A novel patient-specific free-hand method using fluoroscopic templating for accurate cup placement in supine position total hip arthroplasty

Introduction

We developed a fluoroscopic templating technique for accurate cup placement based on the acetabular morphology of individual patients during supine position total hip arthroplasty (THA) to reduce the risk of dislocation. This study aimed to evaluate cup positioning accuracy with and without this technique.

Materials and methods

We evaluated 75 consecutive hips of 70 patients undergoing cementless anterolateral supine THA. The target angle for radiographic inclination (RI) and radiographic anteversion (RA) were set using a computed tomography (CT)-based functional pelvic plane. In 25 hips, we implanted the cup using a mechanical alignment guide (C-group). A fluoroscopic templating technique was used in 50 hips (FT-group), and a reference line based on the acetabular morphology was preoperatively set in each patient for the RI guide. A reference diagram was made for the RA guide. Postoperative CT scans were used to compare cup positioning accuracy between groups.

Results

The absolute values of the error from the target angle were 3.2 ± 2.0° (RI) and 6.5 ± 3.8° (RA) in the C-group, and 1.5 ± 1.2° (RI) and 2.6 ± 1.9° (RA) in the FT-group. The errors of both RI and RA were significantly smaller in the FT-group than in the C-group. The rates of cases within ± 5° of the target angles for both RI and RA were 48% (C-group) and 92% (FT-group). The mean fluoroscopic times were 32.2 s (C-group) and 17.4 s (FT-group).

Conclusion

Our simple patient-specific technique achieved accurate cup positioning; this may reduce the risk of dislocation.