[Radiological study on the cup abduction angle during total hip arthroplasty]

To analyze the relationship among the parameters by measuring the relevant parameters of the anteroposterior X-ray of both hips in patients after total hip arthroplasty, to discuss the reliable anatomical markers and reference standards of acetabulum placement in total hip arthroplasty, and finally to accurately control the abduction angle of acetabulum.

From January 2016 to June 2017, 282 patients (235 hips) underwent total hip arthroplasty and 128 patients(157 hips) met the inclusion criteria. There were 91 males and 37 females, 82 cases of the left hip and 75 cases of the right hip; ranging in age from 22 to 78 years old, with a mean of 55.1 years old. The abduction angle(β), ilium thickness (a), acetabular cup insertion depth (b), ischial thickness (c), acetabular cup insertion depth(d), acetabular abrasion and contusion depth(e) were measured on the postoperative AP X-ray of both hips, and the data were compared.

There was a positive correlation between β and b (r=0.424, P=0.000), a negative correlation between β and d (r=-0.407, P=0.000), a positive correlation between β and b/a (r=0.419, P=0.000), a negative correlation between β and d/c (r=-0.472, P=0.000). There was a linear relationship between β and b/a (t=5.753, P=0.000) and a linear relationship between β and d/c (t=-6.671, P=0.000).

The outreach angle is mainly controlled by the distance between the outer edge of the cup and the outer edge of the cup in the inferior portion(d) during the operation. The distance b from the outer edge of the cup can be used as a reference.