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Is Ranawat triangle method accurate in estimating hip joint center in Japanese population?
Masanori Fujii1, Tetsuro Nakamura2, Toshihiko Hara3
1Department of Orthopaedic Surgery, Japan Community Health Care Organization (JCHO) Kyushu Hospital, 1-8-1 Kishinoura, Yahatanishi-ku, Kitakyushu 806-8501, Japan; Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi. Higashi-ku, Fukuoka 812-8582, Japan.
Background:
Little information has been available regarding the usefulness of Ranawat triangle method in estimating anatomical hip joint center in the Japanese population. In this study, we aimed to determine the accuracy of the method in estimating hip joint center.
Methods:
Using digitally reconstructed radiographs of 123 normal hips (123 patients), we measured the hip joint center coordinates (Cx, Cy) with reference to the ipsilateral lowest point of the teardrop, the pelvic width, and the pelvic height. Using these measurement values, we performed the following analyses: (1) the relationship of hip joint center location with pelvic dimensions; (2) accuracy of Ranawat method in estimating hip joint center; (3) alternative methods to estimate hip joint center using pelvic height.
Results:
The mean Cx and Cy were 32 ± 3.0 mm and 13 ± 2.1 mm, respectively. Pelvic height was positively correlated with Cx (r = 0.51, p < 0.001) and Cy (r = 0.69, p < 0.001), but the correlations of pelvic width with Cx and Cy were negligible. The mean estimation error of the Ranawat method was -6.7 ± 2.6 mm in x-axis and 6.6 ± 1.9 mm in y-axis, respectively. The hip joint center was estimated within a 5 mm error in both axes in only 8 hips (6.5%). Thus, we developed two estimating methods using pelvic height, modified Ranawat method and pelvic height ratio method, and the estimation errors of these methods were within 5 mm in both axes in 118 hips (96%) and 116 hips (94%), respectively.
Conclusions:
Ranawat method showed poor accuracy in estimating anatomical hip joint center and is not recommended for clinical use. Our alternative methods may be useful for surgeons planning the position of the acetabular component in total hip arthroplasty.
