Spondylolisthesis is the movement of one vertebra relative to the others in either the anterior or posterior direction due to instability.
Anatomy of the vertebrae
The vertebrae can be divided into three portions:
- Centrum - involved in weight bearing. This is the body of the vertebra and is formed of cancellous bone.
- Dorsal arch - surrounds and protects the spinal cord. It carries the upper and lower facet joints of each vertebra which articulate with the facet joints of the vertebra above and below, respectively. The part of the vertebral arch between them is the thinnest part and is called the pars interarticularis, or the isthmus.
- Posterior aspect - protrudes and can be palpated on the lower back.
Images by Anatomography, via Wikimedia Commons. Click here to see a lumbar vertebra 1 close-up superior surface animation.
Spondylolysis and spondylolisthesis are separate conditions, although spondylolysis often precedes spondylolisthesis.
- Spondylolysis is a bony defect (commonly due to a stress fracture but it may be a congenital defect) in the pars interarticularis of the vertebral arch, separating the dorsum of the vertebra from the centrum. It may occur unilaterally or bilaterally. It most commonly affects the fifth lumbar vertebra and may cause back pain.
- Spondylolisthesis refers to the anterior slippage of one vertebra over another (or the fifth vertebra over the sacrum). There are five forms:
- Isthmic: the most common form, usually acquired in adolescence as a consequence of spondylolysis but often unnoticed until adulthood.
- Degenerative: developing in older adults as a result of facet joint osteoarthritis and bone remodelling.
- Traumatic (rare): resulting from fractures of the neural arch.
- Pathologic: from metastases or metabolic bone disease.
- Dysplastic: (rare): congenital, resulting from malformation of the pars.
- Spondylosis is a general term for degenerative osteoarthritic changes in the spine. It involves dehydration of the intervertebral discs with consequent narrowing of the intervertebral spaces. There may be changes in the facet joints with osteophyte formation and this may put pressure on the nerve roots, causing motor and sensory disturbance.
- Spondylolysis is particularly a condition of young people, usually occurring between the ages of 6 and 16. It is the most common cause of isthmic spondylolisthesis.
- Spondylolysis affects 3-6% of the population but up to 12% of young athletes like gymnasts, presumably due to impact-related stress fractures:
- There may be pre-existing weakness and this may be hereditary.
- Over 90% of cases are low-grade. At-risk activities include gymnastics, diving, tennis, cricket, weightlifting, football and rugby. Boys are more commonly affected than girls.
- Isthmic spondylolisthesis affects around 5% of the population but is more common in young athletes. 60-80% of people with spondylolysis have associated spondylolisthesis.[1, 2]
- 90% of cases of spondylolysis and spondylolisthesis affect L5 and most of the remainder affect L4.
- Degenerative spondylolisthesis is more common in older people, particularly women.
- Traumatic, metastatic and dysplastic spondylolistheses are relatively rare.
- Studies have suggested that the overall prevalence of spondylolisthesis is around 12% in the adult population. Many cases are asymptomatic.
Spondylolisthesis commonly occurs due to a fracture or defect in the pars interarticularis, the narrowest part of the posterior vertebral arch between the upper and lower facet joints. When this is breached, the upper facet joint may no longer be able to hold the vertebra in place against the downward force of body weight and forward/downward slippage occurs.
Risk factors that increase the risk of spondylolysis developing into spondylolisthesis include:
- Female gender.
- Young age.
- Presence of spina bifida or spina bifida occulta.
- Vertebral wedging.
- Positive family history.
- Certain high-impact sports, as evidenced by increased rates in athletes and gymnasts.
Types of spondylolisthesis
- Stable or unstable.
- Asymptomatic or symptomatic.
- Graded according to degree of slippage; the Meyerding classification is based on the ratio of the overhanging part of the superior vertical body to the anterio-posterior length of the inferior vertebral body:
- Grade I: 0-25%.
- Grade II: 26-50%.
- Grade III: 51-75%.
- Grade IV: 76-100%.
- Grade V (spondyloptosis): >100%.
- Graded according to type; the Wiltse classification (1976):
- Type I: dysplastic (congenital).
- Type II: isthmic: secondary to a lesion involving the pars interarticularis:
- Subtype A: secondary to stress fracture.
- Subtype B: result of multiple healed stress fractures resulting in an elongated pars.
- Subtype C: acute pars fracture (rare).
- Type III: degenerative.
- Type IV: post-traumatic: fracture in a region other than the pars.
- Type V: pathological: diffuse or local disease.
- Type VI: iatrogenic.
- Most cases of spondylolysis are asymptomatic and identified incidentally.
- It may present with low back pain provoked by lumbar extension, paraspinal spasm and tight hamstrings.
- It frequently does not show on X-ray. It is important to consider it in the differential diagnosis of back pain, as its identification can prevent progression and avoid the potential need for aggressive intervention.
The presentation of spondylolisthesis varies slightly by type although common symptoms include exercise-related back pain, radiating to the lower thighs, which tends to be eased by rest, particularly in positions of spinal flexion.
- Most patients are asymptomatic, even with progressing slippage.
- Symptoms often begin around the adolescent growth spurt.
- Back pain - worse with activity (particularly back extension) - this may come on acutely or insidiously..
- Pain may flare with sudden or trivial activities and is relieved by resting.
- Pain is worse with higher grades of disease.
- Pain may radiate to buttocks or thighs
- There are usually no neurological features with lower grades of slippage but radicular pain becomes common with larger slips. Pain below the knee due to nerve root compression or disc herniation would suggest more severe slippage. High degrees of spondylolisthesis may present with neurogenic claudication or even cauda equina impingement.
