Biomechanical criterion for selecting cancellous bone screws: arthrodesis in the hindfoot

The aim of the paper was to compare primary biomechanical stability of different arthrodesis screws (7.3 mm AO screw with and without washer, 6.5 mm Herbert screw and 6.5 mm Ideal Compression Screw (I.CO.S)). The work necessary to achieve an adequate compressive force with them was compared to the measurement with the AO screw with washer, because this method is for the time being the most commonly used one and is called the golden standard. Compressive force was measured indirectly, via screw tension measurement, with strain gauges method. From the measurements we calculated the work to reach a limit of 60 N and the ratios corresponding to the value of the golden standard: I.CO.S (35.2%), Herbert (89.0%), AO-screw without washer (116%). The I.CO.S showed superior results. Only in the case of extremely poor bone quality, a clear advantage of I.CO.S could be expected in practice.