Analysis of the micro-migration of sliding hip screws by using point-based registration

Purpose The favored treatment for many hip fractures is a sliding hip screw, and its usage is expected to increase in the future. Failures can be reduced, and complications detected earlier by semi-automated CT image analysis. The most frequent failure is due to the screw cut-out from the femoral head. Methods An image-based method was developed for early detection of complications and assessment of anchorage quality relative to implant model, bone quality or tip-apex distance (TAD). This method evaluates micro-migration using CT images acquired at different time points (immediately post-op and 3-month later). Serial CT image registration and transformation methods were applied, including point-based registration, to achieve semi-automated evaluations. Results Qualitative and quantitative validation of the image registration was performed with measurement mean error determination by different observers. The micro-migration evaluation by clinicians compared favorably with semi-automated image-based results. Conclusion Semi-automatic evaluation of hip screw micro-migration using CT images is feasible and can aid observation of convalescence. The method may be amenable to full automation, a future goal for this work.