Spondylolisthesis — Wiltse Classification

Overview & Anatomy

Spondylolisthesis is the anterior displacement of a vertebra relative to the vertebra immediately below it. It is one of the most common causes of low back pain in adolescents and young adults. The term derives from the Greek `spondylos` (vertebra) and `olisthesis` (slipping). Understanding the various aetiologies, the classification system that guides management, the biomechanical factors predisposing to progression, and the surgical indications and options is fundamental to spine practice.

Anatomy relevant to spondylolisthesis: the posterior elements (pedicles, lamina, articular facets, pars interarticularis) form the `neural arch` that resists forward translation of the vertebral body; the pars interarticularis is the segment of bone between the superior and inferior articular facets — it is the weakest point of the neural arch under repetitive flexion-extension loads; failure of the pars (stress fracture) — spondylolysis — allows the vertebral body to slide forward relative to the one below; L5-S1 is the most common level (approximately 75% of cases), followed by L4-L5
Grading (Meyerding classification): the degree of slip is expressed as the percentage of the AP diameter of the inferior vertebral body by which the superior vertebra has displaced anteriorly; Grade I 0–25%; Grade II 26–50%; Grade III 51–75%; Grade IV 76–100%; Grade V (spondyloptosis) >100% — the superior vertebra has completely slipped off the anterior face of the vertebra below; Grades I–II are the most common; high-grade spondylolisthesis (Grade III–IV and spondyloptosis) carries greater risk of progressive neurological deficits and deformity

Wiltse Classification

The Wiltse-Newman-MacNab classification (1976) categorises spondylolisthesis by aetiology into five types. It is the universally accepted classification system, guiding both understanding and treatment decisions.

Wiltse Type	Aetiology	Age Group	Key Features & Notes
Type I — Dysplastic (congenital)	Congenital dysplasia of the upper sacrum and L5 neural arch; the L5-S1 facet joints are hypoplastic, rounded, or absent — they cannot resist forward translation; no pars defect — the posterior neural arch slips forward intact along with the body	Children and adolescents	Higher risk of neurological compromise because the neural arch displaces with the vertebral body (narrows the spinal canal); high risk of progression; more likely to require surgery at a young age; most patients are female; associated with sacral dysplasia
Type II — Isthmic (spondylolytic)	Stress fracture (lysis) or elongation of the pars interarticularis; the most common type requiring orthopaedic surgical management; the posterior neural arch remains behind while the vertebral body slips forward — this is why neurological compromise is LESS COMMON in isthmic spondylolisthesis than dysplastic (the canal is actually widened as the arch is left behind)	Adolescents and young adults; incidence in general population ~6%; elite athletes with repetitive extension loading (gymnasts, fast bowlers, weightlifters, divers) — up to 47% in some athletic groups	L5-S1 most common level; three subtypes: IIA (fatigue stress fracture of the pars — most common); IIB (elongated but intact pars — repeated healing of stress fractures extends the pars); IIC (acute fracture); IIA is the classic spondylolysis that progresses to spondylolisthesis in approximately 15–20% of cases
Type III — Degenerative	Long-standing facet joint degeneration and disc collapse; disc degeneration causes segmental instability → facets can no longer resist forward shear → gradual anterior translation; NO pars defect (the neural arch is intact)	Adults >50 years	L4-L5 is the most common level (contrast with isthmic — L5-S1); female predominance; associated with spinal stenosis (intact posterior neural arch + forward vertebral translation = central and lateral recess stenosis → neurogenic claudication); the `classic` cause of neurogenic claudication with antalgic posture in an elderly woman; MOST COMMON type to cause neurological symptoms (stenosis)
Type IV — Traumatic	Acute fracture of the posterior neural arch (other than the pars) — pedicle, lamina, or facet fractures; acute traumatic displacement of the vertebral body	Any age; high-energy trauma	Rare; high-energy mechanism; associated spinal cord or cauda equina injury; surgical stabilisation usually required
Type V — Pathological	Generalised or local bone disease weakening the posterior elements — Paget`s disease, osteoporosis, tumour (metastasis, primary bone tumour), infection (discitis osteomyelitis)	Any age depending on underlying condition	Uncommon; diagnosis of the underlying condition is paramount; treat the primary pathology alongside the spondylolisthesis

