What percentage of the population has a sacralized L5 vertebra?

Prevalence of Sacralized L5 Vertebra

Approximately 4.8% to 15% of the population has a sacralized L5 vertebra, with complete bilateral sacralization occurring in roughly 4.8% and any form of lumbosacral transitional vertebra (LSTV) present in 12.9% to 14.9% of individuals.

Population Prevalence Data

The frequency of L5 sacralization varies based on the degree of fusion assessed:

• Complete bilateral sacralization occurs in 4.8% of the population, where the L5 vertebra is fully fused with the first sacral segment 1
• Unilateral complete sacralization is present in 1.2% of individuals 1
• Any form of LSTV (including both sacralization and lumbarization) affects 12.9% to 14.9% of patients undergoing spinal surgery, with sacralization representing approximately half of these cases 2, 3

Clinical Significance and Detection

Surgical Implications

L5 sacralization creates substantial challenges in clinical practice that extend beyond its anatomical presence:

• Spinal level miscounting occurs in 54% of patients with LSTV at initial outpatient evaluation, with S1 lumbarization being miscounted more frequently (28 cases) than L5 sacralization (10 cases) 2
• Surgical plan alterations are required in 15% of cases after recognition of the true spinal anatomy through whole-spine radiography 2
• Fusion outcomes may be compromised in patients with type II or III L5 sacralization undergoing L4-L5 posterior lumbar interbody fusion, showing significantly lower fusion rates at 1 year compared to those without sacralization 4

Biomechanical Considerations

The presence of sacralized L5 fundamentally alters spinal mechanics:

• Sacralization represents a structural compensation for smaller sacral dimensions, with the fusion increasing sacral height, width, and auricular surface area 1
• The stress concentration at L4-L5 level in patients with sacralized L5 was historically thought to promote degenerative spondylolisthesis, though radiological studies show this influence may be less significant than previously expected 5
• Pelvic incidence measurements differ substantially when measured from L5 versus S1 in sacralized anatomy (24.5° vs 55.7°), with S1 measurements correlating better with health-related quality of life outcomes 3

Diagnostic Pitfalls and Prevention

Essential Imaging Protocol

To avoid surgical errors related to LSTV:

• Whole-spine radiography should be obtained before any lumbar surgical intervention to establish accurate vertebral counting 2
• MRI evaluation of the entire spine is crucial when surgical intervention is considered, as more than 20% of patients with spinal anomalies have associated neural axis abnormalities 6
• Surgeons should measure pelvic parameters from S1 rather than L5 in patients with sacralized anatomy, as L5 measurements underestimate spinal deformity and correlate less with functional outcomes 3

Recognition Strategies

The most reliable approach to identifying sacralization involves:

• Systematic vertebral counting from C1 downward on whole-spine imaging rather than assuming five lumbar vertebrae 2
• Recognition that innocent coccygeal dimples (present in 4% of the population) are distinct from pathologic lumbosacral dermal sinus tracts and should not be confused with spinal anomalies 7
• Understanding that sacralization may be asymptomatic but requires documentation to prevent level-selection errors during interventional procedures 2