The Relationship Of The Abduction Angle And Anteversion Angle Of The Acetabular Cup With Dislocation After Total Hip Arthroplasty

Objective To study the relationship of the abduction angle and anteversion angle of the acetabular cup with dislocation after total hip arthroplasty. Exploring appropriate angle range of the abduction angle and anteversion angle of the acetabular cup,which provide theoretical basis for clinical practice.Methods From 2000 to 2010 ,30 patients (34 hips)were performed with total hip replacement in our hospital. Collect these cases as the research subject. There were 18 men and 12 women.The average age of the 30 patients in this series was 58 years(range,23～85 years). The preoperative diagnosis for each of the patients was osteoarthritis in 15 patients(17 hips),osteonecrosis in 8 patients (10 hips), femoral neck fracture in 5 patients (5 hips), ankylosing spondylitis in 2 patients(2hips).The standardized anteroposterior radiographs of the hip and the cross-table lateral film of the hip were used for measuring of the abduction angle and the anteversion angle.This study set abduction angle less than 50°and anteversion angle less than 20°as normal. The abduction angle was divided into two groups , one group was less or equal to 50°;another group was greater than 50°.The anteversion angle was also divided into two groups , one group was less or equal to 20°;another group was greater than 20°.The results were statistically analyzed ,with a P value less than 0.05 indicating significant difference.Results All the patients were followed up with an average of 20 months(range 3 months～30 months). Of the 30 patients(34 hips), there were 4 dislocations, the dislocation rate was 11.8%.All the hip dislocations occurred within the first 6 weeks after operation.And only posterior dislocation was occurred in this group. Recurrent dislocation occurred once in anthor one patient with 2 months after reduction.Closed reduction and the hip cast lasted 6 weeks were selected for all these patients,and all were successful.In the patients who had a dislocation , the average acetabular component abduction angle was 55.59°±5.87°, whereas the average abduction angle for the other patients who did not dislocate was 42.78°±3.87°. Two groups there were significant differences in the abduction angle(P<0.05).And the patients who had a dislocation ,the average anteversion angle was 25.64°±5.42°,whereas the average anteversion angle for the patients who did not dislocate was 14.60°±4.28°. Two groups there were significant differences in the anteversion angle (P<0.05).Abduction angle have significant differences in different range(≤50°,>50°) of dislocation rate(P < 0.05). Anteversion angle have significant differences in different range (≤20°,>20°)of dislocation rate (P<0.05).Conclusions1. The relationship of the abduction angle and anteversion angle of the acetabular cup with dislocation after total hip arthroplasty was closely related. It is of great significance for total hip replacement former planning, intraoperative and postoperative evaluation and rehabilitation guidance guide .2.We should try to avoid improper acetabular cup place in clinic. Keep abduction angle in 35°- 50°and the anteversion angle in 5°- 20°can provide a stable artificialhipjoint, and obviously decrease the incidence of postoperative dislocation.