Bertolotti Syndrome (Lumbosacral Transitional Vertebra)

Bertolotti Syndrome refers to symptomatic low back pain caused by a lumbosacral transitional vertebra (LSTV). Named after Mario Bertolotti, an Italian radiologist who described the condition in 1917.

Definition:

A lumbosacral transitional vertebra is a congenital anomaly where the lowest lumbar vertebra (usually L5) has features of a sacral vertebra (sacralization), or the first sacral segment has features of a lumbar vertebra (lumbarization).

Epidemiology:

Key Concept:

Not all LSTVs cause symptoms. Bertolotti syndrome specifically refers to symptomatic LSTV. The challenge is determining whether the LSTV is the pain generator in a patient with low back pain.

Normal Lumbosacral Anatomy

L5 Vertebra:

• Largest vertebral body
• Short, broad transverse processes
• Wide intervertebral foramen
• Articulates with S1 via disc and facets

Sacral Ala:

• Lateral wing of S1
• Provides surface for SI joint
• Normal gap between L5 TP and sacral ala

LSTV Morphology

Type I - Dysplastic Transverse Process:

The transverse process is enlarged (≥19mm craniocaudal width) but does not articulate with the sacrum. This is considered a forme fruste of transitional vertebra.

Type II - Pseudoarticulation:

The enlarged transverse process forms a diarthrodial (synovial) joint with the sacral ala. This joint can develop degenerative changes similar to other synovial joints.

Type III - Complete Fusion:

The transverse process is completely fused to the sacral ala. No motion exists at this segment, concentrating stress at the level above.

Type IV - Mixed:

One side has pseudoarticulation (Type II), the other has complete fusion (Type III). This creates asymmetric biomechanics.

Biomechanical Implications

Motion Segment Changes:

When L5 is partially or completely incorporated into the sacrum, the L4-L5 disc becomes the functional lumbosacral junction. This disc experiences increased stress and is prone to early degeneration.

Contralateral Stress:

With unilateral LSTV (types a), the contralateral facet joint bears increased load due to asymmetric stiffness. This leads to contralateral facet arthropathy.

Embryology

Development:

LSTVs result from errors in vertebral segmentation during embryonic development. The HOX genes control segmentation of the axial skeleton. Mutations or variations in HOX gene expression can lead to transitional morphology.

Pain Mechanisms

Four Pain Generators:

Natural History

Many LSTVs are asymptomatic and discovered incidentally. Symptomatic patients typically present in their 20s-30s, earlier than typical degenerative low back pain. The condition may wax and wane, with some patients having prolonged symptom-free periods.

Castellvi Classification (1984)

The Castellvi classification, described in 1984, remains the standard system for classifying LSTVs based on the morphology of the transverse process and its relationship to the sacrum.

Clinical Correlation

Level Identification

Critical Importance:

LSTV can cause confusion in vertebral counting. A sacralized L5 may be counted as S1, leading to wrong-level surgery.

Methods to Identify Correct Level:

1. Whole-spine imaging - Count from C2 down
2. Identify T12 - Last rib-bearing vertebra
3. Iliac crest reference - Usually at L4 body
4. Rib counting on CT - Count from T1 down
5. Document clearly - Pre-operative planning essential

History

Pain Characteristics:

Important History Points:

• Duration and onset (often chronic, insidious)
• Previous imaging showing LSTV
• Failed treatments
• Radicular symptoms (suggests nerve involvement)
• Presence of leg symptoms (disc vs LSTV)

Physical Examination

Inspection:

• May have mild scoliosis (especially unilateral LSTV)
• Normal lumbar lordosis usually

Palpation:

• Tenderness over pseudoarticulation (lateral to midline)
• May be difficult to differentiate from SI joint tenderness
• Contralateral facet tenderness if overloaded

Range of Motion:

• Extension often painful
• Rotation to affected side may reproduce pain
• Flexion usually less painful

Neurological Examination:

• Usually normal
• If L5 radiculopathy: weak ankle dorsiflexion, altered sensation L5 dermatome
• Check for extraforaminal compression signs

Special Tests:

Red Flags

Rule out serious pathology. Bertolotti syndrome should be mechanical pain without red flags.

