Association between screw angulation and union after inverted-triangle cannulated screw fixation of femoral neck fractures.

PURPOSE: The aim of this study was to evaluate whether screw angulation relative to the inter-ischial(horizontal) axis and femoral anatomical axis was associated with union after inverted-triangle cannulated screw fixation of femoral neck fractures and to explore angle intervals associated with higher union rates.

METHODS

Between January 2017 and December 2022, 83 patients operated on with closed reduction-percutaneous cannulated screws by the same surgical team were retrospectively analyzed. The angles of the calcar, anterosuperior, and posterosuperior screws were measured according to both the femoral anatomical axis and the horizontal axis. Multivariable logistic regression analyses adjusted for lateral angulation and Garden or Pauwels classification were additionally performed for the horizontal-axis screw-angle parameters. Exploratory angle intervals were assessed using quartile and sliding-window analyses.

RESULTS

A total of 64 patients achieved union, with a mean union time of 8.69 ± 3.03 weeks. The nonunion group had higher lateral angulation and greater postoperative neck length(p = 0.006, p = 0.042, respectively). In angle values relative to the horizontal axis, calcar and anterosuperior screws exhibited higher measurements in the union group(p = 0.027, p = 0.013, respectively). In exploratory sliding-window analyses, high union intervals were identified as follows: calcar 48.0-51.3°, anterosuperior 48.7–51.2°, and posterosuperior 51.8–54.0° relative to the horizontal reference; calcar 137.2–139.0°, anterosuperior 139.0-142.4°, and posterosuperior 137.6-141.7° along the anatomical axis. In adjusted analyses, the anterosuperior screw-horizontal axis angle remained associated with union across both adjusted model sets, whereas the calcar and posterosuperior screw-horizontal axis angles showed less consistent but directionally similar associations.

CONCLUSION

Greater horizontal-axis screw angulation was associated with union after inverted-triangle cannulated screw fixation of femoral neck fractures, with the most consistent adjusted association observed for the anterosuperior screw. The identified angle intervals should be considered exploratory and hypothesis-generating rather than definitive clinical targets. LEVEL OF EVIDENCE: Level III, Retrospective Observational Comparative Cohort.