Statistical inference through AFT model for biotechnical systems

The objective of this paper is to model the phenomenon of degradation-to-failure for assemblies used for lumbar arthrodesis, starting from the analysis of their structure/geometry, the load applied and the kind of failure when several occur. An AFT model is proposed to model the joint effects of the applied load and the structural dimensions of the brand (namely length and diameter of the screw, presence of a connector or not) on the failure time due to a screw failure. The estimations of S–N curves and maximum permissible load (named critical load) values are provided as functions of the structural dimensions of the product. This allows comparisons of devices in terms of key factors determining product behavior and ageing under loading stress.