Spondylolysis and Spondylolisthesis
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Direct answer
Spondylolysis and spondylolisthesis differ in one key way: spondylolysis is a stress defect of the pars interarticularis, whereas spondylolisthesis is a forward slip of one vertebra on the one below, most often L5 on S1. The pars defect is seen best on oblique radiographs, where the defect appears as a collar across the Scotty dog's neck, and Meyerding grading measures the percentage of slip. Most cases are managed conservatively unless neurological deficit or progression develops.
What you must remember
- Pars interarticularis: the bony bridge between the superior and inferior facets, where repetitive extension stress in adolescents produces the defect of spondylolysis.
- Collar sign: on oblique lumbar films the pars is the neck of the Scotty dog, and a lucent defect across it appears as a collar, indicating spondylolysis.
- Meyerding grading: grade I is up to 25 percent forward slip, grade II 25 to 50 percent, grade III 50 to 75 percent, grade IV 75 to 100 percent, and grade V is complete slip, or spondyloptosis.
- Wiltse classification: type I is dysplastic, type II isthmic and the commonest, type III degenerative, type IV traumatic and type V pathological.
- Isthmic subtypes: the isthmic type is subdivided into lytic, elongated but intact, and acute fracture of the pars, which matters for prognosis and treatment.
- Clinical features: low back pain worsened by extension and sport, hamstring tightness and, in high-grade slips, a palpable step-off at the lumbosacral junction.
- Neural involvement: L5 root compression causes radicular pain and weakness, which is the main reason for surgery alongside progression.
Working up back pain in an adolescent athlete
A 14-year-old fast bowler has low back pain that worsens with extension and eases with rest, and a standing lateral radiograph shows a small forward slip. The pathway separates the pars defect from the slip and then matches the treatment to the grade and symptoms.
- Take the history and examine: pain on extension, hamstring tightness and a palpable step-off are recorded, with neurological examination of the legs.
- Obtain a standing lateral film: this measures the slip and assigns the Meyerding grade, and it shows the step at the lumbosacral junction.
- Obtain oblique films: the collar across the Scotty dog's neck confirms a pars defect, which is the bony lesion of spondylolysis.
- Use CT or MRI when needed: CT defines the pars defect and any healing, while MRI assesses the nerve root and any active stress reaction.
- Choose treatment by grade and symptoms: asymptomatic low-grade lesions are observed, and symptomatic cases receive activity modification and physiotherapy.
- Operate for red flags: neurological deficit, a progressive slip or pain that fails conservative care prompts surgery, usually fusion.
- Plan the fusion for high grade: significant slips are commonly managed with instrumented fusion, with reduction considered only in selected cases.
Where the exam tries to catch you
Spondylolysis questions usually test the difference between a defect and a slip, and the grading systems.
- Trap: labelling every pars defect as spondylolisthesis Correct: spondylolysis is a pars defect without slip, while spondylolisthesis requires the vertebra to shift forward.
- Trap: prescribing a brace for every symptomatic case Correct: most symptomatic cases respond to activity change and physiotherapy, and the evidence for bracing is limited.
- Trap: confusing the Meyerding grade with the Wiltse type Correct: Meyerding grades the amount of slip, while Wiltse classifies the cause, such as isthmic or degenerative.
Frequently asked questions
What is the Scotty dog collar sign in spondylolysis?
The Scotty dog collar sign is seen on oblique lumbar radiographs, where the pars interarticularis forms the dog's neck. A lucent collar across the neck indicates a pars defect, which is the bony lesion of spondylolysis.
How is spondylolisthesis graded by Meyerding?
Meyerding grading expresses the percentage of forward slip of one vertebral body on the one below. Grade I is up to 25 percent, grade II is 25 to 50 percent, grade III is 50 to 75 percent, grade IV is 75 to 100 percent, and grade V is complete slip.
What are the types in the Wiltse classification of spondylolisthesis?
The Wiltse classification divides spondylolisthesis into dysplastic, isthmic, degenerative, traumatic and pathological types. Isthmic spondylolisthesis, the commonest type, has subtypes for lytic, elongated and acutely fractured pars defects.
When does spondylolisthesis need surgery?
Surgery is considered for spondylolisthesis with neurological deficit, a progressive slip or pain that fails conservative treatment. Fusion with instrumentation is the usual choice for significant slips, while asymptomatic cases are followed up.