The Importance of Flare: A Radiological Evaluation of Fixed-Angle Guide and Barrel-Plate in Sliding Hip Screws.

Background and objective The sliding hip screw (SHS) remains the main operative implant of choice for A1/2 intertrochanteric fractures. These implants are often fixed-angled with a corresponding guide to decrease inventory and implant cost. However, there are varying sizes of base plates on the fixed-angle device between industries. Screw placement is crucial to achieving optimal tip-apex distance (TAD) and position. Due to the flare of the greater trochanter (GT), we hypothesise that the fixed-angle guide can lead to malpositioning. In this study, we aimed to describe the discrepancy between the fixed-angle guide (short: 38 mm, long: 60 mm), the flare of the GT, and the effects on screw placement. Methods Patients who received SHS between August to December 2019 were evaluated. We measured the neck-shaft angle, GT flare angle to the femoral axis, screw-plate angle, screw position, and TAD. We templated the optimal 135° fixed-angle barrel-plate, angle guides, and measured the divergence between the angles. Results A total of 30 patients were identified to be included in the study; 24/30 (80%) were female, with 16/30 (53%) receiving SHS on the right hip. The average age of the participants was 82 ±9 years. The average neck-shaft angle was 132.4° ±5.9. The GT flare angle was 3.2° ±1.6. Of note, 66% of patients had a screw-plate angle of ≥135° with an average of 137° ±3.7. However, only 10/30 (33%) screws were placed superiorly, with an average TAD of 21 mm ±11 compared to screws placed in the centre and inferiorly at 9.5 mm ±3 (p=0.0004). The long fixed-angle guide resulted in a lower divergence angle at 3° ±1.7 compared to 5.2° ±2.6 for the short fixed-angle guide (p=0.0001). Conclusion Using the fixed-angle guide at 135° on the GT flare results in a sub-optimum screw-plate angle. This can lead to malpositioning of the screw, as well as increased TAD and screw-plate angle. Preoperative planning is crucial to measure the femoral neck-shaft angle, GT flare, as well as utilising a longer fixed-angle guide.