The frontal pelvic plane provides a valid reference system for implantation of the acetabular cup: spatial orientation of the pelvis in different positions.
BACKGROUND
The frontal pelvic plane has traditionally served as the reference plane for implantation of the acetabular cup during total hip arthroplasty, with referencing performed with the patient supine on the operating table. During daily activities in an upright position, the frontal pelvic plane changes from a horizontal to a vertical orientation. If this change in orientation is accompanied by a substantial change in pelvic inclination angle, it would mean that the use of the frontal pelvic plane as a reference plane for implantation of the acetabular cup would not be valid for proper alignment of the cup. To evaluate this possibility, we measured the change of inclination of the pelvis from the supine to the standing position.


METHODS
We evaluated 120 patients, first positioned in a standing position and then supine on a table. Three pelvic landmarks were digitized percutaneously, and the spatial coordinates were calculated with regard to pelvic orientation in the horizontal and the vertical plane.


RESULTS
We found a mean inclination of 6.7 degrees in the standing position and 5.6 degrees in the supine position. Patients who were more than 60 years of age who did not have coxarthrosis had a greater inclination angle (8.7 degrees ) while standing. Pelvic orientation was stable with regard to the supine and standing positions. These results were independent of sex, level of arthrosis, or status after implantation of a total hip replacement.


CONCLUSIONS
The frontal pelvic plane is a valid reference plane for implantation of the acetabular cup.
Department of Orthopaedic Surgery, Innsbruck Medical University, Austria. eckart.mayr@uibk.ac.at
Eckart
E
Mayr
Oliver
O
Kessler
Alexandra
A
Prassl
Franz
F
Rachbauer
Martin
M
Krismer
Michael
M
Nogler
D000077:Acetabulum / Q000502:physiology* / Q000601:surgery; D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D005260:Female; D006801:Humans; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery; D010384:Pelvic Bones / Q000502:physiology* / Q000601:surgery; D011187:Posture / Q000502:physiology*