# Degenerative Spondylolisthesis

## Overview

Degenerative spondylolisthesis refers to the forward slippage of one vertebra on another caused by degenerative changes of the facet joints and intervertebral disc, without any defect in the pars interarticularis. This distinguishes it from isthmic spondylolisthesis, which involves a pars defect, and from dysplastic, traumatic, and pathologic forms. The condition occurs most commonly at L4-L5, accounting for approximately 70 percent of cases, and demonstrates a striking female predominance with a 6:1 ratio. Risk factors include female sex, age greater than 50, sagittal facet orientation, ligamentous laxity, diabetes, and obesity.

## Classification

### Meyerding Classification

The Meyerding system grades the degree of slip based on the percentage of displacement of one vertebral body relative to the one below. Grade I represents 0 to 25 percent slip, Grade II is 25 to 50 percent, Grade III is 50 to 75 percent, Grade IV is 75 to 100 percent, and Grade V or spondyloptosis indicates complete displacement exceeding 100 percent. Degenerative spondylolisthesis rarely exceeds Grade II, with most cases being Grade I.

| Meyerding Grade | Slip (%) | Typical Context |
|----------------|----------|-----------------|
| I | 0-25% | Most degenerative spondylolisthesis |
| II | 25-50% | Maximum for degenerative; common in isthmic |
| III | 50-75% | Isthmic (adolescents) |
| IV | 75-100% | Isthmic (severe) |
| V (Spondyloptosis) | >100% | Complete displacement |

### Distinction from Isthmic Spondylolisthesis

Several features differentiate these two conditions. Degenerative spondylolisthesis has no pars defect, occurs most commonly at L4-L5, presents after age 50, frequently causes canal stenosis because the intact posterior arch slides forward, and typically produces only Grade I slippage. Isthmic spondylolisthesis involves a pars defect, most commonly affects L5-S1, begins in adolescence or young adulthood, produces less canal stenosis because the defect effectively widens the canal, and can reach higher grades of slippage.

## Pathophysiology

The condition develops through a cascade of degenerative events. Age-related disc degeneration leads to height loss and altered load distribution across the motion segment. The facet joints undergo remodeling, developing a more sagittal orientation that permits anterior translation rather than resisting it. Ligamentum flavum hypertrophy and facet hypertrophy compound the resultant stenosis. Because the posterior arch remains intact without a pars defect, the entire posterior element slides forward with the vertebral body, directly narrowing the spinal canal. Dynamic instability may manifest as listhesis that worsens with flexion or extension. Associated spinal stenosis is present in the majority of patients who become symptomatic.

## Clinical Presentation

### Symptoms

Patients present with neurogenic claudication characterized by leg heaviness, pain, and weakness with walking, relieved by sitting or forward flexion. Low back pain is typically mechanical in nature, worsening with standing and activity. Radiculopathy develops from nerve root compression in the lateral recess or foramen, with the L5 root most commonly affected at the L4-L5 level as the traversing root. Cauda equina syndrome is rare but possible with severe stenosis.

### Physical Examination

A palpable step-off may be appreciated at the involved level corresponding to the anteriorly displaced spinous process. Lumbar extension is often limited and may reproduce symptoms. The neurological examination is frequently normal at rest but may become abnormal after a provocative walking test. Hip range of motion and vascular status should be evaluated to exclude alternative diagnoses.

## Diagnostic Imaging

### Standing Radiographs

AP and lateral radiographs in the standing position are essential for measuring the degree of slip. Standing views are critical because supine imaging may underestimate the slip by 5 to 10 millimeters. Flexion-extension lateral views assess dynamic instability, with more than 3 to 5 millimeters of translation considered significant. Sagittal alignment and pelvic parameters should also be evaluated.

### MRI

MRI assesses the severity of stenosis, disc degeneration, and facet arthropathy. It demonstrates nerve root compression in the lateral recesses and foramina and excludes other pathology such as tumor or infection. T2 signal changes in facet joints may suggest active inflammation.

### CT

CT confirms the absence of a pars defect, definitively distinguishing degenerative from isthmic spondylolisthesis. It evaluates bone quality for fusion planning and, when combined with myelography, provides dynamic assessment of neural compression.

## Conservative Management

Conservative treatment is appropriate as initial management for most patients with mild to moderate symptoms. Physical therapy emphasizing core stabilization, flexion-based exercises, and aerobic conditioning forms the foundation. Medications include NSAIDs, acetaminophen, and gabapentinoids for neuropathic pain. Epidural steroid injections provide temporary symptom relief and serve as useful diagnostic tools and bridge therapy. Bracing has limited evidence and may provide comfort without halting progression. The natural history shows that approximately one-third of patients worsen, one-third stabilize, and one-third improve over three to five years.

## Surgical Management

### Indications

Surgery is indicated for neurogenic claudication or radiculopathy significantly impacting quality of life despite three to six months of conservative care, progressive neurological deficit, cauda equina syndrome, and failure of non-operative management with documented instability.

### Decompression Alone vs. Decompression Plus Fusion

This question represents one of the most important debates in spine surgery. Arguments for decompression alone include its simplicity, shorter operative time, fewer complications, and adequacy for symptomatic relief of stenosis in stable slips. Some studies, including the Swedish Spinal Stenosis Study, showed equivalent outcomes at two years, and avoiding fusion eliminates its specific morbidities including adjacent segment disease and hardware complications.

