Abstract
Background: The purpose of this prospective study was to asses the reliability of image-free navigated cup positioning and its correlation with biometrical parameters (age, sex, body mass index, soft tissue thickness overlying anterior superior iliac spine and symphysis pubis, and lumbar lordosis) and three different orientations of pelvis (tilt, obliquity, and rotation) in patients of Asian ethnicity.
Methods: Intraoperative data was obtained from 50 consecutive total hip arthroplasties in which acetabular cup implantation was done with a cementless cup (Plasma Cup SC®, Aesculap AG, Tuttlingen, Germany) using Orthopilot® image-free navigation system. The data was then compared with mathematically calculated synchronized anteversion and inclination obtained postoperatively through computed tomography and 3-dimensional processing.
Results: Mean navigated and synchronized inclination obtained were 40.1°±5.34° and 41.79°± 7.96° respectively (mean difference 1.69°±6.95°, range −20.72° ~ 18.47°), while the mean navigated and synchronized anteversion were 19.98°± 6.44° and 20.00°± 6.33° (mean difference 0.01°±6.35°, range −15.15° ~ 11.10°). A discrepancy of > 10° was observed in 5 hips in inclination and 5 hips in anteversion. No correlation was found between all of biometrical parameters and discrepancy of cup orientation. A statistically significant correlation was found between discrepancy of anteversion and pelvic tilt (1.78 + 0.55 x pelvic tilt°, r=0.493, p=0.0016).
Conclusion: In spite of variations in pelvic geometry, image-free navigation assisted acetabular cup positioning showed the significant reliability. The next generation of navigation systems must be combined with data on precision of pelvic orientation intraoperatively for complete validation.
*Index; Synchronized Inclination = arctan [tan (Operative AV) ÷ tan (Anatomic AV)] Synchronized AV = arctan[tan (Anatomic AV) x sin (synchronized Inclination)] or arctan[tan (Operative AV) x cos (Synchronized Inclination
Correspondence should be addressed to Diane Przepiorski at ISTA, PO Box 6564, Auburn, CA 95604, USA. Phone: +1 916-454-9884; Fax: +1 916-454-9882; E-mail: ista@pacbell.net
