Sacral Obliquity, A Poorly Understood Congenital Anomaly

Introduction: Sacral obliquity, as defined by the Scoliosis Research Society Committee on Terminology three years ago, is an angular deviation of the sacrum from the horizontal line drawn parallel from a line across the femoral heads on an AP view of the sacrum. It is a distinctly separate entity from pelvic obliquity. Although much is understood about pelvic obliquity, little has been written about sacral obliquity’s diagnosis, presentation, or the magnitude of its affect on the more proximal levels of the spine.

Purpose: To establish sacral obliquity as a distinct abnormality, mostly congenital in origin and to demonstrate the method by which it is diagnosed.

Methods: Over the past 17 years, pelvic obliquity has been observed by the authors. Diagnosis was made on an AP x-ray of the sacrum (Ferguson) after a standing AP x-ray of the pelvis and spine showed level hips. The typical findings showed an asymmetrical elevation of the right sacral endplate, with no residual disc as would be expected with a hemivertabrae.

Results: We have found 63 patients with this distinct abnormality. One patient was found to have a traumatic origin. The remainder appear to have a congenital abnormality of varying degrees. The maximum amount of sacral obliquity identified was 20 degrees. In some cases, the sacral obliquity had little affect on the spine, but in others the obliquity appears to have potentiated a lumbar scoliosis of varying degrees with the maximum being 47 degrees.

Conclusion: Sacral obliquity has been found to be a separate and distinctly different entity from that of pelvic obliquity. Unlike pelvic obliquity, sacral obliquity is not easily discernable on an AP or PA scoliosis film, but requires a Ferguson view to appreciate the abnormality. Most cases appear to be congenital in origin with the sacral endplate elevated on the right side. One distinct case of traumatic origin has been identified. It is our opinion that the oblique take off of the lumbar spine secondary to sacral obliquity may function much like a hemivertebrae and affect the lumbar spine by creating, or potentiating a lumbar scoliosis. Failure to obtain the necessary radiographic views, may make it impossible to correct a lumbar scoliosis without developing residual coronal decompensation.