The human spine has five vertebrae in the lumbar region, often referred to as the lower back. Anatomical variations are common and usually do not cause issues. One such variation is the presence of a sixth lumbar vertebra, also known as a transitional vertebra or lumbarization of S1.
Understanding the 6th Lumbar Vertebra
A 6th lumbar vertebra is a developmental variation where the spine at the lumbosacral junction deviates from the typical five lumbar segments. This can occur in two ways. The first sacral vertebra (S1), normally fused with the sacrum, develops characteristics more akin to a lumbar vertebra and remains unfused. This is termed “lumbarization of S1.”
Alternatively, an individual may have an additional lumbar-like vertebra situated above the sacrum. This anatomical difference is congenital, forming during fetal development, and affecting how the lumbar spine connects with the sacrum.
Prevalence and Occurrence
The presence of a 6th lumbar vertebra is a common spinal anatomical variation. Some reports indicate a prevalence ranging from approximately 1% to 5% of individuals. Broader categories of lumbosacral transitional vertebrae (LSTV), which include the 6th lumbar vertebra, show wider ranges, sometimes reported between 2.6% and 35.6%.
Other studies suggest an additional lumbar vertebra might be present in around 10% of adults. Lumbarization of S1 has been reported with a prevalence between 3% and 7%. Many individuals with this variation are unaware of its presence and live without symptoms.
Clinical Considerations and Potential Symptoms
While a 6th lumbar vertebra is often asymptomatic, it can sometimes be associated with certain spinal conditions. Individuals with this variation may experience low back pain, disc issues, or nerve compression. Symptoms arise from altered biomechanics and increased stress on adjacent spinal segments.
An extra vertebra can modify the distribution of weight and forces across the lower spine, potentially leading to increased strain on intervertebral discs or changes in spinal flexibility. This can contribute to conditions such as disc herniation or nerve impingement, like sciatica. However, many individuals with a 6th lumbar vertebra experience no related health problems.
Identification and Care Approaches
A 6th lumbar vertebra is typically identified incidentally during imaging studies for other reasons, such as investigating back pain. X-rays, CT scans, or MRI scans are diagnostic tools that show the number and morphology of the vertebrae. These allow medical professionals to accurately count spinal segments and identify structural variations.
If symptoms are present, care approaches usually involve conservative management strategies similar to those for other forms of low back pain. This includes physical therapy to strengthen muscles and improve flexibility, and pain relief medications. Injections may also be considered to alleviate inflammation and discomfort. For asymptomatic individuals, no specific treatment is required.