Significance of Ranawat''s triangle method in determining the rotation center of normal hip joint / 中国组织工程研究

ABSTRACT

BACKGROUND:It is crucial to determine the location of the rotation center of the hip joint using X-ray.Ranawat's triangle is commonly used to define the hip rotational center in bilateral developmental dysplasia of the hip and revision hip surgery especialy in cases with bone stock deficiency,but there are rare articles about its value in normal hip.OBJECTIVE:To compare the difference between Ranawat's triangle method and Mose circle method in determining the healthy hip joint rotational center.METHODS: We selected 30 patients with normal traumatic femoral neck fracture,who underwent unilateral total hip arthroplasty.Ranawat's triangle method and Mose circle method were applied to measure the anteroposterior radiographs of the pelvis after arthroplasty and to compare the distance between the hip rotational center and the reference lines (X-axis teardrop line; Y-axis a line perpendicular to the X-axis,drawn from the intersection of theKohler line and the teardrop line.The distance from the hip joint rotational center to X-axis is dx1,dx2 and the distance to Y-axis is dy1,dy2 in Ranawat's triangle and Mose circle respectively.).We also compared the ratios (dx1/H,dy1/W; dx2/H,dy2/W) in the pelvic height (H the distance between the highest point on the iliac wing and the lowest point on the ischial tuberosity) and width (W the distance between the most lateral points on the iliac crests).RESULTS AND CONCLUSION:When the values were compared with both methods,highly significant differences were observed for both X and Y,Ranawat's triangle method dx1=(19.52±3.03) mm,dy1=(24.43±2.26) mm; and Mose circle method dx2=(11.90±3.55) mm,dy2=(34.29±3.79) mm (P＜0.001) and these ratios (dx1/H=0.0992±0.0133,dy1/W=0.0855±0.0069; dx2/H=0.0611±0.0194,dy2/W=0.1201±0.0178) in pelvic height and width (P＜ 0.001).Scatterplot results demonstrated that the hip rotational center identified by Ranawat's triangle method is near to the proximal end and medial end,which may affect mechanical environment surrounding the joint.For cases of bilateral hip dysplasia and joint revision,because of the changes in structure surrounding the acetabulum,Ranawat's triangle method can be a feasible method to identify the hip rotational center.For cases of unilateral lesion,Mose circle method can exactly identify the hip rotational center taking healthy side as a control.