What Is Sacralization of L5?
Sacralization of L5 is a congenital spinal variant in which the fifth lumbar vertebra (L5) is partially or fully incorporated into the sacrum, creating four rather than five mobile lumbar segments. This occurs due to anomalous vertebral segmentation during embryonic development and is detected on X-ray or MRI as a transitional vertebra.
Classification: Castellvi System
| Type | Description | Symptom Risk |
|---|---|---|
| Type I | Enlarged transverse process (> 19 mm width) | Low |
| Type IIA | Unilateral pseudoarticulation | Moderate (Bertolotti Syndrome) |
| Type IIB | Bilateral pseudoarticulations | Moderate |
| Type IIIA | Unilateral complete fusion to sacrum | Low to Moderate |
| Type IIIB | Bilateral complete fusion | Low |
| Type IV | Unilateral complete fusion + contralateral pseudoarticulation | High |
Symptoms of Sacralization of L5
Many people with sacralization of L5 are entirely asymptomatic and discover the variant incidentally during imaging for another reason. When symptomatic, presentations include:
- Low back pain — particularly at the L4-L5 level (the newly stressed segment)
- Buttock pain — arising from the pseudoarticulation in Type II sacralization (Bertolotti Syndrome)
- Sciatica — if L4-L5 disc herniation occurs secondary to increased segmental stress
- Reduced lumbar flexion — from the restricted lumbosacral junction
- Asymmetric low back pain in unilateral (Type IIA or IIIA) cases
Why Sacralization Causes Problems
Fusing L5 to the sacrum removes one spinal motion segment. This transfers all the flexion-extension load that would have been distributed across five segments to only four. The L4-L5 disc becomes the new lumbosacral junction and bears significantly increased stress, predisposing it to:
- Accelerated disc degeneration
- Earlier onset disc herniation
- Facet joint osteoarthritis at L4-5
- Spinal stenosis at L4-5
Physiotherapy for Sacralization of L5
Treatment Goals
- Reduce load at the L4-L5 segment through muscle stabilisation
- Improve thoracolumbar mobility to compensate for reduced lumbosacral motion
- Strengthen hip extensors and abductors to offload lumbar structures
- Manage any associated disc pathology or nerve root irritation
Key Exercises
Core Activation:
- Transversus abdominis (belly-draw-in) activation — foundational for lumbar segment protection
- Dead bug exercise — deep core challenge without lumbar loading
Hip Strengthening:
- Bridge exercise — gluteus maximus and hamstring activation
- Clamshell — gluteus medius for lateral pelvic stability
Mobility Work:
- Thoracic rotation — improves thoracolumbar compensatory motion
- Hip flexor stretching — prevents anterior pelvic tilt increasing L4-5 stress
- Cat-camel — segmental lumbar mobility within available range
Postural Correction:
- Ergonomic sitting modifications
- Standing posture training with neutral pelvis
Manual Therapy
A physiotherapist may apply joint mobilisation at the L3-L4 or L4-L5 levels to maintain available motion. Neural mobilisation may be used if sciatic nerve irritation is present from L4-5 disc pathology.
When Is Intervention Required?
- Conservative physiotherapy is first-line for all symptomatic sacralization cases
- Corticosteroid injection into the pseudoarticulation may help Bertolotti Syndrome pain not responding to physiotherapy
- Surgery (resection of the abnormal transverse process or fusion) is rarely indicated and only after extensive conservative care failure
For related conditions, see L4-L5 disc prolapse treatment and lumbar spondylosis exercises.
References
- Castellvi AE et al. Transitional lumbosacral vertebrae and their relationship with lumbar extradural defects. Spine. 1984.
- Elgafy H et al. Bertolotti's syndrome: a clinical and radiological study. European Spine Journal. 2009.
- Nardo L et al. Lumbosacral transitional vertebrae: association with low back pain. Radiology. 2012.