How accurately pre-operative planning matches the achieved surgery: a finite element study.

Pre-operative planning trains the surgeon in the workshop environment. The final objective of the early researches along this line is to arrange a set of instruments to predict the primary stability in the pre-operative planning moving toward a less and minimally invasive surgical technique. Nevetheless, even assuming a perfect surgical planning, there is still the practical problem of correct positioning of the stem in the femur during surgery. An erroneous initial positioning could lead to the implant instability promoting the ultimate failure of the implant [1,2]. Initial excessive relative micromotions at the bone-implant interface may inhibit the bony in-growth and secondary long term fixation [3,4]. To achieve a good level of primary stability the surgery technique play therefore a fundamental role. Aim of the present study was to asses the sensitivity of the relative bone-implant micromotions, stresses and strains to the surgical parameters as planned and achieved by the surgeon respectively before and after the operation. For this purpose, the subject-specific finite element (FE) model of a cadaveric femur, accounting for patient and surgeon, was derived from pre-operative and post-operative CT scans. The specific aim was to verify if finite element models based on pre-clinical planning correctly match the achieved implant stability conditions.