Osseointegration for transfemoral amputees: Influence of femur length and implant sizing on bone-implant contact and alignment.

Abstract

Clinical data on osseointegration (OI) for limb replacement indicates a concerning increase in mechanical complications after five years post-implantation. Since adequate bone-implant contact and proper implant alignment are critical factors for successful osseointegration, it is essential to identify the factors influencing these outcomes. This study aimed to assess the effects of residual femur length and implant sizing on bone-implant contact and implant alignment. Three-dimensional models of eight cadaveric femora were reconstructed from CT scans, and transfemoral amputations were simulated for each femur at three levels: short (ST: 1/3 L), medium (MD: 1/2 L), and long (LG: 2/3 L). Virtual OI surgeries were then performed using computer-aided design (CAD) models, and implant sizes were recorded. Subsequently, the effect of implant sizing was assessed by adjusting the implant size by ±1 mm. Contact length and implant alignment were compared between the groups using repeated measures analysis of variance with Bonferroni correction. The contact in the ST group (65.2 ± 7.3 %) was significantly less compared to the MD (96.1 ± 4.1 %, p < 0.001) and LG (96.8 ± 3.2 %, p < 0.001) groups. Upsizing increased contact in the ST group by 7.0 ± 2.6 % (p < 0.001), though it did not reach levels comparable to the MD and LG groups (p > 0.05). Additionally, sagittal implant misalignment was larger in the ST group (10.1 ± 2.0°) than in the MD (7.9 ± 1.5°) and LG (3.5 ± 1.6°) groups (p < 0.001), while no difference was observed in coronal implant alignment. These findings highlight the factors influencing mechanical complications of osseointegration implants and provide a basis for refined implant designs and surgical techniques for patients with short residual limbs.