Individual bone cement spacers (IBCS) for septic hip revision - preliminary report

Background: Two-stage septic hip revision with intermediate resection arthroplasty leads to temporary poor function and difficult reimplantation. Antibiotic-loaded cement spacers improve patient mobility and maintain stability of the joint as well as length of the limb. Prefabricated spacers are readily available but lack adaptability. We developed modular moulds separately for stem and head to create more individual spacers with optimised femoral press-fit and smooth head surface. Methods: Moulds are fabricated preoperatively by forming 4 mm polyethylene over trial stems and cups under vacuum (MS 30, Center-pulse, Switzerland). After gas sterilization, Refobacin Palacos (Merck, Darmstadt, Germany) is poured into stem and head moulds of appropriate size. A double K-wire is inserted as a rod. Fluoroscopy is used to check for air inclusions, which might impair resistance. For mechanical resistance testing trials, 5 spacers were resin-fixed with 80% stem insertion and loaded in a craniocaudal direction at 20 N/s (universal testing machine, Zwick, Germany) until failure. Results: The static testing showed an average failure load of 1550 N (range 1350-2000 N). The K-wires prevented complete dislocation of the fragments. Conclusion: Partial weight-bearing is possible with this system, but a fall might lead to an acute fracture. New materials for the core can be tested with our biomechanical model. Following the presented craniocaudal static testing, torsion testing and dynamic testing in Ringer's solution are planned.