Postoperative impacts of reamer-irrigator-aspirator (RIA) on femoral strength: A finite element analysis

The reamer-irrigator-aspirator (RIA) system is used to harvest a large amount of autologous bone graft, most commonly from the femur. One of its major complications is postoperative fracture resulting from decreased bone strength. Although the number of reported cases is limited, it is a serious issue because it involves fracture in originally healthy bone. While several cadaveric studies have examined post-RIA bone strength, no studies have investigated it using finite element analysis (FEA). The aim of this study was to elucidate the effects of RIA on postoperative femoral strength using FEA.

Quantitative computed tomography (CT)-based FEA was performed using pre- and postoperative CT images from three patients who underwent RIA of the entire femur for autologous bone grafting during nonunion surgery at our institution. Patient 1: a 60-year-old man who underwent reaming with a reamer 4 mm larger than his isthmus diameter. Patient 2: a 71-year-old woman with a wide endosteal diameter, typical of osteoporotic bone. Patient 3: a 64-year-old woman with cortical penetration on the posterior proximal diaphysis and the anterior supracondylar region. Three loading conditions were analyzed for each patient: (a) axial loading, (b) direct force, and (c) rotation. Fracture load was defined as the minimum load at which at least one shell element failed at the complete fracture site. Fracture sites and fracture loads were compared between the pre- and post-RIA models.

In Patients 1 and 2, the decrease in femoral strength after RIA was limited, and fracture sites remained unchanged between the pre- and post-RIA models. In contrast, in Patient 3, who had cortical penetrations after RIA, fractures occurred at the penetration sites under rotational loading, with 78% lower fracture load than before RIA.

The postoperative reduction in biomechanical femoral strength under axial loading, direct force, and rotational loading conditions was minimal in cases without cortical penetration. However, in the penetration model after RIA, fractures occurred at the penetration sites under rotational loading with markedly lower torque. These findings may provide insights for postoperative rehabilitation strategies and for evaluating fracture risk, which represents the most severe complication after RIA.