Biomechanical evaluation of the cup-on-cup technique for Paprosky IIIB acetabular defects: a finite element comparison of revision hip surgery strategies

• To establish a 3D finite element model of the cup-on-cup, jumbo cup, hip revision with one TA and hip revision with two TAs to simulate the hip revision realistic application scenarios. • Provided important references and surgical selection strategies for the treatment of severe Paprosky IIIB acetabular defects. • Jumbo cup surgery results in higher stress in cancellous bone and acetabular cups compared with the cup-on-cup technology and TA. TA has disadvantages in postoperative Implants displacement, compared with the cup-on-cup technology. • The cup-on-cup technology showed significant advantages in stress distribution and displacement, offering a novel solution and important references for revision surgery in Paprosky IIIB acetabular defects. This finite element analysis study biomechanically evaluated the cup-on-cup technique against jumbo cup and trabecular metal augment (TA) in Paprosky IIIB acetabular defects to assess its application value. The biomechanical feasibility and clinical potential of the cup-on-cup technique were evaluated. A pelvic model was developed from CT scans, and the Paprosky IIIB acetabular defect was created. Simulations of the four techniques were performed, analyzing von Mises stress and displacement under static loading. Among the four types of surgical techniques, there was almost no difference in cortical bone stress when standing, walking, or jogging. Under the four types of surgical techniques, the peak stresses of cancellous bone were 0.355, 2.921, 1.054, and 1.123 MPa during standing, respectively; the peak stresses were 2.136, 3.257, 2.721, and 2.684 MPa during walking, respectively; and the peak stresses were 4.989, 6.387, 4.862, and 4.747 MPa during jogging, respectively. The stress on the acetabular cup was still highest after the jumbo cup, with values of 9.02, 36.64, and 83.49 MPa at 210, 2100, and 4200 N, respectively. There is no difference in acetabular cup stress between cup-on-cup surgery and hip revision with TA. When standing, the stress on the lateral cup after cup-on-cup surgery was minimal, while the stress on the lateral cup after cup-on-cup surgery was greater during walking and jogging. After the cup-on-cup technique, the displacement of the acetabular cup during standing, walking, and jogging is 0.0426 mm, 0.3769 mm, and 0.7053 mm, and the displacement of the lateral cup during standing, walking, and jogging is 0.0365 mm, 0.3278 mm, and 0.6157 mm. Among the four hip revision surgeries, only the cup-on-cup technique had the smallest displacement and maintained good immediate postoperative stability. In summary, these findings not only reveal the differences in mechanical behavior and potential advantages and disadvantages of different techniques. At the same time, it also demonstrated that the cup-on-cup technology provides a promising solution for Paprosky IIIB acetabular defects while protecting the host bone and enhancing biomechanical stability.