Degenerative Spondylolisthesis

What it is. Degenerative spondylolisthesis is a disorder of segmental instability in which a vertebra slips forward on the one below through progressive degeneration of the facet joints and the intervertebral disc, with an intact pars interarticularis. The intact pars is the definition and the whole distinction from isthmic spondylolisthesis, in which the pars is defective; because the neural arch remains intact the condition is sometimes termed "pseudospondylolisthesis". It is a failure of the "three-joint complex", the disc and the two facet joints, to maintain alignment under load, and it rarely exceeds Grade II.

Who. The classic patient is a woman over 50 with a slip at L4-5. In the community-based Framingham cohort imaged with CT, prevalence rose progressively from the fifth through the eighth decades of life (Kalichman 2009); peak incidence is 50-70 years, and the condition is extremely rare under 40. It is reported more frequently in Black women in North American population studies.

Why women. Large population data show a male-to-female ratio of approximately 1:3 (Kalichman 2009), and surgical and clinical series often quote a higher female predominance, up to about 5:1. The difference is attributed to ligamentous laxity, smaller facet joints and post-menopausal hormonal effects on connective tissue.

Where. L4-5 in about 80% of cases, L4 slipping forward on L5: this is the most susceptible level because it sits at the transition between the mobile lumbar spine and the stable lumbosacral junction. L3-4 is the second most common level. L5-S1 is rare, for the reasons given in the anatomy below.

Risk factors. Alongside age and female sex:

• Sagittally oriented facet joints, which permit forward translation
• The post-menopausal state, with its reduced ligamentous restraint
• Diabetes, which accelerates disc and facet degeneration
• A high pelvic incidence, associated with both the presence and the severity of the slip
• Multiple pregnancies, which may contribute through abdominal muscle stretching and hormonal laxity

The facet joint. The zygapophysial joint is a synovial joint formed by the superior articular process of the level below and the inferior articular process of the level above. Its capsule is richly innervated, by the medial branch of the same level and of the level above, which makes it the source of facetogenic pain. Lumbar facets are predominantly sagittal and permit flexion and extension, where thoracic facets are coronal and permit rotation; within the lumbar spine the L5-S1 facets are more coronally oriented and resist anterior shear, whereas the L4-5 facets are more sagittal and susceptible to it.

The ligaments. The iliolumbar ligament runs from the L5 transverse process to the ilium and stabilises L5 on the sacrum. Together with the deep seating of L5 in the pelvis below the intercristal line, that is why degenerative slips at L5-S1 are rare. The ligamentum flavum, the elastic yellow ligament, buckles anteriorly into the canal as the disc collapses and contributes to the stenosis alongside facet hypertrophy.

The roots and the vessels. The L4 root exits below the L4 pedicle; the L5 root traverses the L4-5 disc space and is the root at risk. The aorta and vena cava lie anterior to the disc, and an ALIF at L4-5 risks the iliac bifurcation, which is why PLIF or TLIF is preferred at L4-5.

The restraints. The lumbar spine resists anterior shear through three mechanisms:

1. The disc: the annulus fibrosus provides tensile restraint against translation
2. The facets: a coronal orientation of the joint surfaces provides a bony block to anterior translation
3. The ligaments: the iliolumbar and longitudinal ligaments tether the segment

Where it fails. In degenerative spondylolisthesis the failure is primarily at the facet joints. As disc height is lost the axis of rotation shifts posteriorly and loads them, and the process that follows is the Kirkaldy-Willis cascade with a specific vector of anterolisthesis:

1. Disc degeneration. Loss of disc height and nucleus turgor reduces resistance to shear and settles the motion segment
2. Facet loading. Loss of anterior column height transfers load to the posterior elements: facets normally bear about 20% of load, and with disc degeneration this can rise toward 70%
3. Facet remodelling. Chronic loading causes cartilage wear, subluxation and effusion; the facets remodel from coronal, which resists slip, to sagittal, and once sagittal they offer little resistance to anterior shear
4. Instability. The incompetent disc and the sagittal facets allow the superior vertebra to translate anteriorly; the iliolumbar ligaments hold L5, making L4 the "victim" level above
5. Stenosis. The canal is narrowed anteriorly by disc bulge and osteophytes and posteriorly by hypertrophied facets and buckling ligamentum flavum, the "napkin-ring" effect, producing central stenosis (claudication) and lateral recess stenosis (radiculopathy)

Examiners increasingly expect the formal parameters, the fundamental equation and the PI-LL mismatch that drives modern alignment and fusion decisions.

