fracture rate. Excluding patients with supplemental fixation, 4 patients (5.7%) had distal screw backout with 2 undergoing removal of screw and all achieving union. No significant differences in age (37.5 vs 35.6; p=0.821), BMI (31.5 vs 29.4; p=0.607), weight bearing status (WBAT 75% vs 66.7%;p=0.134) or distance from fracture to screw (121 mm vs 132 mm; p=0.804) were observed between patients with and without backout.

Conclusion: When used for treating distal femoral and femoral shaft fractures, the Depuy Synthes RFNA showed a 8.9% rate for distal interlock screw backout ≥ 5mm and a 5% reoperation rate for removal of distal screw backout.