Understanding Bertolotti’s Classification: A Guide to Lumbosacral Transitional Vertebrae (LSTV)

Back pain is one of the most common complaints in both clinical and outpatient settings. While many cases are attributed to muscular strain, disc degeneration, or postural issues, there's a lesser-known anatomical variant that may underlie chronic lower back discomfort in a subset of patients—Bertolotti’s Syndrome. At the heart of this condition lies the lumbosacral transitional vertebra (LSTV), a congenital anomaly that can cause altered biomechanics of the spine.

To better understand and classify these anomalies, Castellvi et al. developed what is now widely known as Bertolotti’s Classification. This system is crucial for diagnosing, managing, and communicating about LSTVs.

Let’s break it down.

What Is a Lumbosacral Transitional Vertebra?

An LSTV is a congenital condition where the last lumbar vertebra (usually L5) shows characteristics of the sacrum, or the first sacral vertebra (S1) has features of a lumbar vertebra. This blending is known as sacralization (L5 resembling sacrum) or lumbarization (S1 resembling lumbar vertebra).

While many people with LSTVs remain asymptomatic, in some, the altered biomechanics lead to Bertolotti’s Syndrome—a source of persistent low back pain, especially in young adults.

Bertolotti’s (Castellvi’s) Classification System

The classification, proposed by Castellvi et al. in 1984, divides LSTVs into four main types (I–IV) based on radiographic features—especially the articulation or fusion between the L5 transverse process and the sacrum or ilium.

Type I – Dysplastic Transverse Process

• Ia: Enlarged transverse process (>19 mm) unilaterally
• Ib: Enlarged transverse process bilaterally
• No articulation or fusion with the sacrum
• Often asymptomatic

Type II – Incomplete Lumbarization or Sacralization (Pseudoarticulation)

• IIa: Unilateral pseudoarticulation of transverse process with sacrum
• IIb: Bilateral pseudoarticulation
• May lead to pain due to movement at the pseudo-joint
• Most common type associated with Bertolotti’s Syndrome

Type III – Complete Fusion

• IIIa: Unilateral complete fusion of the transverse process to sacrum
• IIIb: Bilateral complete fusion
• Less movement; may limit mobility or cause adjacent segment degeneration

Type IV – Mixed Type

• One side shows pseudoarticulation (Type II), and the other side shows complete fusion (Type III)
• This asymmetry may lead to biomechanical imbalances and pain

Diagnosis

LSTVs are best visualized on plain X-rays (AP/lateral views), especially lumbosacral spot views. Advanced imaging like CT or MRI can help assess:

• Disc pathology
• Nerve root involvement
• Inflammatory changes in pseudoarticulations

A high iliac crest or abnormally positioned transverse processes on imaging often hint at the presence of an LSTV.

Clinical Relevance

• Differential Diagnosis: Important in young patients with chronic low back pain without typical disc disease
• Management Options: Conservative treatment (PT, NSAIDs), guided injections, or in rare cases, surgical resection of the pseudoarticulation
• Biomechanics: Altered motion at lumbosacral junction can accelerate degeneration in adjacent discs or joints

Key Takeaways

• Bertolotti’s classification provides a structured way to identify and describe LSTVs
• Type II (pseudoarticulation) is most commonly associated with Bertolotti’s Syndrome
• Radiographic assessment is key to diagnosis
• Treatment should be individualized based on symptoms, not just imaging

Final Thoughts

While often overlooked, lumbosacral transitional vertebrae can be a significant contributor to chronic low back pain, especially in younger individuals. Knowing how to classify and identify these anomalies using Bertolotti’s Classification allows for better diagnosis, communication, and ultimately, management of these patients.