Too Much Variability Measuring Pelvic Obliquity

Did curve correction work in your patient with neuromuscular scoliosis? One way to know is via pelvic obliquity.

According to the authors of a new study, existing methods of measuring pelvic obliquity have resulted in “inconsistent values when used on the same radiograph.” The authors from Children’s Hospital at Montefiore, Bronx, New York, Children’s Hospital of Philadelphia, the University of Texas Health Sciences Center at San Antonio, and the Perelman School of Medicine at the University of Pennsylvania, Philadelphia designed and conducted a study which measured the degree to which potential differences between different five different measurement methods existed.

Their work, “The Variability of Pelvic Obliquity Measurements in Patients with Neuromuscular Scoliosis,” appears in January-March 2021 edition of The Journal of Bone and Joint Surgery Open Access.

“Correction of pelvic obliquity is key to determining success in the correction of neuromuscular scoliosis,” said co-author Keith Baldwin, M.D., M.S.P.T., M.P.H., associate professor in the the Department of Orthopaedic Surgery at Children’s Hospital of Philadelphia, to OTW. “Residual pelvic obliquity is associated with sitting imbalance, and pressure sores, particularly on the down side of the pelvis. As such assessment of pelvic obliquity is of paramount importance for assessing surgical success, but also for comparing techniques and assessment across large groups of patients.”

“In spite of this it is a little unclear how different studies approach this problem. There have been many other studies comparing reliability of various methods, the most cited of which was Wade Schrader’s paper. However, none before our work assessed the magnitude of potential difference between different methods of measurement. This is important because although there may be disagreement between methods, if the magnitude is small on average, it could be negligible.”

Using the Osebold, O’Brien, Allen and Ferguson, Lindseth, and Maloney techniques, five raters evaluated 63 patients with neuromuscular scoliosis, measuring their pelvic obliquity. The two groups were: coronal balance and coronal imbalance.

According to the authors, “The Maloney and Osebold techniques demonstrated excellent interrater reliability, and the Maloney, Osebold, and O’Brien techniques demonstrated excellent intrarater reliability. Significant differences in PO [pelvic obliquity] were found in 6 of the 10 comparisons for the balanced spines and 8 of the 10 comparisons for the unbalanced spines.”

As Dr. Baldwin explained to OTW, “We found that there was a larger difference between measurements when the spine is imbalanced (i.e., the head is not over the pelvis). As such the two major methods Osebold and Maloney can differ by quite a bit depending on spinal balance.”

“The work is important because large studies should report which method they use or risk comparing apples to oranges. I hope this study helps move surgeons towards a common language in assessing pelvic obliquity on studies of neuromuscular scoliosis.”