- Tightened hamstrings are very common
- There may be enhanced lordosis and a waddling gait with shortened step length.
- There may be gluteal muscular wasting.
- Pain is aching in nature and insidious in onset.
- Pain is in the low back and posterior thighs.
- Neurogenic claudication may be present with lower-extremity symptoms worsening with exercise.
- Symptoms are often chronic and progressive, sometimes with periods of remission.
- If lumbar stenosis is also present, reflexes may be diminished.
- Presentation and physical findings are similar to isthmic spondylolisthesis but with a greater likelihood of neurological compromise.
- Patients will have experienced acute trauma and are likely to have significant pain.
- Severe slips may cause cauda equina compression with bladder and bowel dysfunction, radicular symptoms or neurogenic claudication.
- Physical findings are as for the other types.
- Symptoms may be insidious in onset and associated with radicular pain.
- Physical findings are as for the other types.
Other causes of back pain need to be ruled out - eg:
- Ankylosing spondylitis.
- Mechanical lower back pain.
- Spinal cord lesion.
- Multiple myeloma.
- Vertebral compression fracture.
- Lumbar disc prolapse.
- Discitis/other spinal disc problems.
- Blood tests - looking for infection, myeloma, hypercalcaemia/hypocalcaemia.
- Lateral spinal X-rays - will show spondylolisthesis. These are best performed in the position of maximal pain.
- Oblique spinal X-rays - may (but will often not) detect spondylolysis.
- Radionuclide scintigraphy and CT may help in cases of spondylolysis in distinguishing progressing lesions of the pars from stable lesions.
- MRI is often performed perioperatively to look at relationships between the bony and neurological structures in the compromised area.
The goal of treatment is to relieve pain, stabilise the spinal segment and stop or reverse the slippage. Patients need to be evaluated for the presence of instability, as if there is an unstable segment early surgery will be needed.
If slippage is not more than 50% and there is no significant neurological compromise, treatment usually begins with non-operative measures but, if these fail, surgical intervention is generally indicated for pain relief and improvement of neurological symptoms.
- Complete bed rest for 2-3 days can be helpful in relieving pain, particularly in spondylolysis, although longer periods are likely to be counterproductive. Patients should try to sleep on their side as much as possible, with a pillow between the knees.
- Activity modification to prevent further injury. This may mean avoidance of activities if there is >25% slippage.
- Analgesia - eg, paracetamol, non-steroidal anti-inflammatory drugs (NSAIDs), codeine phosphate.
- Steroid and local anaesthetic injections are sometimes used around compressed nerve roots or even into the fracture area of the pars for diagnostic purposes.
- Bracing: a brace or corset may be recommended for a pars interarticularis fracture which is likely to heal. Researchers cite evidence of benefit for bracing with exercise in mild or even in more severe degrees of slippage. However, a 2009 meta-analysis concluded that bracing was not likely to fulfil this function and did not confer added benefit.[10, 11]
- Physiotherapy: this includes massage, ultrasound, bracing, mobilisation, biomechanical correction, hydrotherapy, exercises for flexibility, strength and core stability and a gradual return to activity programme
- More than 80% of children treated non-surgically will have full resolution of symptoms.
- A meta-analysis of observation studies suggested that around 80% of all patients treated non-operatively would have a successful clinical outcome after one year. Lesions diagnosed at the acute stage and unilateral lesions were the best subgroups.
- If there is evidence of progression or if conservative measures are ineffective then surgical therapy may be offered. This depends also on degree and aetiology.
- Surgical intervention involves a prolonged rehabilitation period so it is generally not considered until conservative treatments have failed. An exception would be in the case of significant instability or neurological compromise and in high-grade slips.
- Surgical therapy involves fusing the affected vertebra with a neighbouring normally aligned vertebra (both anteriorly and posteriorly). The intervertebral disc is usually also removed, as it is inevitably damaged. The slipped vertebra may be realigned.
- Whilst most surgeons agree that decompression of the nerves is of benefit to patients, the benefit of realigning slipped vertebrae is uncertain. For example, when the spondylolisthesis is very gradual in onset, or in cases of congenital spondylolisthesis compensatory changes in the spine and musculature occur so that realignment may increase the possibility of further injury.
- There is good evidence that surgical treatment of symptomatic spondylolisthesis is significantly superior to non-surgical management in the presence of:
- Significant neurological deficit.
- Failed response to conservative therapy.
- Instability with neurological symptoms.
- Degree of subluxation of III or more.
- Unremitting pain affecting quality of life.
- A large systematic review concluded that reduction of displacement carried benefits over fusion alone, although a large retrospective review showed high complication rates, particularly for older patients with more severe disease.[14, 15, 16, 17]
- Fusion techniques can be associated with neurological complications in older patients with degerative spondylolisthesis, but in adolescent patients outcomes are good.[18, 15]
- Surgery is commonly complicated by pseudoarthrosis (non-union) which may result in chronic pain years down the line.
- In the case of spondylolysis, if surgery is offered it would involve pinning the defect. However, most cases are managed conservatively.
Complications of surgical repair
- Implant failure.
- Poor alignment of the fusion.
- Foot drop.
- Spinal cord compression.
- Chronic nerve injury/inflammation: neuropathic pain can persist in the face of apparent surgical success, possibly due to permanent changes in the nerves or a deregulation of pain control mechanisms.
Spondylolisthesis is generally a benign condition; however, it runs a chronic course and is therefore a cause of much morbidity and disability. In degenerative spondylolisthesis this will relate in part to the progress and prognosis of the underlying changes.
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