Sacralization is a common irregularity of the spine, where the fifth vertebra is fused to the sacrum bone at the bottom of the spine. The fifth lumbar vertebra, known as L5, may fuse fully or partially on either side of the sacrum, or on both sides. Sacralization is a congenital anomaly that occurs in the embryo.

Sacralization often has no symptoms. It’s sometimes is associated with lower back pain or problems with posture and movement. It’s also called lumbosacral transitional vertebrae or LSTV.

The extent and type of sacralization varies widely from individual to individual. Some people with sacralization have lower back pain. It’s not clear whether sacralization causes the back pain. Study results have been mixed.

The association between sacralization and lower back pain was first described in 1917 by the Italian physician Mario Bertolotti, and was called “Bertolotti’s Syndrome.” The question of pain causality has been a subject of debate in the medical literature ever since.

A 2013 review of medical studies of lower back pain found that the number of people with lower back pain who also had sacralization ranged from 6 to 37 percent. A 2015 study suggested that people with lower back pain who have sacralization may have more severe pain.

Other symptoms associated with sacralization may include:

  • arthritis at the fusion site
  • bursitis
  • disc degeneration
  • biomechanical difficulties in movement
  • limits to range of motion
  • posture control problems
  • scoliosis
  • leg pain, buttock pain

Sacralization has several forms, classified according to whether the fusion seen on an X-ray is partial or total, and whether the fusion is on only one side (unilateral) or both (bilateral). The commonly used Castellvi classification is:

  • Type 1: a fusion at least 19 mm in width on one (1a) or both sides (1b)
  • Type 2: incomplete fusion with a pseudo joint created on one side (2a) or both sides (2b)
  • Type 3: complete fusion of the L5 to the sacrum on one side (3a) or the other (3b)
  • Type 4: combination of Type 2 and Type 3

The cause of sacralization isn’t yet known. It occurs during embryonic development, when the vertebrae begin to ossify, in about the eighth week.

There may be a genetic predisposition involved.

Estimates of the incidence of sacralization in the general population vary widely, from 4 to 36 percent. The wide range of estimates is attributed to differences of diagnostic methods and definition.

Among people under 30, an estimated 18.5 percent have sacralization.

A 2017 review suggests that the incidence of sacralization may vary with race. This review cites studies showing an incidence ranging from a low of 4 percent in China to 35.9 percent in Turkey.

To diagnose this condition, your doctor will first examine you and ask about your medical history and any pain you may have.

A sacralization diagnosis also requires X-rays of the lumbar spine. You may have flexion-extension X-rays, so that the doctor can view the lumbar region in different positions.

Your doctor may also order MRI imaging. To confirm a diagnosis, your doctor may use diagnostic injections of anesthetics or steroids in the area.

Treatment depends on the type and degree of sacralization and what your symptoms are. Each individual is different, and there’s no set treatment. The conservative treatment given for pain associated with sacralization is the same as for other lower back pain.

Pain relief

This may include the standard treatments for lower back pain:

  • anti-inflammatory drugs
  • muscle relaxants
  • steroid injections

If you don’t get relief from steroid injections, this may be an indication that you need surgery.

Physical therapy

Physical therapy can help to strengthen and stabilize the muscles involved and improve movement.

A 2015 study reports that the Alexander technique of muscle retraining helps with posture and neuromuscular coordination. The same study notes that the Pilates method may be more effective than other physical therapy or exercise in strengthening the pelvic-lumbar region.

Chiropractic techniques are also reported to provide relief, by spinal manipulation, soft tissue work, stretching, and exercise.

Other treatments

There are a few studies of other promising treatments.

A local anesthetic combined with radiofrequency strips in the pain area is reported to have provided pain relief in one case. The authors recommend further research in this technique.

A 2015 study reported on the use of electric denervation as a minimally invasive method for pain relief in the space between the 5th lumbar vertebra and the sacrum.


Only 43 cases of surgery for sacralization problems have been reported in the medical literature. More studies are needed to better understand when surgery may be helpful.

Surgery may be recommended to correct specific disc or other abnormalities that result from the sacralization. For example, sacralization may cause strain on the disc between the fourth and fifth vertebrae, leading to disc slippage or degeneration. It can also cause compression of the spinal nerve and pain in your spine or legs, scoliosis, or sciatica.

Sacralization is a common congenital abnormality that often has no symptoms. Whether or not it causes back pain has been a subject of debate since sacralization was first described. If you have pain symptoms, conservative and surgical treatments are available.