The reconstruction of extended acetabular bone defects in revision hip arthroplasty - Risk factors for migration and loosening using the pedestal cup

Aim: For the reconstruction of extended acetabular bone defects in revision hip arthroplasty different implants and techniques are available. However, in cases with a broad operative range of new implants, specific indications must be determined. The aim of this study is to determine the risk factors for migration and loosening associated with implantation of the pedestal cup. Method: In a retrospective study the first 50 implantations of the pedestal cup in our hospital for high-grade acetabular defects (Paprosky classification II and III) were examined after a medium period of 26 months. Differences between radiologically loosened and osteal integrated implants in consideration of the preoperative osseous situation (defect size and morphology, bone density) as well as the implant positioning were determined as risk factors of an implant failure. Results: Three (6%) intraoperative implant-associated complications occurred, which were in the phase of the initial learning curve. In the early postoperative period 10 hip dislocations (20%) occurred. Two septic loosenings (4%) and 6 aseptic loosenings (12%) were observed. In 7 further cases a significant migration of the implant was assessed in the first months after surgery, a solid osteal integration did not appear. As risk factors for an implant loosening were determined: a missing reconstruction of the defect behind the pedestal cup with allogenous bone graft (p = 0.002), a lateralisation of the rotation centre (p = 0.023), the absence of the craniolateral wall (p = 0.002) and the presence of osteoporosis (p = 0.026). Conclusion: The pedestal cup is an implant that is well usable in many high-grade acetabular defect situations with good mid-term results; however, contraindications do exist. In cases with a significant osteoporosis, a missing sclerosis of the cranial acetabulum as well as extended damage of the lateral ilium and its absence, respectively, alternative procedures should be considered.