Pelvic Incidence in Patients with Hip Osteoarthritis

    Background: Hip osteoarthritis (OA) is a major cause of pain and disability that results in considerable social and medical costs. Mechanics such as posture, alignment and orientation of the hips and the spinal column and the relationship between these factors have been implicated in the development of both hip and spine pathologies. This study aims to test the hypothesis if pelvic incidence varies in patients with and without osteoarthritis. We assessed the relationship between spinopelvic alignment as measured by pelvic incidence (PI) and the presence of hip OA. Methods: We collected supine pelvis CT scans of ۱,۰۱۲ consecutive patients not known to have hip OA. Our first group consisted of ۹۵ patients with moderate to severe hip OA as per radiology reports. The second group included ۸۷ patients with no evidence of hip OA. Power analysis revealed the need for ۷۷ patients per group to find a mean difference in PI of ۵º or less between both groups. Two trained physicians independently measured the PI to account for inter-observer reliability. Results: Patients with moderate to severe hip OA had a mean PI of ۵۶.۵º±۱۲.۸º. The mean PI for patients without hip OA was ۵۷.۲º±۷.۵º. An independent samples t-test revealed no significant difference between the PI values of the two groups. Spearman’s correlation coefficient of ۰.۷۵۴ demonstrated a high inter-observer reliability. Conclusion: There was no difference in PI angle of hip OA patients and "healthy" patients. Our measurements of patients without OA were almost identical to the reported normal PI values in the literature. It appears that hip OA is not associated with PI angle, refuting the hypothesis made in previous studies, stating that elevated PI contributes to the future development of hip arthritis. CT scan seems to be a reliable and accurate way of assessing pelvic incidence.      

Keywords:

Hip osteoarthritis , Hip-Spine syndrome , Pelvic incidence