Naohisa Miyakoshi, MD, PhD

The Spine Journal: Available online 3 October 2013

Abstract
Background Context
Sacral rib represents an uncommon pathology in which rib-like structures arise from the sacrum. Supernumerary ribs may occur at any level of the spine, but supernumerary ribs in the sacrococcygeal area are extremely rare.

Purpose
To present the case of a patient with sacral rib and to discuss this entity with reference to the literature.

Study Design
A case report and literature review.

Methods
A 17-year-old girl presented with low back pain and discomfort in bilateral gluteal regions. X-rays and computed tomography (CT) of the pelvis showed a smooth-surfaced, rod-like bony structure attaching to the sacrum on the left side. The appearance was consistent with sacral rib. The sacrum was hypoplastic and deviated to the right. Magnetic resonance imaging (MRI) showed insertion of the gluteus maximus (GM) onto the coccyx only on the right side. The sacral rib existed beneath the left GM muscle and received a partial insertion from the left GM muscle. No ligamentous continuation between the sacral rib and coccyx was observed.

Results
Conservative treatment relieved symptoms, so no surgical intervention was performed.

Conclusions
Sacral rib is a rare congenital anomaly for which surgical intervention is usually unnecessary. However, appropriate workups with CT and/or MRI should be considered for women, because sacral rib may cause complications during childbirth. In the literature, sacral/coccygeal rib is sometimes called “pelvic rib”. However, sacral/coccygeal rib should be distinguished from pelvic rib, because pelvic rib originating from the ilium is considered to represent a different entity.

Journal Website Abstract:  http://www.sciencedirect.com/science/article/pii/S1529943013015039