Mechanical strength of poly(methyl methacrylate) cement-human bone interfaces.

A device was constructed to test the interfacial strength of PMMA-based bone cement and human cancellous bone under pure tension. Two types of tissue were used in the investigation: (1) formalin-fixed vertebral bone as an in vitro model for weak cancellous bone, and (2) freshly removed metatarsal bone. Tissue--cement joints were allowed to solidify under two different pressures (0.11 and 0.47 MPa), and cement placement time on tissue surfaces was also controlled as a variable. The higher curing pressure only seemed to enhance the strength of interfaces formed with mechanically weak fixed bone but had no significant effect for joints formed with the stronger, freshly extracted tissue. Cement placement time did not have a discernible effect on interfacial strength regardless of the tissue used or the pressure applied during setting. An analysis of fracture morphology by optical microscopy revealed largely cement cohesive failure in some cases and bone or mixed fractures in others. Joints exhibiting mainly cement fracture had the highest interfacial tensile strengths (in the order of 7.5 MPa). Once measured values of tissue porosity were taken into account, the observed joint strength correlated well with cement tensile strength. Based on experimental findings, better stress-dissipating qualities and higher tensile strength are suggested as two important necessary improvements of bone cements based on poly(methyl methacrylate).