The Impact of Mixing Techniques on PMMA Bone Cement Subjected to Two Different Cooling Techniques: A Pilot Study of Thermal Management Strategies in Orthopedic Applications

Objectives: Polymethyl methacrylate (PMMA) bone cement is vital for prosthetic fixation in orthopedic surgery, yet its exothermic polymerization can exceed 80 °C, surpassing the 50 °C threshold for thermal osteonecrosis, risking implant failure. This pilot study assesses two cooling strategies—precooling cement components and saline irrigation on the polymerization temperature and compressive strength of antibiotic-loaded PMMA, comparing hand mixing (HM) and vacuum mixing (VM) to optimize thermal management while preserving mechanical integrity in controlled settings relevant to orthopedic applications. Methods: Antibiotic-loaded Simplex bone cement (Stryker, Kalamazoo, MI, USA) was prepared using HM and VM, per ISO 5833. Each batch was divided into three groups: control, precooled (components at 6 °C overnight), and saline irrigation (8 °C saline during setting). Each group included 20 cylindrical samples (1.5 cm × 3 cm), cured for 24 h. Core temperatures were monitored with embedded thermometers, and compressive strength was measured in megapascals (MPa) using a hydraulic press (C092-06, MATEST). Welch’s t-test was used for statistical analysis. Results: HM controls reached 76.2 °C, precooled 63.6 °C, and saline 66 °C; VM controls hit 71.8 °C, precooled 58.8 °C, and saline 63.6 °C. HM strengths were 16–17 MPa, with precooling reducing to 16.49 MPa (p = 0.051) and saline maintaining 17.07 MPa (p = 0.820). VM strengths were 76–80 MPa, with precooling at 78.45 MPa (p < 0.001) and saline at 76.77 MPa (p = 0.010). Failure modes varied: controls (uniform cracking), precooled (shear failure), and saline (mixed cracking/crumbling). Conclusions: Precooling significantly lowers temperatures but compromises strength in HM samples, limiting its use in load-bearing applications. Saline irrigation offers moderate thermal control while preserving mechanics, particularly in HM, suggesting a viable strategy for reducing thermal necrosis risk. VM ensures superior strength, supporting safe cooling application.