A Customized Knee Antibiotic-Loaded PMMA Spacer: A Preliminary Design Analysis

A preliminary design of customized antibiotic-loaded poly-methyl-methacrylate (ALPMMA) spacer characterized by an appropriate footprint according to the specific patient's anatomy and a reliable mechanical response to severe functional loads (i.e., level walking and 45° bent knee) is reported. The targeted virtual prototyping process takes origin from a novel patented 3D geometrical conceptualization characterized by added customization features and it is validated by a preliminary FEM-based analysis. Mechanical and thermomechanical properties of the antibiotic-doped orthopedic PMMA cement, which will be used for the future prototype manufacturing, were measured experimentally by testing samples taken during a real day-running orthopedic surgery and manufactured according to the surgeon protocol. FEM analysis results indicate that small area is subjected to intensive stresses, validating the proposed geometry from the mechanical point of view, under the two loading scenarios, moreover the value of safety margins results positive, and this is representative of the lower stress magnitude compared to the critical material limits. The experimental data confirm that the presence of antibiotic will last during the surgeon period moreover, the temperature dependent modulus of the bone cement is slightly affected by the body range temperature whereas it will drastically drop for higher temperature out the range of interest. A complete customization, according to a patient anatomy, and the corresponding real prototype spacer will be manufactured by 3D printing techniques, and it will be validated by destructive testing during the second stage of this activity before commercialization.