Calcium phosphate cement composites in revision hip replacement

Loosening and failure of hip implants can cause extensive bone loss, and revision of the implant can pose a challenge to the surgeon. Impaction allografting has gained popularity as a method to treat the bone loss. However, significant rates of complications have been seen, including massive subsidence of the implant and perioperative fractures. Subsidence may be due to graft layer consolidation or failure. It is hypothesized that the addition of an interstitial, resorbable cement may improve the clinical outcome of this procedure while reducing the impaction forces and simplifying the surgery. The goal of this thesis was to evaluate the handling characteristics and mechanical properties of a bone particle-cement composite material. Mixtures of bone particles with a commercially-available calcium phosphate cement were made with 25% to 100% cement by volume. Viscosity of the composite paste was tested in a capillary rheometer to quantify the handling characteristics, and compared to PMMA. Composite cylindrical specimens were moulded and set for 24 hours in a 37°C water bath. Specimens were tested in uniaxial compression, diametral tension and shear. The composites were also tested in confined compression along with 100% bone specimens. The viscosity of pure cement paste was similar to PMMA, but showed a large increase due to the addition of bone particles. The paste did not flow at bone fractions higher than 25%, so the surgical procedure for these compositions may require hand packing. Compressive and tensile ultimate strengths were 1.35-2.47MPa and 0.25-0.67MPa, respectively. Compressive modulus increased from 15MPa for 75% bone specimens to 270MPa for 100% cement specimens. There was an associated large decrease in ductility. The confined compression modulus was 6MPa for bone particles and 50MPa for 25%o cement. Above 25% cement, the modulus ranged from 163 to 316 MPa. The composite material showed improved strength and stiffness compared to bone particles alone. Further testing is required with more realistic loading models as well as assessment of the biological characteristics, however results indicate the composite material may be appropriate for use in treating extensive bone loss in revision hip arthroplasty.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat