  Reproducibly achieving proper implant alignment is a critical step in total
hip arthroplasty (THA) procedures that has been shown to substantially affect
patient outcome. In current practice, correct alignment of the acetabular cup
is verified in C-arm X-ray images that are acquired in an anterior-posterior
(AP) view. Favorable surgical outcome is, therefore, heavily dependent on the
surgeon's experience in understanding the 3D orientation of a hemispheric
implant from 2D AP projection images. This work proposes an easy to use
intra-operative component planning system based on two C-arm X-ray images that
is combined with 3D augmented reality (AR) visualization that simplifies
impactor and cup placement according to the planning by providing a real-time
RGBD data overlay. We evaluate the feasibility of our system in a user study
comprising four orthopedic surgeons at the Johns Hopkins Hospital, and also
report errors in translation, anteversion, and abduction as low as 1.98 mm,
1.10 degrees, and 0.53 degrees, respectively. The promising performance of this
AR solution shows that deploying this system could eliminate the need for
excessive radiation, simplify the intervention, and enable reproducibly
accurate placement of acetabular implants.
