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Changes of center of rotation and femoral offset in total hip arthroplasty.

BACKGROUND
It is a challenge to reconstruct the center of rotation (COR) and femoroacetabular offset anatomically in total hip arthroplasty (THA). We addressed the controversy how we manage to preserve the COR and femoroacetabular offset with an uncemented total hip prosthesis implanted with free hand technique.


METHODS
We analyzed a prospective series of 73 patients who underwent primary THA. The series was composed of 40 females and 33 males, mean age 64 years (range, 35-90 years). The reasons for THA were primary osteoarthritis (n=63) and developmental dysplasia of the hip (n=10). Pre- and postoperative X-rays were done in a standardized format for anterior-posterior (AP) radiographs of the pelvis, and digitalized measurements were done using SectraTM. We compared preoperative measurements with the final outcome to determine changes in COR and femoral offset.


RESULTS
We found that 40 patients had their COR and 34 patients had their femoral offset preserved within preoperative 5.0 mm limits. Twenty-three patients had both their values of COR and femoral offset preserved within 5.0 mm limits. While a significant correlation was found between changes of femoral and global offset (r=0.786, P<0.001), there were no correlation between changes of acetabular and femoral offset (r=-0.027, P=0.822).


CONCLUSIONS
Using an uncemented THA and free hand technique, there is a fair reproducibility of anatomy. The variations were mostly minor, but our results indicate a potential for better restoring the location of COR and femoral offset when planning and implanting an uncemented THA.