01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Spondylolisthesis describes vertebral translation and does not by itself identify cause, symptoms or stability. The Wiltse framework distinguishes dysplastic, isthmic, degenerative, traumatic, pathological and iatrogenic mechanisms. Degenerative slip arises from disc and facet failure with the pars intact, classically at L4–5 in older adults and often alongside stenosis. Isthmic disease reflects a pars interarticularis lesion and commonly affects L5–S1. These categories have different age distributions, neural anatomy and operative questions.
Symptoms range from none to mechanical low-back pain, radicular pain or neurogenic claudication. Degenerative slip can narrow the central canal and lateral recess. Isthmic L5–S1 slip can narrow the foramen and affect an exiting L5 root as disc height is lost. Examination includes gait, posture, step deformity, hamstring tightness, root power, sensation and reflexes, plus hip and vascular assessment. A slip found during unrelated imaging should not be treated merely because it has a grade.
Meyerding grade expresses translation as a percentage of the lower vertebral body: grade I less than 25%, II 25–50%, III 50–75%, IV 75–100%, with spondyloptosis beyond complete translation. Grade helps describe anatomy but does not replace assessment of progression, slip angle, balance, neural compression or symptoms. Standing radiographs show loaded alignment; flexion–extension views can explore motion when a specialist question exists. MRI assesses neural structures, and CT depicts pars morphology and fusion or bony planning.
Age boundaries are central. The NASS adult isthmic guideline concerns adults and should not be used as a paediatric protocol. POSNA’s paediatric position material describes extension-related back pain, hamstring tightness and possible radiculopathy and supports activity modification and rehabilitation for many low-grade symptomatic pars lesions, with specialist oversight for progression or high-grade disease. Adult degenerative management overlaps lumbar stenosis: non-operative care first when stable, then specialist decompression and possible fusion according to neural compression, instability, foraminal disease, deformity and informed preference.
Key points
- Spondylolisthesis is translation of one vertebra relative to another. Degenerative slip usually affects older adults at L4–5 with intact pars; isthmic slip follows a pars defect, often at L5–S1 and may arise during growth.
- A slip can be incidental or cause extension-related back pain, radiculopathy, neurogenic claudication or deformity. Symptoms and neurological findings—not grade alone—set clinical urgency.
- Keep age-specific pathways separate: an adolescent athlete with pars stress injury is not managed by an adult degenerative-stenosis algorithm, and the adult NASS isthmic guideline explicitly excludes paediatric patients.
- Use standing lateral radiographs to quantify slip and alignment; MRI evaluates roots and canal when neurological symptoms exist, while CT best defines pars bone anatomy for selected questions.
- Initial stable care is diagnosis-specific activity modification, education and rehabilitation. Persistent disabling concordant neural symptoms or progression prompts specialist surgical assessment rather than automatic fusion for every radiographic slip.
- In adult degenerative spondylolisthesis with symptomatic stenosis, the 2025 AO Spine review supports individualised selection: both decompression alone and decompression plus fusion can be considered, with imaging assessed for instability. If applying the narrower 2014 NASS decompression-alone exception, it requires symptomatic single-level low-grade (<20%) slip without lateral foraminal stenosis and preservation of midline structures.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Degenerative
Facet and disc degeneration permit translation with the pars intact, typically at L4–5 in older adults and often with canal stenosis.
Isthmic
A pars stress lesion, elongation or defect permits translation, commonly at L5–S1; presentation spans adolescence and adulthood.
Other causes
Dysplastic anatomy, acute fracture, destructive tumour or infection and iatrogenic destabilisation require distinct cause-specific emergency or specialist pathways.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Translation and load
Altered facet-disc mechanics can generate axial pain and change foraminal or central canal dimensions under load.
- 2Neural compression
Degenerative slip often narrows the canal or recess, while isthmic slip and disc-height loss may compromise the exiting foramen.
- 3Growth-related progression
In skeletally immature patients, slip behaviour and deformity risk depend on growth and lumbosacral anatomy, requiring paediatric expertise.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Usually occurs with an intact pars and degenerative facet-disc change, commonly at L4–5. Presentation may be mechanical pain, neurogenic claudication or root symptoms in an older adult.