Imaging Protocol

X-ray (First Line):

The Ferguson view (AP with 30-35° cephalad tilt) provides the best visualization of the lumbosacral junction and LSTV.

CT Scan:

Best modality for bony detail of LSTV.

MRI:

Diagnostic Injection

Pseudoarthrosis Injection:

This is both diagnostic and therapeutic. Response to injection helps confirm LSTV as pain source.

Technique:

• CT or fluoroscopic guidance
• Needle into pseudoarticulation
• Inject local anesthetic and steroid

Interpretation:

• Greater than 50% relief = positive (LSTV is pain source)
• Partial relief = may have multiple pain generators
• No relief = consider other diagnosis

Other Injections:

• Facet injection (contralateral side) if facet suspected
• Selective nerve root block if radiculopathy

Laboratory Studies

Not typically required. If concern for inflammatory arthropathy, check:

• ESR, CRP
• HLA-B27 (spondyloarthropathy)

Algorithm

View larger

Treatment Algorithm

Conservative Management (First Line):

Duration: Trial of 6-12 weeks before interventional treatment.

Injection Therapy:

Indications:

• Failed conservative management
• Diagnostic confirmation
• Therapeutic trial

Options:

• Pseudoarthrosis injection (primary target in Type II)
• Contralateral facet injection (if facet pain suspected)
• Selective nerve root block (if radiculopathy)

Surgical Management

Indications:

• Failed conservative and injection therapy
• Confirmed LSTV as pain source (positive diagnostic injection)
• Significant functional impairment

Surgical Options:

Conservative/Injection Complications

Injection-Related:

• Infection (rare)
• Bleeding
• Nerve injury
• Steroid side effects

Surgical Complications

Resection:

• L5 nerve injury (proximity to pseudoarthrosis)
• Incomplete resection (recurrent pain)
• Instability (rare if technique appropriate)
• Wound complications

Fusion:

• Pseudarthrosis
• Hardware failure
• Adjacent segment disease
• Nerve injury
• Infection

Wrong-Level Surgery

This is a particular risk with LSTV due to difficulty in level counting.

Prevention:

• Whole-spine imaging pre-operatively
• Multiple methods to confirm level
• Intraoperative imaging confirmation
• Clear documentation of transitional anatomy

Bertolotti syndrome is a diagnosis of attribution: an LSTV is present in a substantial minority of the population, so the key task is distinguishing LSTV-driven pain from overlapping causes of mechanical low back and buttock pain. A positive diagnostic injection into the pseudoarticulation is the single most useful discriminator.

Global epidemiology:

Guideline landscape (side by side):

There is no condition-specific society guideline dedicated to Bertolotti syndrome. Management is governed by general low back pain and wrong-level-surgery guidance, which differs by region:

Registry note:

No arthroplasty/implant registry tracks Bertolotti procedures specifically, as resection is non-instrumented and fusion volumes are low. Wrong-level spinal surgery is, however, captured by national patient-safety/never-event reporting systems in several countries, where transitional anatomy is a recurrent contributing factor.

High- vs limited-resource practice variation:

• Well-resourced settings: CT and MRI are routine; CT- or fluoroscopy-guided diagnostic injections and image-navigated minimally invasive pseudoarthrectomy are available; multidisciplinary review for complex level identification.
• Limited-resource settings: Diagnosis often rests on plain radiographs (Ferguson view) and clinical correlation; diagnostic injection access may be limited; treatment is predominantly conservative, with surgery reserved for clearly refractory, well-localised cases.

Wrong-level surgery — universal principle:

Prevention of wrong-level surgery is a global surgical-safety priority. Multiple level confirmations (whole-spine imaging, intraoperative imaging with a marker, consistent documented nomenclature) are required wherever transitional anatomy is present, irrespective of health system.

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