Spondylolysis (Pars Stress Fracture)

Spondylolysis — pars interarticularis stress fracture: the precursor to isthmic spondylolisthesis; caused by repetitive hyperextension loading of the lumbar spine (especially extension + rotation); highly prevalent in athletes — gymnasts (11%), fast bowlers (22%), divers, weightlifters; presents as activity-related low back pain, worse with extension; bilateral pars defects at L5 (the most common scenario for isthmic spondylolisthesis) allow anterior translation
Imaging for spondylolysis: plain X-rays — oblique views show the `Scottie dog` sign; the pars defect appears as a `collar on the neck of the Scottie dog`; CT scan — most sensitive for bony pars defect (gold standard for diagnosis); SPECT bone scan — most sensitive for active (metabolically active) pars stress reaction or incomplete fracture (hot on SPECT = active healing potential); MRI — detects the marrow oedema of an active pars stress reaction (STIR sequences) and rules out disc or neural pathology; CT is definitive for established pars fracture
Management of spondylolysis: activity modification (rest from sporting activities, no hyperextension); TLSO brace in slight flexion for 3–6 months (for active lesions with marrow oedema on MRI/SPECT); physiotherapy — core stabilisation and hamstring stretching; most acute spondylolysis in adolescents heals with conservative management; surgical pars repair (direct repair using a compression screw, hook-rod construct, or tension band wiring) for cases failing conservative management in young active patients with no associated disc disease; L5 pars repair is less commonly performed than L4 (L5 biomechanics less favourable); spinal fusion for cases with associated spondylolisthesis (Grade I–II) that fail conservative management

Clinical Features & Investigation

Isthmic spondylolisthesis (Type II): low back pain radiating to the buttocks; hamstring tightness (a characteristic finding in adolescent isthmic spondylolisthesis — bilateral hamstring tightness causes the typical `waddle` gait with shortened stride); neurological symptoms in high-grade slips (L5 nerve root compression from the pars defect margins or forward displacement); `step-off` palpable at the L5-S1 level in high-grade slips; physique may be characteristic (flat buttocks, lumbar lordosis, shortened trunk)
Degenerative spondylolisthesis (Type III): low back pain with bilateral lower limb neurogenic claudication (worsens with walking, relieved by sitting or forward flexion — `shopping trolley sign`); extension worsens the slip and narrows the canal; flexion reduces the slip and opens the canal; differentiate from vascular claudication (calves, not buttocks; continues at rest; no positional relief; absent pulses); associated radiculopathy (L4 nerve root most commonly affected at L4-L5 — knee extension weakness, anteromedial thigh sensation loss)
Spinopelvic parameters: high-grade spondylolisthesis (Grade III–V) is associated with specific alterations in sagittal balance and spinopelvic alignment; key parameters — (1) Pelvic incidence (PI): a fixed anatomical measurement (the angle between a line perpendicular to the sacral endplate at its midpoint and a line joining the midpoint of the sacral endplate to the axis of the femoral heads); PI is a morphological measurement that does not change with posture; (2) Pelvic tilt (PT): positional measurement; increases as the pelvis retrovertsin compensation for forward vertebral slippage; (3) Sacral slope (SS): decreases as sacrum becomes more vertical with high-grade slips; PI = PT + SS always; high PI is a risk factor for spondylolisthesis progression and recurrence after surgery