The fundamental equation: PI = PT + SS. Because PI is fixed, any loss of sacral slope, for example with pelvic retroversion, must be matched by a rise in pelvic tilt. That is the geometric basis of the compensation seen as the slip and stenosis develop: the patient retroverts the pelvis, increasing pelvic tilt, and flexes the knees, the simian stance, to remain upright.

Pelvic incidence and lumbar lordosis must match. Lumbar lordosis (LL) should be tuned to the PI. That is also why a high PI predisposes to the slip: it demands a high lumbar lordosis to balance, and that increases the shear at L4-5.

The PI-LL mismatch. A PI-LL mismatch, commonly taken as a difference of more than about 10 degrees, signifies under-correction of lordosis and is associated with sagittal imbalance, worse patient-reported outcomes and a higher rate of adjacent segment disease after fusion. The surgical target after a lumbar fusion is therefore to restore lordosis so that PI minus LL is within about 10 degrees; the SRS-Schwab criteria add pelvic tilt over about 20 degrees and sagittal vertical axis over about 5 cm as the other alignment targets.

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Meyerding grades how far the vertebra has slipped; Wiltse classifies by aetiology.

Meyerding GradingWiltse

The grade is the percentage slip of the superior vertebra over the inferior one on the lateral radiograph.

Grade I

Slip Percentage

0 to 25%

Note

Most degenerative cases

Grade II

Slip Percentage

25 to 50%

Note

Maximum typical for degenerative

Grade III

Slip Percentage

50 to 75%

Note

Rare in degenerative (think isthmic)

Grade IV

Slip Percentage

75 to 100%

Note

Very rare

Grade V

Slip Percentage

Over 100%

Note

Spondyloptosis (vertebra falls off)

Grade	Slip Percentage	Note
Grade I	0 to 25%	Most degenerative cases
Grade II	25 to 50%	Maximum typical for degenerative
Grade III	50 to 75%	Rare in degenerative (think isthmic)
Grade IV	75 to 100%	Very rare
Grade V	Over 100%	Spondyloptosis (vertebra falls off)

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I

Aetiology

Dysplastic

Features

Congenital dysplasia of lumbosacral facets

II

Aetiology

Isthmic

Features

Lytic lesion of pars (stress fracture)

III

Aetiology

Degenerative

Features

Intact pars; facet arthritis

IV

Aetiology

Traumatic

Features

Acute fracture of hook/pedicle

V

Aetiology

Pathologic

Features

Tumour/infection weakening bone

Type	Aetiology	Features
I	Dysplastic	Congenital dysplasia of lumbosacral facets
II	Isthmic	Lytic lesion of pars (stress fracture)
III	Degenerative	Intact pars; facet arthritis
IV	Traumatic	Acute fracture of hook/pedicle
V	Pathologic	Tumour/infection weakening bone

A sixth type, iatrogenic (post-surgical, after excessive facet or pars resection at decompression), is widely taught as an addition but is not part of the original 1976 Wiltse-Newman-Macnab description. Say so if you quote it.

Neurogenic claudication is the dominant symptom, in about 90%: heaviness, fatigue or pain in the buttocks and legs on walking, relieved by sitting or leaning forward, the "shopping-cart sign". Flexion opens the canal and relieves venous congestion, which is also why static standing is often worse than walking: sustained extension load and venous engorgement.

Radiculopathy occurs in about 50%, as dermatomal leg pain. An L4-5 slip typically causes an L5 radiculopathy, the L5 root being compressed in the lateral recess.

Back pain is mechanical and lower lumbar, worse with extension (standing and walking) and relieved by flexion. Night pain may reflect instability as the muscles relax during sleep. Always rule out bladder dysfunction (cauda equina).

