Anatomy of the vertebrae

The vertebrae can be divided into three portions:

• Centrum - involved in weight bearing.
• Dorsal arch - surrounds and protects the spinal cord.
• Posterior aspect - protrudes and can be palpated on the lower back.

These three areas are present in the fetus and become ossification centres. The vertebrae also have spinous processes and articular processes.

Terminology

• Spondylosis - degeneration of the vertebrae which occurs commonly with ageing and is the result of deformity of the joint and associated with osteophyte formation.
• Spondylolysis - the dorsum of the vertebra fails to fuse with the centrum. Occurs in 3-6% of patients and results from a defect in the pars interarticularis. This most commonly affects lower lumbar vertebrae, eg L4 or L5.
• Spina bifida - the two dorsal arches fail to fuse.

Epidemiology

• Spondylolisthesis is commonly associated with spondylolysis (see box, below). The incidence of spondylolysis is 3-6% in the general population.^[1] The prevalence is higher in adolescents with Scheuermann's disease, athletes and gymnasts (up to 12%).^[2]
• One study revealed a 5.7% prevalence of spondylolysis and 3.1% prevalence of spondylolisthesis in 510 consecutive abdominal CT scans performed for other reasons.^[3]
• 70% of patients with isthmic spondylolysis will develop spondylolisthesis.^[1] However, prevalence rates of spondylolisthesis of up to 30-50% have been reported in Eskimo populations. The risk of spondylolysis developing into spondylolisthesis is about 4-5%.^[1]

Aetiology

Spondylolysis is very common and often picked up coincidentally when imaging for other illnesses. Many patients will be asymptomatic. When spondylolysis develops, the fibrous tissue connecting the centrum to the dorsal arch becomes weakened. This weakness is enhanced under certain conditions, eg minimal trauma or even standing.^[4] Once this fibrous tissue weakens, the vertebra can slip forward or backward, resulting in true spondylolisthesis.

Factors involved

• Mechanical factors are important, as evidenced by increased rates in athletes and gymnasts. Also, cricketers are more likely than football players to develop spondylolysis.^[5]
• There is a congenital predisposition, although the exact nature of the genetics is not understood
• Damage to the pars interarticularis is thought to be the initial event.

Types of spondylolisthesis

• Stable or unstable
• Asymptomatic or symptomatic

Presentation

• Back pain - worse with activity and may be associated with nerve root compression leading to sciatica and radiation of the pain.
• Sensory abnormalities resulting from nerve compression.
• Gluteal muscle atrophy from disuse.
• Change in bowel and bladder function and paralysis of the lower limbs - due to cauda equina syndrome.
• Adolescents often have abnormal posture (enhanced lordosis) and a waddle gait.
• The waddle gait is due to tightened hamstrings which means the pelvis has to be rotated in order to walk.

Presenting features according to age

Differential diagnosis

Other causes of back pain need to be ruled out - for example, spinal cord lesion, multiple myeloma, vertebral fracture.

Investigations^[1]

• Blood tests - looking for infection, myeloma, hypercalcaemia/hypocalcaemia.
• Lateral spinal X-rays - will show spondylolisthesis.
• Oblique spinal X-rays - will detect spondylolysis.
• CT scan of the spine.
• MRI of the spine - commonly performed preoperatively to provide information regarding nerve compression and soft tissue.

Management

Conservative treatment

• Bed rest.
• Avoidance of activities if there is >25% slippage.^[1]
• Analgesia, eg paracetamol, non-steroidal anti-inflammatory drugs (NSAIDs), codeine phosphate.
• Bracing.^[6]
• Physiotherapy.

These measures only provide temporary relief.

Curative treatment

• Curative therapy involves reconstructive surgery in which the affected vertebra is fused with another normally aligned vertebra (both anteriorly and posteriorly). The intervertebral disc is usually also removed, as it is inevitably damaged. Fusion techniques can be associated with neurological complications.^[7] Fusion techniques are associated with less long-term disability, especially in adolescents.^[7] There are various fusion techniques that are used - however, a systematic review of the different types failed to find any major differences in terms of clinical and radiological outcomes.^[8]
• Other types of surgery can involve reduction therapies to reduce spondylolisthesis with carefully controlled force and limited distraction. This is achieved by applying forces to the affected vertebral bodies by applying screws.
• Surgery is commonly complicated by pseudoarthrosis (approximately 40% of cases) which may be disabling and result in chronic pain years down the line.^[1] Therefore, decisions regarding surgery in patients with low-level slippage need to be a risk-benefit assessment but may be necessary if conservative measures fail.
• All high-grade slips, ie 50% or greater, need surgical repair.^[1]
• Cauda equina syndrome needs to be promptly managed to avoid permanent paralysis and is a definite indication for surgical repair.

Complications of surgical repair^[9]

Prognosis

Spondylolisthesis is generally a benign condition; however, it runs a chronic course and is thus the cause of much morbidity and disability.