"Mechanical Integrity Assessment of Polymethylmethacrylate Bone Cement Incorporating Local Anesthetics: Implications for Joint Arthroplasty".

Background: Effective management of postsurgical pain following arthroplasty remains a challenge, lacking a definitive gold standard. As most knee and hip arthroplasties are cemented or hybrid, we used the property of bone cement as a drug carrier and added powdered local anesthetics (lidocaine hydrochloride and bupivacaine hydrochloride) to the polymethylmethacrylate (PMMA) as analgesics. However, the addition of drugs to bone cement may compromise its mechanical properties, necessitating a thorough analysis. Our objective was to assess the impact of added local anesthetics on the mechanical properties of PMMA bone cement.

Methods: Mechanical properties, including compressive strength, bending modulus, and bending strength, were evaluated following the procedure set by the International Organization for Standardization (ISO) 5833-2002 and the American Society for Testing and Materials (ASTM) F451-1 standards. There were three study groups compared: PMMA, PMMA with lidocaine hydrochloride, and PMMA with bupivacaine hydrochloride.

Results: Significant differences were observed between groups in compressive and bending strength, but not in bending modulus. Despite these differences, the mean compressive strength and bending modulus of all groups and the mean bending strength of the lidocaine group surpassed the minimum values set by the ISO 5833-2002 and ASTM F 451-08 standards for acrylic bone cement. However, the bupivacaine group fell short of the minimum bending strength value.

Conclusion: The addition of powdered local anesthetics to PMMA affects its mechanical properties, specifically compressive and bending strength, without compromising the bending modulus. While differences were noted, all groups surpassed the minimum standards for compressive strength and bending modulus. However, the bupivacaine group did not meet the minimum bending strength requirement. This highlights the importance of considering mechanical properties when incorporating drugs into bone cement for implant fixation.