Abstract
We compare 2 methods (Ranawat's and Pierchon's) used to determine the centre of rotation of the hip, and attempt to establish which method calculates a position nearer to the real centre of rotation using informatics tools. We selected 17 patients with at least 1 healthy hip and made a pelvis anteroposterior X-ray. We obtained the image by picture archiving and communication systems (PACS) and applied the informatics tools provided by Alma IT Systems software. The centre of rotation of the healthy hip was determined and referenced to the teardrop image by vertical (A) and horizontal (C) distances. Then, both methods were applied to the same radiograph to determine which established a centre of rotation nearer to the anatomical centre identified. When the values for the healthy hip were compared with those obtained using Ranawat's method, highly significant differences were observed for both A (p<0.0001) and C (p<0.0001). When the results for the healthy hip were compared with the values obtained using Pierchon's method, neither the A (p=0.5258) nor the C values (p=0.3463) showed any significant differences. It would be advisable to use Pierchon's method to determine the centre of rotation during preoperative planning for a total hip arthroplasty when the anatomical alteration is bilateral.
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