Abstract: BACKGROUND: Conventional rectangular targeting devices are divided into two modules, one left and one right, which hinders flexible intraoperative use and is prone to deformation and error. Even after connection, repeated fluoroscopic confirmation is still required for screw drilling and placement.
OBJECTIVE: To investigate the key technology development and clinical application of a modified rectangular locking device for precise distal locking screw placement in intramedullary nailing of femoral shaft fractures. 
METHODS: Medical records of patients with femoral shaft fractures admitted to Affiliated Suqian Hospital of Xuzhou Medical University and Suyu District People's Hospital from 2021 to 2023 were collected. Patients aged 18-65 years, diagnosed with femoral shaft fractures (AO classification: A, B, or C) by radiographic examination, who underwent closed reduction and intramedullary nailing with distal locking screw placement using the modified rectangular locking device, and whose clinical data (including medical history, radiographic findings, surgical records, and follow-up records) were selected. Forty-one eligible patients were included, including 30 males and 11 females, aged 20-62 years (mean, 41.17 ± 8.14 years). The following data were collected: number of intraoperative fluoroscopic examinations during distal locking screw placement, the locking success rate, the time to successful distal locking screw placement, the American Knee Society Score at 1 month after surgery and after fracture healing, and the time to fracture healing.
RESULTS AND CONCLUSION: (1) Among 41 consecutive patients with femoral shaft fractures treated via intramedullary nailing using the modified rectangular locking device, intraoperative distal locking required 0–2 fluoroscopy attempts (mean 1.1±0.5), achieved a 98% success rate, and was completed within 6–10 minutes (mean 7.0±1.5 minutes). Postoperative 1-month American Knee Society Score ranged from 140 to 190 (mean 150±15). (2) Totally 38 cases completed the 12–24 months of follow-up. Fracture healing occurred at 9–14 months (mean 10.5±2.5 months), with post-healing American Knee Society Score improving to 150–190 (mean 185±8), yielding 35 excellent and 3 good outcomes. (3) These findings indicate that freehand locking, oblique fluoroscopy-guided locking, arthroscopy-assisted locking, and electromagnetic navigation-assisted locking, the modified device eliminates dependencies on specialized equipment (e.g., arthroscopy systems or electromagnetic navigators), reduces procedural complexity, ensures high accuracy and reproducibility, significantly minimizes radiation exposure, and requires minimal surgical expertise.

Key words: femoral shaft fracture, intramedullary nail, locking screw insertion, internal fixation, modified rectangular locking device, rectangular frame-type targeting device, freehand screw insertion, oblique fluoroscopic screw insertion, arthroscopic-assisted screw insertion, electromagnetic navigation