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Pelvic tilt makes acetabular cup navigation inaccurate
Burkhard Lembeck1, Otto Mueller, Patrik Reize
1Department of Orthopaedic Surgery, University of Tuebingen, Germany. burkhard.lembeck@med.uni-tuebingen.de
Background:
Modern navigation techniques allow precise positioning of the acetabular cup relative to the anterior pelvic plane. Variations in pelvic tilt will affect the resulting spatial orientation of the cup.
Methods:
We measured pelvic tilt in 30 volunteers with an inclinometer combined with an ultrasonographic position measurement system. A mathematical algorithm was developed to calculate the resulting cup position measured on standard radiographs, depending on pelvic tilt.
Results:
Average pelvic tilt at rest was -4 degrees in the lying position and -8 degrees in the standing position, and ranged from -27 degrees to +3 degrees. Pelvic reclination of 1 degree will lead to functional anteversion of the cup of approximately 0.7 degree.
Interpretation:
Pelvic tilt makes navigation systems referring to the anterior plane inaccurate.
