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Lumbosacral Transitional Vertebra

At the bottom of your lumbar spine is the L5 vertebra, the fifth bone in the low back. In the typical spine, the L5 is the last part of the spine that can bend. In medical terms, the L5 is the lowest mobile segment 

But due to abnormal bone growth—an occurrence that ranges from 4 to 30% of the time—the L5 can lose its ability to move. During fetal development, the transverse processes at the side of L5 broaden and grow outward toward the sacrum.   

This congenital variation is known as a sacralized lumbar vertebra. A more general term you might see on your MRI report is a transitional lumbar vertebra or a lumbosacral transitional vertebra. There are different types of sacralized lumbar vertebra which is determined by:  

  • whether the L5 has an abnormal transverse process on one or two sides 
  • extent of fusion (connection) with the sacrum 
    • No fusion — the enlarged transverse processes grow toward but to not connect at any point with the sacrum  
    • Partial fusion — one or two transverse processes partially fuse with the sacrum  
    • Complete fusion — one or two transverse processes completely fuse with the sacrum  

Does a sacralized lumbar vertebra cause pain?   

Sometimes  

There is disagreement within the medical field about whether lumbar transitional vertebrae can cause pain. My observation is it often does not cause pain.   

Keep in mind that, as a congenital (birth) defect, a sacralized lumbar vertebra is present from the beginning of life. Being generally pain-free, these individuals will not even know they have a sacralized L5 unless they develop an injury.   

When the LSVT is visualized on spinal imaging, I observe the following errors:  

  • The LSVT is entirely overlooked and not mentioned in the radiology report  
  • The extent of fusion to the sacrum is not described in the radiology report 
  • The LSVT is assumed to be “incidental” and not related to the symptoms. 

What spine imaging is best for seeing a LSVT?  

A LSVT can be seen on an MRI. The best imaging, however, is: 

  • A CT scan  
  • A Ferguson x-ray  
    • AP radiographs — this means a front view 
    • Angled (tilted) upward at 30° 

The CT scan provides the best quality images. The Ferguson x-ray serves as a more accessible initial screen when a CT is not immediately available or you want to avoid the additional radiation involved in a CT scan.  

Where does an LSVT cause pain?  

The LSVT can cause pain at the:  

  • Region of enlarged transverse process 
  • Connection site between the transverse process and the sacrum  
  • Facet joint  
  • Nerve roots compressed by the enlarged transverse processes  
  • Disc level above the LSVT (at L4-L5)  

How does the LSVT change the biomechanics of the spine?   

At L5-S1 — The level of the LSVT  

Let’s start with the disc at the level of the LSVT. There will be reduced movement here when there is partial or complete fusion at either side of sacralized L5.   

A partially fused LSVT will reduce the movement at L5-S1.   

A fully fused LSVT will virtually eliminate all movement at L5-S1.   

Restricted movement at the lowest level of the lumbar spine protects the joint from damage and degeneration from bending, twisting, and other forces. It’s like the protection your elbow has in a cast—hard to overload a joint that you can’t move.   

At L4-L5 — The level above the LSVT  

But the disc above the level of the LSVT is at risk for excessive movement (hypermobility). The incidence of L4-L5 disc injury is actually similar between people with and people without LSVT.   

What differs is the LSVT-group L4-L5 disc injury has worse pain and more nerve symptoms. The LSVT group is more likely to experience significant:  

  • Discogenic pain  
  • Nerve symptoms  
  • Facet injury  
  • Thinning of the spinal ligaments (the iliolumbar ligaments) 
  • Isthmic spondylolisthesis 

How does a LSVT cause pain?   

The altered biomechanics of an LSVT can cause pain in the following sites.   

Anatomy  

Location of Pain
  

Reason for pain 

False Joint 

At and close to the SI joint on the side(s) of the false joint 

The false joint (anomalous articulation) is the partial connection between the L5 transverse process and forms a connection that looks like a joint. The movement at the false joint can cause a type of bone pain—at the transverse process or the sacrum—from the grinding between them.  

 

*Note there is no false joint if there is a complete fusion of the transverse process with the sacrum.  

L4-L5  In the middle of the back about an inch up from L5-S1  L4-L5 disc pain is more prevalent when there is a complete fusion of one or two transverse processes at the LSVT. In a complete fusion, the elimination of bending at the L5-S1 level means that bending forces are excessively transmitted to the level above the fusion. Disc bulges and sciatica become more probable and severe than in patients who do not have a LSVT.  
Facet Joint Pain  To the sides of the low back, usually within two inches of the middle of the back  Facet pain occurs most often in the side away from the fusion, in cases when there is a fusion to only one side. The one-sided LSVT fusion limits bending and twisting to one side of the body, leading the opposite side facet joint to become hypermobile.  
Nerve root pain at L5-S1  Sciatica to one or both legs   The enlarged transverse processes in an LSVT can pinch the nerve roots against the broad wing of the sacrum.  

Pain from any of these mechanisms arising from an LSVT is also known as Bertolotti’s syndrome. I avoid this term because I find it inaccessible to clinicians and back-pain sufferers alike.  

No offense Is intended toward the impressive Italian physician Mario Bertolotti who first described LSVT-related pain in 1917.   

Why Should I Care About a LSVT?   

There are two main reasons you should care about a LSVT:  

  1. An LSVT can cause pain, as detailed above. 
  2. An LSVT can confuse your surgeon resulting in an operation at the wrong level. Most wrong-level spine surgery-occurs in patients with variant spinal anatomy such as LSVTs 

What are common pain triggers for LSVT?   

The LSVT pain are frequently triggered by the following types of forces:  

  • Bending and twisting  
  • Pelvic stresses 
  • Lunges 
  • Cycling  
  • Sprinting  
  • Single-leg exercises 
  • Single-leg squats 
  • Singe-leg deadlifts 
  • Balancing on one leg 

Avoidance of the offending trigger is required to wind down your pain and allow tissue healing.  

What procedures can be done?  

Injections with steroid and local anesthetics to:  

  • A false joint  
  • An irritated facet joint 
  • Affected nerve roots 

Though rarely done, there are scientific reports of successful treatment involving the removal (resection) of the overgrown transverse process.   

Select References  

Konin, G. P., and D. M. Walz. “Lumbosacral transitional vertebrae: classification, imaging findings, and clinical relevance.” American Journal of Neuroradiology 31.10 (2010): 1778-1786. 

Jancuska, Jeffrey M., Jeffrey M. Spivak, and John A. Bendo. “A review of symptomatic lumbosacral transitional vertebrae: Bertolotti’s syndrome.” International journal of spine surgery 9 (2015).  

Hughes, R. J., and A. Saifuddin. “Imaging of lumbosacral transitional vertebrae.” Clinical radiology 59.11 (2004): 984-991.  

Nardo, Lorenzo, et al. “Lumbosacral transitional vertebrae: association with low back pain.” Radiology 265.2 (2012): 497-503.  

Luoma, Katariina, et al. “Lumbosacral transitional vertebra: relation to disc degeneration and low back pain.” Spine 29.2 (2004): 200-205.