Introduction
Evidence & Methods
Transitional vertebrae are common and have surgical implications. This study assesses their prevalence detected on abdominal films in 1,100 United States subjects.
Approximately one-third of subjects studied were found to have transitional vertebrae of various configurations. In more than 5%, the number of lumbar levels was only 4. Approximately 15% of the subjects had nonmobile or minimally-mobile caudal segments.
The presence of transitional vertebrae can impact identification of intraoperative levels (McCulloch's “most common cause of wrong-level surgery”), clinical findings (prefixed versus postfixed lumbosacral plexus), and the anterior approach (a shift in the level of bifurcation). This study confirms previous reports on the diversity of native anatomy and potential for erroneous surgical planning or execution.
—The Editors
The vertebral column supports the weight and burdens of the upper body. This weight subjects the spine to an increasing magnitude of vertical compression forces, transmitted axially toward the lumbosacral joint. At this point, the transference of most forces occurs between L5–S1 vertebral bodies and the articular facets; it then extends horizontally via the ligaments to the sacrum, then downward to the lower extremities [1]. Whenever anomalous articular facets are present between L5–S1, load can be conveyed from the L5 transverse processes (TPS) through the iliolumbar ligaments [2].
Lumbosacral transitional vertebra (LSTV) is a congenital vertebral anomaly of the L5–S1 junction in the spine. Definite manifestations are lumbarization of S1 (nonfusion between the first two sacral segments) or sacralization of the fifth lumbar vertebra (fusion between L5 and the first sacral segment). This alteration may contribute to incorrect identification of a vertebral segment, which can lead to spine surgery at the wrong level and unresolved symptoms [3]. Interestingly, McCulloch and Waddell [4] showed that the L5 nerve always originates in the “last mobile” segment of the spine, and Hughes and Saifuddin [5] reported nearly a 70% absence of the iliolumbar ligaments in subjects with lumbosacral transitional segments, confirming that presence of a transitional state disrupts normal spinal biomechanics and anatomy.
Kidney-urinary bladder or abdominal radiographs have many clinical uses and are most often indicated for patients who exhibit signs of intestinal obstruction or visceral perforation. They can also be used to verify the placement of nasogastric feeding tubes and assess the urinary system. This study uses abdominal radiographs for a different purpose, that is, to provide a radiographic image of the lumbar spine, especially our area of interest, L5–S1. Given the vast range of purposes for which abdominal radiographs are obtained, the images from a radiographic study initially performed for abdominal indications would provide a diverse sample that represents the general population and therefore be appropriate for a study that evaluates subjects for LSTVs.
Several studies describe the occurrence of this anomaly in a back pain population [6], [7], [8], [9], [10], [11]; however, investigation of the prevalence in the American general population is lacking. Therefore, our study aims to establish the prevalence rates for LSTVs in the American general population, with the hypothesis that it will be lower than the back pain–associated prevalence reported in the literature.