A high risk of postoperative periprosthetic femoral fracture in Dorr type C femurs: a retrospective cohort study with ten-year follow-up data and a preliminary monochromatic image analysis

We applied Anatomique Benoist Girard II (ABG II) stems for total hip arthroplasty (THA) in some Dorr type C femurs as early attempts. Here, we compared the long-term follow-up results between ABG II stems and the "well-performing" Corail stems and their monochromatic images.Among 3214 primary THA records, 43 short ABG II stems and 67 standard-length Corail stems implanted in Dorr type C femurs were eligible and enrolled in this retrospective cohort study, with a mean follow-up of 10.3 years. Revision rates, Harris hip scores, and radiologic signs were compared. Spectral CT scans from a representative sample were obtained, and monochromatic images were reconstructed. A quantitative method was developed to measure the volume of the gap around stems. Patient-specific finite element analysis was conducted to investigate the strains.The revision rate of ABG II stems was significantly higher than that of Corail stems (21% vs. 3%, P<0.05). In the monochromatic images, fewer spot-weld signs (2.15 vs. 3.38, P<0.05) and wider gaps around stems (1.64 cm3 vs. 0.13 cm3, P<0.05) were observed on average in the ABG II group. The mean maximum principal strains of the proximal femurs in the ABG II group were close to the yield strains and significantly larger than those in the Corail group (0.0052 vs. 0.0011, P<0.05).There was a high risk of postoperative periprosthetic femoral fracture for ABG II stems in Dorr type C femurs. Monochromatic images provided some insight into the failure mechanism.III.