A pars interarticularis defect permits translation, commonly at L5–S1. An adolescent may report extension-related pain; an adult may develop foraminal L5 radiculopathy as disc height falls.
Radiographic translation without concordant pain, deficit or progression is an anatomical observation. Avoid converting it automatically into a surgical diagnosis.
Growth remaining, higher-grade slip, abnormal posture, hamstring spasm, neurological symptoms or documented progression warrant paediatric spinal specialist assessment.
New sacral dysfunction or rapidly progressive weakness requires emergency evaluation independently of the known chronic slip.
Major trauma, destructive bone change, systemic illness or cancer risk suggests fracture, infection or tumour rather than routine degenerative or pars disease.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Standing anteroposterior and lateral lumbar radiographsFirst step - Why
- Confirm translation under load, identify level, estimate Meyerding grade and assess alignment.
- Interpretation and limitations
- Describe percentage slip and overall alignment. Grade alone neither proves symptoms nor determines fusion; compare prior studies when progression is the clinical question.
- 02
Flexion–extension lateral radiographs - Why
- Assess dynamic translation when instability would change specialist planning.
- Interpretation and limitations
- Apparent motion depends on technique and pain-limited effort. These are targeted planning views, not mandatory routine imaging for every incidental low-grade slip.
- 03
Lumbar MRI - Why
- Define central, lateral-recess and foraminal neural compression when radiculopathy, claudication or surgery is being assessed.
- Interpretation and limitations
- Match side and root. Degenerative L4–5 slip often contributes to central or recess stenosis; isthmic L5–S1 disease can compromise the exiting L5 foramina.
- 04
Thin-section CT - Why
- Characterise pars bone anatomy, traumatic lesions or fusion status when the answer affects specialist treatment.
- Interpretation and limitations
- CT is excellent for cortical bone but adds ionising radiation and does not replace MRI for neural tissues; this is particularly important in young people.
- 05
MRI for adolescent pars stress response - Why
- Evaluate active marrow stress and alternative pathology without ionising radiation when clinically selected.
- Interpretation and limitations
- A stress response may precede a clear cortical defect. Imaging strategy is age- and expertise-dependent and should minimise unnecessary radiation.
- 06
Targeted laboratory or oncological studies - Why
- Investigate infection, inflammatory or malignant causes when systemic features or destructive imaging are present.
- Interpretation and limitations
- An abnormal slip morphology with systemic context is not simply “degenerative”; pursue the causal diagnosis urgently.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Non-specific axial low-back pain
Common pain may coexist with an incidental low-grade slip; clinical concordance and functional assessment prevent unnecessary structural over-treatment.
Lumbar disc herniation
An acute root syndrome may arise from a separate disc lesion rather than translation or foraminal loss.
Hip or sacroiliac disease
Joint-provoked groin, buttock or rotational pain may better explain symptoms and disability than the lumbar radiographic finding.
Pathological instability
Infection, tumour or fracture is suggested by systemic features, destructive anatomy or trauma and changes urgency.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Adult symptomatic-slip pathwayStable adult degenerative or isthmic spondylolisthesisFirst stepAn adult has concordant mechanical, radicular or claudicant symptoms without emergency neurological compromise.+
- 1Classify the slip and clinical syndrome, explain that radiographic grade alone does not mandate surgery, and begin diagnosis-specific activity, exercise and functional rehabilitation with medicine-risk review.
- 2If disabling symptoms persist, obtain standing and management-changing cross-sectional imaging and refer for specialist correlation of neural compression, dynamic instability, deformity, comorbidity and goals.
- 3For adult degenerative slip with symptomatic stenosis, individualise decompression alone versus decompression plus fusion. AO Spine 2025 concludes that mixed randomized and meta-analytic evidence does not support a blanket choice and advises assessment for instability. The narrower 2014 NASS exception reports equivalent outcomes for decompression alone only in symptomatic single-level low-grade (<20%) slip without lateral foraminal stenosis when midline structures are preserved.
- 4For adult low-grade isthmic slip with persistent concordant symptoms, determine the pars, disc, foraminal and alignment pain generators before selecting decompression, fusion or combined reconstruction.
