Study Evaluates Alternate registration Planes for imageless,
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Imaginative computer navigation increases the precision of the component positioning in total hip arthroplastic (THA), although changes in the process are known to have an effect on final measurement accuracy. Investigators attempted to examine the precision of registration in the lateral decubitus position of an imageless navigation system during THA.

A prospective, observational study of 94 patients undergoing a primary THA with imageless navigation assistance was conducted. Patient position was registered using four planes of reference: the patient’s coronal plane (standard method), the long axis of the surgical table (longitudinal plane), the lumbosacral spine (lumbosacral plane), and plane intersecting the greater trochanter and glenoid fossa (hip-shoulder plane). Navigation measurements of cup position for each plane were compared to measurements from post-operative radiographs.

--Mean inclination from radiographs did not differ significantly from inclination using the coronal plane, the hip-shoulder plane or the longitudinal plane.

--Inclination measured using the lumbosacral plane differed significantly from radiographic measurements.

--Anteversion measured from radiographs did not differ significantly from the hip-shoulder plane.

--All other planes differed significantly from radiographs: coronal; lumbosacral & longitudinal.

In conclusion, the registration of patients with a plane approaching the long axis of the body provided a reference frame that assessed the cup position precisely. Registration using a hip-shoulder axis approximation plane; nonetheless, acetabular component position measurement was accurate and repeatable.