Factors related to disagreement in implant size between preoperative CT-based planning and the actual implants used intraoperatively for total hip arthroplasty.

PURPOSE: In total hip arthroplasty, prediction of the optimal implant size is important in order to prevent perioperative complications. However, it is not easy to achieve complete agreement between the planned size and the actual size required appropriate implant fit. No previous report has adequately discussed the factors related to mismatch between predicted and actual implant sizes. The purpose was to report the results of a single surgeon case series of patients undergoing THA using computed tomography (CT)-based templating and the possible factors related to implant size mismatch.

METHODS: The study included 141 hips of 126 patients who underwent primary total hip arthroplasty with CT-based navigation. We retrospectively reviewed the planned and actual implant sizes used in these patients. Cup position, cup orientation and stem alignment were evaluated as surgical factors that could possibly be related to mismatch in implant size. Cortical index and canal flare index were also evaluated as morphological factors.

RESULTS: The final inclusions in this study were 124 hips of 111 patients including 82% of those were developmental dysplasia of the hip. Agreement in implant size was seen for 94.4% of cups and 85.5% of stems, respectively. No related factors were found for cup size mismatch. Stem alignment in the sagittal and coronal planes showed significant differences between the size-matched stem group and the smaller stem group ([Formula: see text]).

CONCLUSIONS: Implant size agreement rates between the three-dimensional plan and the actual implants used intraoperatively were high. However, broach alignment should be checked in the coronal and sagittal planes if the intraoperative broach is smaller than the planned size.