Two headless cannulated screws have a higher maximum failure load than screw-and-pin fixation at a 70° fracture angle in 3-dimensionally printed canine femoral neck models

Objective: To compare maximum failure load among 3-D-printed canine femoral neck models differing in fracture angle and fixation configuration. Methods: This experimental biomechanical study was conducted in a university research laboratory from September 10, 2025, through March 10, 2026. Polycarbonate 3-D-printed models were created using left femoral CT data from a 2-year-old 11.9-kg Shiba Inu. The group configurations were a 50° femoral neck fracture stabilized with one 2.5-mm fully threaded headless cannulated screw (HCS) and an antirotation pin (1S1P50), a 70° fracture with the same fixation (1S1P70), and a 70° fracture stabilized with 2 parallel 2.5-mm HCSs (2S70). Initial construct stiffness was estimated from load-crosshead displacement curves. Maximum failure load, the primary outcome, was determined under single axial compression of the femoral head. Results: 18 models were analyzed, with 6 in each group. There was no difference in initial construct stiffness among groups. Mean maximum failure loads were 511.5 N (SD, 81.9) in 1S1P50, 502.0 N (SD, 47.2) in 1S1P70, and 679.2 N (SD, 102.5) in 2S70. Maximum failure load was higher in 2S70 than in 1S1P70 (estimated difference, 176 N; Bonferroni-adjusted 98.3% CI, 31 to 301 N). Conclusions: Under static axial loading, 2S70 had a higher maximum failure load than 1S1P70, with no difference between 1S1P50 and either of the other 2 groups. Clinical Relevance: Under static axial loading, 2 HCSs had a higher maximum failure load than did 1 HCS with an antirotation pin at a 70° fracture angle in 3-D-printed canine femoral neck models.