Determination of the safest level and screw length for the proximal locking screw in retrograde femoral nailing

Objectives: This study aims to identify the most reliable level for the proximal locking screw in retrograde femoral nails and to investigate the preoperative detectability of the length of the proximal locking screw by radiological measurements. Patients and methods: Between April 2020 and June 2021, a total of 50 patients (42 males, 8 females; mean age: 38.1 +/- 14.3 years; range, 18 to 60 years) who were suspected of vascular injury after gunshot or stab wounds and underwent lower extremity computed tomography angiography (CTA) from the local institution's database were included in the study. The distances of the femoral neurovascular structures (FNVS) and sciatic nerve (SN) to the femur were measured in the sections determined in the anteroposterior and medial-lateral planes. The anteroposterior length of the femur was measured in selected sections to estimate the appropriate length of the proximal locking screw. Results: The level at which FNVS and SN were closest to the femur in the medial-lateral plane was inferior to lesser trochanter (LT) 1 cm. The mean AP femur length at the level of the LT was 36.3 +/- 2.8 mm, at the level of inferior to LT 1 cm was 34.1 +/- 2.8 mm, at the level of superior to LT 1 cm was 38.6 +/- 3.7 mm. Conclusion: In retrograde femoral nailing, the safest level in terms of screw placement is 1 cm above the LT. Additionally, the optimal screw length is 40 mm at the level of the LT and 1 cm superior it, whereas it is 35 mm at the level of the LT and 1 cm inferior to it.