ObjectiveTo investigate the influence of the degree of acetabular deformity and the learning-curve on the acetabular cup positions in total hip arthroplasty (THA) for adults with developmental dysplasia of hip (DDH). MethodsBetween January 2008 and December 2015, 130 patients (144 hips) with DDH underwent primary THA, and the clinical data were analyzed retrospectively. Fifty-three patients (59 hips) were admitted before 2012, and 77 patients (85 hips) were treated after 2012. There were 32 males and 98 females, aged from 31 to 83 years (mean, 61). Unilateral replacement was performed in 116 cases and bilateral replacement in 14 cases. Of 144 hips, 48 hips were rated as Crowe type I, 57 hips as type II, and 39 hips as type of III/IV. The standard pelvic radiograph was taken within 1 week after operation. The mediCAD software was adopted to measure the angle of anteversion and abduction, bony coverage, and the distance between true rotating center and optimal rotating center to the connection of teardrops and the horizontal distance between two centers to evaluate the qualified rate of acetabular cup positions. ResultsCompared with the patients with the same type in 2013-2015 group, the anteversion angle and qualified rate of acetabular cup position significantly decreased in patients with Crowe I (P < 0.05); the horizontal distance significantly increased and qualified rate of acetabular cup position significantly decreased in patients with Crowe II (P < 0.05); and the anteversion angle significantly decreased and the horizontal distance significantly increased in patients with Crowe III/IV (P < 0.05) in 2008-2012 group. But no significant difference was shown in the other indexes (P > 0.05). In all Crowe types, the vertical distance between the true rotating center and the optimal rotating center increased with the degree of acetabular deformity in both 2008-2012 group and 2013-2015 group, showing significant difference (P < 0.05), but no significant difference was found in the other indexes (P > 0.05). ConclusionFor adults with acetabular dysplasia, there are high potential risks for unsatisfactory acetabular cup positions during primary THA. So it is necessary to evaluate acetabular deformities and to sum up operative experience so as to improve the accuracy of cups installation.