- 5EscalationContinue rehabilitation and monitor neurological function after either non-operative or operative treatment; reassess rather than escalating solely because the slip remains visible.
02Young-person pathwaySuspected pars stress injury or isthmic slip during growthA child or adolescent has extension-related back pain, hamstring tightness, deformity or a pars lesion.+
- 1Refer through an age-appropriate musculoskeletal or paediatric spinal pathway, restrict the provoking high-load extension activity and assess neurology, growth, grade and progression.
- 2Use rehabilitation focused on pain-free motion, trunk control and gradual return; specialist imaging and any bracing or surgery are chosen by age, healing potential, slip severity and progression rather than adult degenerative guidance.
- 3Follow symptoms, neurological status, posture and radiographic progression through growth, bringing review forward for any deterioration.
03Emergency instability pathwayNew neural deficit, major trauma or destructive featuresA person with a known or suspected slip develops cauda equina symptoms, rapid weakness or evidence of traumatic or pathological instability.+
- 1Activate the appropriate emergency cauda equina, trauma, infection or malignant-compression pathway and protect the spine when instability is possible.
- 2Obtain urgent specialist imaging matched to the emergency and document serial motor, sensory and pelvic-organ findings.
- 3Involve spinal surgery promptly for confirmed neural compression or instability while treating infection, malignancy or trauma-specific physiology in parallel.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Oral NSAID
For an appropriate adult, use the selected product at the lowest effective dose for the shortest necessary period.Assess gastrointestinal, renal, hepatic and cardiovascular risks, pregnancy and interactions; consider gastroprotection and monitoring. Paediatric prescribing requires an age-appropriate product and clinician and is not inferred from adult NG59.
Opioid or sedating neuropathic medicine
Avoid automatic chronic escalation; if already used, review indication, measurable benefit, adverse effects and withdrawal needs.Sedation, falls, impaired driving, constipation and dependence may be especially harmful. Follow the applicable indication-specific guidance rather than extrapolating a dose across adult and paediatric populations.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Progressive deformity
Higher-grade or progressive slip can alter sagittal balance, posture and walking mechanics, particularly during periods of remaining growth.
Radiculopathy or claudication
Foraminal, recess or central narrowing can produce persistent neural pain, weakness, sensory disturbance and substantial walking limitation.
Cauda equina dysfunction
Severe acute neural compromise is uncommon but demands immediate assessment when pelvic-organ or saddle symptoms occur.
Adjacent or operative morbidity
Fusion and decompression can cause neural, dural, infectious, non-union or adjacent-segment complications that require informed consent.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Track pain with walking, sport, work and daily function, and repeat root and sacral neurological examination when symptoms change.
- In a growing person, specialist follow-up considers remaining growth, posture, slip percentage and progression rather than using an adult interval.
- For non-operative adult care, reassess whether symptoms remain concordant with the slip or are better explained by hip, vascular, neuropathic or axial pain.
- After surgery, monitor wound, motor and sensory recovery, alignment and fusion as appropriate, with urgent review for fever, new deficit or pelvic-organ symptoms.
- Review medicine toxicity and dependence and maintain conditioning; radiographic persistence without clinical worsening is not alone treatment failure.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Pars and level
An L5 pars defect permits L5 to translate on S1 and can narrow the L5 foramen; do not confuse the vertebral slip level with the symptomatic root.
Grade is descriptive
Meyerding grade quantifies translation but does not encode symptoms, instability, slip angle or neurological urgency.
Loaded imaging matters
Supine MRI can underrepresent translation seen when standing, while MRI better answers the neural-compression question.
Two adult entities
Degenerative and adult isthmic slips differ anatomically and have separate NASS guidelines; neither is a paediatric protocol.
11Common pitfallsFrequent interpretation and management errors.
- 01
Using a radiographic slip grade as a stand-alone indication for fusion.
- 02
Applying adult degenerative guidance to an adolescent with an active pars stress injury.
- 03
Missing foraminal L5 compression in an L5–S1 isthmic slip because attention remains on central stenosis.
- 04
Ordering repeated ionising imaging in a young person without a management-changing question.
- 05
Attributing acute cauda equina symptoms to a known stable slip and delaying emergency assessment.