Abstract
Purpose
The purpose of this study is to inspect balance of the pelvis in the acetabular operation of total hip arthroplasty (THA) using direct anterior approach (DAA), and it is to examine precision of the acetabular socket setting.
Materials and Methods
We performed THA using DAA to 104 patients (114 hips) joints from August 2006 to April 2009 and identified for seventy five patients (eighty four hips) that imaging of the postoperative CT was possible. The orientation of acetabular sockets were performed using an alignment guide which assumed an operating table an axis from August 2006 to September 2008 (A group), and using an alignment guide which assumed a pelvis an axis from October 2008 to May 2009(B group). A group were thirty eight patients (forty four hips), and B group were twenty eight (thirty). There were two men and thirty six women in A group, and one man and twenty seven women in B group. The average age of both groups was 66 years old. The objective angle of the acetabular socket was performed as angle guide of abduction of 45° and anteversion of 20°. The orientation of the acetabular socket converted the angle of postoperative CT into radiographic angle, and measured it. For sixteen hips in B group, both angle guide was used, and there were measured a difference of two angle guide in the acetabular operation as movement of the pelvis. The examination item assumed it the mean values of angle for the acetabular socket in both groups, precision to set up the acetabular socket to planned orientation within ±5 °and a mean difference of two angle guides of sixteen hips in B group.
Results
The mean values of abduction for the acetabular socket were 45 °in A group and 43.8 °in B group, and that of anteversion for the acetabular socket were 22.5 °in A group and were 20.9 °in B group. In A group, the precision to set up the acetabular socket to abduction 45±5 °was 91.8%, and that to anteversion 20±5 ° was 71%. Hips that anteversion of the acetabular socket was more than 25° were 13/44 joints. In B group, the precision to set up the acetabular socket to abduction of 45±5 °was 97%, and that to anteversion of 20±5°was 97.5%. The difference of two alignment guide for sixteen hips in B group were mean 5°(0～9°), and anteversion of pelvis decreased.
Disccussion
THA using DAA causes a pelvic anteversion during the acetabular preparation and as a result, anteversion of postoperative acetabular sockets increase. It suggests that even if DAA is supine position, the movement of the pelvis occurs.
Conclusion
The precision to set up the acetabular socket which we used alignment guide make the pelvis the axis was higher than that used alignment guide make the operating table the axis. In the acetabular preparation using DAA, anteversion of the pelvis occurred mean 5°.
