The term “extra vertebra” is most commonly used to describe an anatomical abnormality in which a person is born with six sacrum vertebrae in the spine instead of the more typical five. Medical experts estimate that this happens very rarely, usually in less than 4% of otherwise healthy live births, though it’s usually the case that it isn’t discovered right away. People who have this extra spinal section don’t usually have any visible physical problems, and some live their whole lives without ever noticing the addition. In others it can cause a lot of pain, though, which is typically how it is diagnosed.

The extra vertebra is a defect in the lumbar vertebrae region of the spinal cord - a person will have a sixth vertebra as opposed to the normal five.

Typical Human Spines

The human spine usually consists of 33 vertebrae, which are circular, collared bones that protect the spinal cord running through them. As humans become adults, five of the bones fuse together to form the sacrum or lumbar. The rest of the vertebrae are separate and individual bones. While an extra bone is not normal, it typically will not cause any pain in a patient unless it pushes on other body parts. Interestingly, research suggests that the lumbar regions of Homo erectus, some of the earliest humans, contained six vertebrae, too, though this is just one of many differences.

Vertebrae and the spinal cord.

Why Extra Bones Form

An extra vertebra is sometimes also called a “transitional vertebra” because it tends to develop at points where the spine transitions from one section to the next. For example, the bone may form at the point where the lumbar section of the spine connects with the sacrum section. Medical experts aren’t exactly sure why some people grow the additional bone, but it is usually something to do with genetic coding. The defect does tend to run in families, but not much is known about why some people are afflicted while others aren’t.

Research suggests that the lumbar regions of Homo erectus, one of the earliest humans, contained six vertebrae.

Consequences

It’s often the case that the sixth bone is significantly smaller than the other surrounding vertebrae. When this happens there aren’t usually any big consequences, at least not at first. Trouble is most common when the addition begins to grow, or when it causes the other bones to shift and rub against each other.

Health care professionals can usually identify an extra vertebra on X-rays of the spine.

Fully-formed extra vertebrae can cause chronic pain in the back and hips as a result of increased pressure. Crowding can move the spine out of alignment and push other bones, such as the hip and pelvis, out of place. Pain in other parts of the body is also common if nerve groups are affected. The spinal column is rich with nerves running to all parts of the body, and depending on where the addition is located, pain can be felt almost anywhere.

Detection and Diagnosis

Professional health care providers are usually able to identify an extra spinal bone through magnetic resonance imaging (MRI) scans or X-rays of the spine. It’s rare for a doctor to suspect an extra vertebrae right away, though, since other back problems tend to be much more common. Screens that turn up the extra bone are, in most cases, actually looking for something else.

Not all diagnoses are correct, either. Sometimes the first lumbar vertebra is not properly fused with the second, and this may cause a misdiagnosis of an extra vertebra. On the other hand, it is also possible for the extra bone to go undetected even after X-rays have been taken. Depending on the location and stage of development it may be hard to see during testing. Most experts recommend that people get a second opinion before proceeding with treatment.

Treatment and Lifestyle Changes

Treatment plans usually start gradually, and in most cases aim to restore the patient’s comfort. Actually curing the condition can be very difficult, since it’s not usually possible to remove a bone from the middle of the spinal column — at least not without being hugely invasive. Medication is commonly the first step, followed by physical treatment like stretching therapy and spinal injections designed to relieve pressure and diminish pain. Simple lifestyle changes like refraining from high-impact activities and sports may be recommended, too.

Surgery is sometimes suggested in extraordinary cases when the extra bone is causing debilitating distress or paralysis. Even in these instances, though, the procedure is typically designed more towards reliving pressure and restoring function than it is to actually offering a “cure.” If the vertebra does not cause discomfort or pain, however, there may be no treatment necessary. People commonly live full lives with this condition, and unless it is hampering the patient’s lifestyle there isn’t usually a need to change anything.