RESUMO
PURPOSE: New repair techniques for fragility fractures such as those of the distal radius require biomechanical justification. This study was conducted to investigate a technique using an expanding polymer bone cement to provide strength to a fracture repair. METHODS: Distal and proximal ends were isolated from 6 pairs of human radii (mean age 65). Transverse osteotomies were made near the head of each specimen. Paired specimens were repaired using 2 materials of differing polymer chemistries: polyurethane versus polymethylmethacrylate. Repaired specimens were subjected to failure tests in a cantilever beam configuration (distal, n = 6 per treatment) or pure tension (proximal, n = 5 per treatment). Cement penetration tests were conducted using a uniform open-cell model of cancellous bone. Baseline mechanical properties of the polyurethane cement were determined according to ASTM standards. RESULTS: Distal radii repaired with polyurethane bone cement withstood average shear stress 2.9 times as high as polymethylmethacrylate (0.91 vs 0.31 MPa). Peak tensile bending stress was 2.5 times as high in polyurethane (2.57 vs 1.02 MPa). Under pure tension, polyurethane-repaired samples failed at 0.83 MPa versus 0.74 MPa for polymethylmethacrylate. The polyurethane cement expanded to penetrate 49% farther into the trabeculae. The polyurethane cement had mean compressive yield stress of 20.3 MPa, compressive modulus of 754 MPa, ultimate tensile stress of 18.5 MPa, and tensile elastic modulus of 723 MPa. CONCLUSIONS: The biomechanical strength data indicate the potential of an expanding bone cement as a candidate strategy for fracture repair. Further evaluation might provide evidence for such an alternative repair strategy for fragility fractures, including those of the distal radius.
