Accuracy of Acetabular Cup Placement in Navigated THA with Modified Registration Technique in Semilateral Decubitus Position
Yingyong Suksathien MD*, Rachawan Suksathien MD**, Porameth Chaiwirattana MD*
Affiliation : * Department of Orthopedic Surgery, Maharat Nakhon Ratchasima Hospital, Thailand ** Department of Rehabilitation Medicine, Maharat Nakhon Ratchasima Hospital, Thailand
Background : The accuracy of cup placement in navigated total hip arthroplasty (THA) depends on the bony landmark
registration intraoperatively. We created a semilateral decubitus position that combined the advantage of supine position
for registration and lateral decubitus position for better femoral canal visualization.
Objective : To evaluate the accuracy of cup placement within the “safe zone” and of imageless navigation measurement by
comparing the intraoperative values of acetabular cup abduction and anteversion to postoperative CT values.
Material and Method: All cases were performed in semilateral decubitus position with OrthoPilot THA plus 3.2 (cup only)
software (Aesculap AG). Postoperatively, a multislice computed tomographic (CT) scan was obtained at two months or
later for abduction and anteversion angle measurement. The abduction and anteversion angle measured on postoperative
CT were compared to the intraoperative measurement with a paired t-test and a correlation test at a 0.05 level of significance.
Results : Sixty-five cases were included in the present study. The median CT abduction value was 41°, range 35° to 48° and
the median navigated abduction value was 39.8°, range 37.5° to 45.5°. The median paired difference was 1.6°, range -3.4°
to 7.9°, this difference was significant (p<0.001). The median CT anteversion value was 15°, range 8° to 28° and the median
navigated anteversion value was 12°, range 5.9° to 16.5°. The mean paired difference was 3.2°, range -2.6° to 14.9°, this
difference was significant (p<0.0001).
Conclusion : Navigated THA with modified registration technique in semilateral decubitus position offered a more precise
cup position as in supine and lateral decubitus position. It combined the advantage of supine position for registration and
lateral decubitus position for better femoral canal visualization. Our modified registration technique by compressing the
soft tissue above pubic symphysis (PS) to the abdomen and registering at the antero-superior-pubic-symphysis (ASPS) help
us to increase the accuracy of anteversion angle.
Keywords : Hip arthroplasty, Imageless navigation