Management

Type / Grade	Non-Operative	Operative Indication	Operative Technique
Isthmic Grade I–II (low-grade)	Core strengthening, physiotherapy, hamstring stretching; activity modification; NSAIDs; most adolescents and adults with Grade I–II are managed non-operatively with satisfactory outcomes	Failed conservative management after 6–12 months; persistent significant pain or neurological symptoms; slip progression on serial X-rays; high-risk patients (young, high PI, Grade II at presentation)	Posterolateral fusion at L5-S1 (with or without pedicle screw instrumentation); PLIF/TLIF (posterior lumbar interbody fusion / transforaminal interbody fusion) for cases with disc-mediated radiculopathy; decompression of the nerve root(s) where necessary (pars defect margins may compress L5 root)
Isthmic Grade III–V (high-grade)	Limited role for non-operative treatment in symptomatic high-grade slips; activity restriction and bracing may stabilise the slip in adolescents without surgery in selected cases	Almost all symptomatic high-grade slips require surgery; neurological compromise (cauda equina or L5 nerve root); cosmetic deformity; persistent pain; progressive slip on serial X-rays	Spinal fusion ± partial reduction (partial reduction to normalise spinopelvic parameters — complete reduction not attempted due to high neurological risk); posterolateral fusion L4-S1 or L5-S1; interbody fusion to restore disc height; circumferential fixation (anterior + posterior) for maximum stability; neurological monitoring intraoperatively; L5 nerve root most at risk during reduction
Degenerative (Type III)	Physiotherapy; NSAIDs; epidural steroid injections (for radiculopathy); weight management; most patients managed non-operatively	Significant neurogenic claudication or radiculopathy not responding to conservative management; progressive neurological deficit; failed conservative treatment for ≥6 months	Decompressive laminectomy ± fusion; the SPORT trial (Weinstein et al.) showed surgery superior to non-operative management for symptomatic outcomes at 4-year follow-up; fusion reduces risk of recurrent stenosis and instability; decompression alone without fusion has higher re-operation rates in degenerative spondylolisthesis; TLIF or PLIF widely used; dynamic stabilisation devices (e.g., interspinous spacers) may be used in selected cases

Exam Pearls

Wiltse classification: Type I (dysplastic — congenital sacral dysplasia, no pars defect, neural arch slips with body — HIGH neurological risk); Type II (isthmic — pars stress fracture, neural arch left behind — LOW neurological risk); Type III (degenerative — facet OA, no pars defect, L4-L5 most common, MOST common cause of neurogenic claudication); Type IV (traumatic); Type V (pathological)
Meyerding grading: I (0–25%), II (26–50%), III (51–75%), IV (76–100%), V = spondyloptosis (>100%); most common Grades I–II; high grade = progressive risk
Isthmic vs degenerative spondylolisthesis: isthmic = L5-S1, young adults, pars defect, hamstring tightness, low neurological risk (arch left behind); degenerative = L4-L5, elderly female, intact arch, neurogenic claudication, highest neurological risk
Scottie dog sign: oblique X-ray; pars defect = collar on neck of Scottie dog; CT = gold standard for pars fracture; SPECT = most sensitive for active healing potential; MRI = marrow oedema (active stress reaction)
Dysplastic spondylolisthesis (Type I): neural arch displaces WITH the vertebral body → the spinal canal is narrowed → highest neurological risk; contrast with isthmic where the arch is left behind → canal is actually widened
Spinopelvic parameters: pelvic incidence (PI) = fixed anatomical; PI = PT + SS; high PI predisposes to spondylolisthesis; high PT = retroverted pelvis compensating for forward slip; restore PI-LL relationship in surgical correction
SPORT trial: surgery superior to non-op for degenerative spondylolisthesis at 4-year follow-up (Weinstein et al.); decompression + fusion better than decompression alone
High-grade isthmic: do NOT fully reduce (L5 root at risk during reduction); partial reduction to normalise spinopelvic parameters; circumferential fusion for stability; intraoperative neurophysiological monitoring essential
Athletes with spondylolysis: rest + TLSO brace ± physiotherapy; most heal conservatively; direct pars repair (Buck screw, hook-rod) for young athletes failing conservative care without disc disease

Spondylolisthesis — Wiltse Classification

References

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