Length-stable fixation reduces femoral neck shortening in unstable femoral neck fractures: A retrospective comparative study of length-stable dynamic hip screw versus femoral neck system fixation

Background Femoral neck shortening following internal fixation of unstable femoral neck fractures can compromise functional recovery, particularly in young, active patients. This study aimed to evaluate the efficacy of a length-stable dynamic hip screw (LSD) construct in minimizing postoperative shortening compared to the femoral neck system (FNS). Methods A retrospective review was conducted on 65 patients with high-grade unstable femoral neck fractures treated between February 2016 and February 2023 at a single institution. Patients underwent either FNS ( n = 31) or LSD ( n = 34) fixation. Femoral neck shortening was quantified using vector-based analysis derived from contralateral femoral comparison at final follow-up. Functional outcomes were assessed using the Hip Disability and Osteoarthritis Outcome Score (HOOS). Results The LSD group demonstrated significantly less femoral neck shortening compared to the FNS group (5.0 ± 4.6 mm vs 10.4 ± 6.7 mm, p = 0.001). Final HOOS scores were significantly higher in the LSD group in the symptom (88.1 vs 75.8, p = 0.049) and stiffness subdomains. Union was achieved in 31 of 34 patients (91.2%) in the LSD group and 26 of 31 (83.9%) in the FNS group ( p = 0.605). Other complications were more frequent in the FNS group but did not reach statistical significance. Conclusion Length-stable fixation using the LSD construct significantly reduced postoperative femoral neck shortening in high-grade unstable fractures, without compromising union rates or functional recovery. Our results support the role of length-stable constructs as a reliable option for maintaining anatomic integrity in unstable femoral neck fractures.