Examination. Inspection shows a flattened lumbar lordosis, the "flat back", a flexed posture and the simian stance, hips and knees flexed to open the canal. A step-off may be palpable: with an L4 anterior slip the L4 spinous process moves anteriorly and lies deep while L3 remains prominent, so the step is felt between L3 and L4. Extension reproduces the back and leg pain (Kemp's test), and the femoral stretch test may be positive with significant foraminal stenosis.

Neurology is directed at L5:

• Motor: extensor hallucis longus (great-toe extension) and hip abduction (gluteus medius)
• Sensory: dorsum of the foot and the first web space
• Reflexes: the ankle jerk (S1) is usually normal, and there is no reliable L5 reflex

Plain radiographs are taken standing:

• Standing AP and lateral: essential, for the slip grade and facet sclerosis
• Flexion-extension views: the stability check. Translation greater than 4mm or angular motion greater than 10 degrees defines instability, and demonstrated instability is the conventional indication to add fusion
• Spinous process view: kissing spines (Baastrup disease)

MRI is the gold standard. It measures the central canal area (critical stenosis under 75mm2): with facet hypertrophy and ligamentum flavum buckling the canal loses its normal oval shape and becomes trefoil or omega-shaped, CSF signal around the cauda equina is effaced, and the roots become crowded or redundant (serpiginous) proximal to the block.

The lateral recess is bordered by the posterior vertebral body and disc anteriorly, the pedicle laterally and the superior articular process posteriorly, and loss of perineural fat around the traversing root there signals impingement. MRI also grades the disc (Pfirrmann) and shows the facet effusion.

CT confirms that the pars is intact, since a defect makes the diagnosis isthmic spondylolisthesis; it plans the pedicle screw trajectory; and it shows facet tropism (asymmetry).

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Neurogenic versus vascular claudication. The leg symptoms are usually neurogenic claudication, but distinguishing this from vascular (arterial) claudication is a classic examiner discriminator. The cleanest discriminators are the relief posture and the pulses.

Because the two often coexist in the elderly, check the pulses and the ankle-brachial pressure index before attributing all of the leg pain to the spine.

Dural tear is commoner than in simple stenosis because of adhesions and the slip, at about 5-10%. Repair it primarily and consider flat bed rest for about 24 hours.

Implant failure, screw loosening or pull-out, is common in osteoporotic bone, which is the reason for the DEXA scan and the augmented screws above.

Adjacent segment disease. Fusion transfers load to the level above, usually L3-4. Symptomatic disease requiring further decompression or fusion runs at roughly 2-3% per year, reaching 16.5% at 5 years and 36.1% at 10 years in Ghiselli's 215-patient series. Radiographic adjacent-level degeneration is far commoner and often asymptomatic, and the two must be kept apart.

Pseudarthrosis, failure to fuse, causes loose hardware and recurrent pain. Smoking doubles the risk; NSAIDs and diabetes are the other risk factors.

Infection runs at about 1-2%, usually Staphylococcus aureus or epidermidis, and requires prompt washout.

Neurological injury. The L5 root is at risk during screw placement or reduction, and foot drop is the classic deficit.

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What to promise. Roughly 80% report a good or excellent result in case series, though that figure is soft and undefined. The reliable message, and the one patients should be told, is that leg pain and walking distance respond far better than back pain. Walking tolerance and ODI improve substantially, patient satisfaction runs at about 70-80%, and the instrumented fusion rate is over 90%.

Prognosis. Claudication as the primary symptom, single-level disease, no prior surgery and a non-smoker all favour a good result. Predominantly back pain, multi-level disease, obesity or diabetes, and a workers' compensation claim all point the other way.

Global Epidemiology

• Community-based CT imaging (Framingham, USA) shows DS prevalence rising progressively from the fifth through the eighth decades, with a male-to-female ratio of ~1:3 (Kalichman 2009).
• Surgical case series across regions consistently report L4-5 as the dominant level (~80%) and a female predominance.

