General
- LSTV is an anomalous vertebra with intermediate morphologic characteristics between the sacral and the lumbar vertebrae
- its transverse processes are enlarged and can articulate with the sacrum or the ilium
- LSTV with articulation of some degree—whether partial (pseudoarthrosis) or complete fusion—is defined as either sacralization of the lowest lumbar segment or lumbarization of the most superior sacral segment of the spine
- Might be associated with back pain
- Can impinge on L5 nerve root and cause leg pain
- Surgery can be complex as the Tranverse process can be quite deep
Numbers
Study/Population | Sample Size | Prevalence (%) | Notes |
General population review | - | 4%–30% | Variation by imaging/population |
Indian LBP patients | 450 | 28% | Castellvi Classification |
S. African adults | 1,032 | 9.3% | Morphological analysis |
NE Indian hospital | 350 | 19.7% | Castellvi: Ib > IIIb > IIB |
Large surgical series | 4,816 | 8.1% | Castellvi types IIA & IIIA most common |
Young adults (US/Canada) | 153 | 8.5%–12.4% | Mainly type II per Castellvi |
Castellvi classification of LSTV
Type | Subtype | Description | Morphological Features | Clinical associations |
Type I | Ia– unilateral Ib– bilateral | Dysplastic transverse process measuring ≥19 mm without articulation | Slight widening of L5 transverse process; no joint or fusion | No difference in the incidence or location of disc herniations compared to normal anatomy. |
Type II | IIa– unilateral IIb– bilateral | Pseudo-articulation (diarthrodial joint) between enlarged transverse process and sacrum | Partial fusion or joint formation (incomplete sacralization) | • Disc herniation occurs at the level of the transitional vertebra. • Increased incidence of disc herniation at the level immediately above the LSTV (proximal segment). |
Type III | IIIa– unilateral IIIb– bilateral | Complete osseous fusion between transverse process and sacrum | Full bony union; often loss of mobility at L5–S1 | • No disc herniations detected at the level of the LSTV. • No increase in herniation incidence just above the LSTV level. |
Type IV | — | Mixed: Type II on one side, Type III on the opposite side | Asymmetrical fusion producing pelvic tilt or back pain | • No disc herniations detected at the level of the LSTV. • No increase in herniation incidence just above the LSTV level. |
Clinically significance:
- Symptom Correlation and Back Pain Risk
- Types II and IV (the pseudoarticulation part), are strongly associated with increased risk of low back and buttock pain
- Pseudoarticulation part: has an enlarged transverse process creates a joint-like connection with the sacrum → This “false joint” behaves like an abnormal articulation → joint is prone to degenerative changes such as arthritic transformation and osteophyte (bone spur) formation → to local mechanical pain and inflammation
- LSTV alters the normal biomechanics of the lumbar spine.
- Types II and III (pseudoarticulation or complete fusion) can lead to early degenerative changes or disc herniation at the segment above the transitional vertebra because abnormal mobility or stress is shifted cranially
- Pain and degeneration are less commonly associated with Castellvi type I ("forme fruste") than with higher grades, but recognition is still important for anatomical mapping.
- Surgical Planning and Level Identification
- LSTVs pose a risk for wrong-level surgery because transitional anatomy can mislead vertebral counts on imaging.
- Castellvi classification helps reliably identify and map vertebrae, reducing surgical error risk.
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