Spondylolisthesis

Spondylolisthesis is the movement of one vertebrae in either the anterior or posterior direction due to instability.

The vertebrae can be divided in to 3 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.

• Spondylolisthesis is commonly associated with spondylolysis (see 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 in to spondylolisthesis is about 4 - 5%.¹

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 e.g. minimal trauma or even standing.⁴ Once this fibrous tissue weakens the vertebrae 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 to develop spondylolysis than football players.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.

1. Stable or unstable
2. Asymptomatic or symptomatic.

• 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

Need to rule out other causes of back pain e.g. spinal cord lesion, multiple myeloma, vertebral fracture.

• Bloods - 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 pre-operatively to provide information regarding nerve compression and soft tissue.

Conservative treatment

• Bed rest
• Avoid activities if > 25% slippage¹
• Analgesia e.g. paracetamol, NSAID's, codeine phosphate
• Bracing⁶
• Physiotherapy.

These measures only provide temporary relief.

Curative treatment

• Curative therapy involves reconstructive surgery in which the affected vertebrae is fused with another normally aligned vertebrae (both anteriorly and posteriorly). The intervertebral disc is usually also removed as it is inevitably damaged. Fusion techniques ca 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 vertebra 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 needs to be a risk-benefit assessment but may be necessary if conservative measures fail.
• All high grade slips i.e. 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.

Spondylolisthesis is a benign condition which runs a chronic course.