Side-by-Side Society Guidance

Registry & Trial Signals

• The two 2016 NEJM RCTs (Ghogawala/SLIP and Försth/SSSS) reached opposing conclusions on routine fusion, and the usual bedside reconciliation — fuse the unstable, decompress the stable — is not supported by either trial, because SLIP explicitly enrolled stable grade I slips and still favoured fusion, while SSSS found nothing in its spondylolisthesis stratum. The differences that do separate them are case mix (SLIP was purely grade I DS; 112 of Försth's 247 had no slip at all), size (66 versus 247), and primary outcome (SF-36 physical component versus ODI). Note that on the outcome they share, ODI, neither trial found a significant advantage for fusion. The defensible position is that adding fusion buys, at most, a small quality-of-life gain at the cost of blood loss, hospital stay and money — and that it is a discussion with the patient rather than a rule.
• National spine registries (e.g. Swespine in Sweden, the UK British Spine Registry) track reoperation and patient-reported outcomes and inform the trend away from universal instrumented fusion in stable disease.

High- vs Limited-Resource Variation

• Where MRI and intraoperative navigation/fluoroscopy are limited, reliance on standing radiographs and meticulous clinical examination increases; cost and implant availability shift practice toward decompression or non-instrumented fusion.
• Implant selection (interbody cages, cement augmentation) is influenced by availability and funding, not only biomechanics.

Referral & Red Flags (universal)

• Immediate referral: cauda equina syndrome or progressive severe weakness.
• Surgical candidates: correlating MRI/dynamic-radiograph pathology after a failed 3-6 month active rehabilitation program.
• Plain standing radiographs (including flexion-extension) are the first-line screening tool; CT excludes a pars defect; MRI characterises stenosis and root compression.

Understanding Your Condition

What is a 'slip'? It is the bone (vertebra) shifting forward, not your spinal cord. This narrows the canal and pinches the nerves, causing the "heavy legs" feeling when walking.

Will it paralyse me? Degenerative spondylolisthesis rarely causes paralysis. Untreated, walking distance may gradually shrink until you are housebound.

Recovery timeline

• Hospital: ~3-5 days.
• Walking: from day 1.
• Driving: ~4-6 weeks.
• Full recovery: 6-12 months for the fusion to knit.

Red flags - go to Emergency if you experience:

• Loss of bowel or bladder control (cauda equina).
• Numbness in the saddle area (groin/buttocks).
• Leg weakness preventing walking.

1. Weinstein JN, Lurie JD, Tosteson TD, et al. Surgical versus nonsurgical treatment for lumbar degenerative spondylolisthesis. N Engl J Med. 2007;356(22):2257-2270.
2. Ghogawala Z, Dziura J, Butler WE, et al. Laminectomy plus Fusion versus Laminectomy Alone for Lumbar Spondylolisthesis. N Engl J Med. 2016;374(15):1424-1434.
3. Försth P, Ólafsson G, Carlsson T, et al. A Randomized, Controlled Trial of Fusion Surgery for Lumbar Spinal Stenosis. N Engl J Med. 2016;374(15):1413-1423.
4. Herkowitz HN, Kurz LT. Degenerative lumbar spondylolisthesis with spinal stenosis. A prospective study comparing decompression with decompression and intertransverse process arthrodesis. J Bone Joint Surg Am. 1991;73(6):802-808.
5. Chaput C, Padon D, Rush J, et al. The significance of increased fluid signal on magnetic resonance imaging in lumbar facets in relationship to degenerative spondylolisthesis. Spine. 2007;32(17):1883-1887.
6. Matsunaga S, Sakou T, Morizono Y, et al. Natural history of degenerative spondylolisthesis. Pathogenesis and natural course of the slippage. Spine. 1990;15(11):1204-1210.
7. Kalichman L, Kim DH, Li L, et al. Spondylolysis and spondylolisthesis: prevalence and association with low back pain in the adult community-based population. Spine. 2009;34(2):199-205.
8. Meyerding HW. Spondylolisthesis. Surg Gynecol Obstet. 1932;54:371-377.
9. Wiltse LL, Newman PH, Macnab I. Classification of spondylolysis and spondylolisthesis. Clin Orthop Relat Res. 1976;(117):23-29.
10. Ghiselli G, Wang JC, Bhatia NN, et al. Adjacent segment degeneration in the lumbar spine. J Bone Joint Surg Am. 2004;86(7):1497-1503.