Arguments for adding fusion are compelling. The SLIP Trial published by Ghogawala in the New England Journal of Medicine in 2016 demonstrated that decompression plus fusion was superior to decompression alone at four years for physical outcomes in patients with Grade I degenerative spondylolisthesis. The reoperation rate was significantly lower with fusion at 14 percent versus 34 percent for decompression alone. Fusion prevents progression of listhesis after destabilizing laminectomy and restores disc height and foraminal dimensions when an interbody device is used.

The current consensus favors adding fusion for Grade I degenerative spondylolisthesis with stenosis, supported by the SLIP trial data. Decompression alone may be considered in selected elderly patients with significant comorbidities, a stable slip, and high surgical risk. If decompression requires extensive facetectomy exceeding 50 percent, fusion should be added to prevent iatrogenic instability.

### Surgical Techniques

Laminectomy with posterolateral fusion and pedicle screws represents the historically standard approach. Bilateral laminectomy achieves decompression, transverse processes are decorticated and bone graft applied, and pedicle screw-rod fixation provides stabilization with fusion rates exceeding 85 percent.

TLIF, or transforaminal lumbar interbody fusion, uses a unilateral facetectomy to access the disc space for cage placement. This provides anterior column support, restores disc height, and achieves 360-degree fusion with rates exceeding 90 percent. The cage placement and rod compression can reduce the listhesis.

MIS-TLIF employs tubular retractor systems and percutaneous pedicle screws to achieve the same goals with less blood loss, shorter hospital stay, and less muscle damage, though at the cost of longer operative time, higher radiation exposure, and a steeper learning curve.

PLIF, or posterior lumbar interbody fusion, places bilateral cages through a bilateral laminectomy but requires greater thecal sac retraction and carries higher risk of nerve root injury and dural tear. It is less commonly performed than TLIF in current practice.

ALIF, or anterior lumbar interbody fusion, is rarely used as a standalone procedure for degenerative spondylolisthesis but may be combined with posterior fixation for high-grade slips or revision surgery.

### In Situ Fusion vs. Reduction

Most Grade I slips can be fused in situ without formal reduction. Reduction may improve sagittal alignment but carries risk of nerve root stretch injury. Interbody cage placement provides indirect reduction through distraction of the disc space. High-grade isthmic slips at L5-S1 represent a different clinical entity where reduction may offer more benefit.

## Outcomes

The SPORT trial demonstrated that surgery is superior to non-operative treatment at all time points for degenerative spondylolisthesis with stenosis. Fusion with decompression produces 80 to 90 percent good outcomes at two to four years. Reoperation rates are 10 to 15 percent at five years for fusion, with higher rates for decompression alone. Adjacent segment disease develops at 2 to 3 percent per year requiring intervention. Patient satisfaction surveys show 75 to 85 percent would elect surgery again.

## Complications

Pseudarthrosis occurs in 5 to 15 percent of cases, with higher rates in smokers, diabetics, and those undergoing multilevel fusion. Adjacent segment disease is the most common long-term complication. Hardware failure including screw loosening and rod breakage is more common in osteoporotic bone. Dural tear occurs in 5 to 10 percent, surgical site infection in 2 to 5 percent, and neurological injury in less than 2 percent. Medical complications in elderly patients include DVT, pulmonary embolism, urinary retention, and delirium.

<image>Lateral standing radiograph of the lumbar spine demonstrating Grade I degenerative spondylolisthesis at L4-L5 with forward slippage of L4 on L5, disc space narrowing, and facet joint hypertrophy visible on the oblique view</image>

<image>Sagittal T2-weighted MRI showing L4-L5 degenerative spondylolisthesis with associated spinal stenosis, demonstrating the forward displacement of L4, disc bulging, and compression of the thecal sac at the level of the listhesis with effacement of CSF space</image>

<image>Intraoperative fluoroscopic image during MIS-TLIF at L4-L5 showing percutaneous pedicle screws placed at L4 and L5 bilaterally with an interbody cage in the disc space, demonstrating reduction of the spondylolisthesis and restoration of disc height</image>

## Clinical Pearls

Degenerative spondylolisthesis never has a pars defect; if a pars defect is identified, the diagnosis is isthmic spondylolisthesis, which represents a different entity with different demographics and management considerations. Standing radiographs are essential because supine imaging can underestimate the degree of slip by 5 to 10 millimeters. The L4-L5 level is predisposed to degenerative spondylolisthesis because of the sagittal facet orientation at this level and because the iliolumbar ligament stabilizes L5-S1 but not L4-L5. The SLIP trial is the strongest randomized controlled trial evidence supporting fusion for Grade I degenerative spondylolisthesis and should be cited when justifying the addition of instrumentation. In elderly patients with severe comorbidities, a minimally invasive decompression alone may be the most appropriate approach, accepting the higher reoperation rate. Always obtain flexion-extension views to assess dynamic instability; a slip that worsens significantly in flexion is more likely to progress after decompression alone. BMP use in TLIF is associated with higher fusion rates but has been linked to complications including heterotopic ossification and radiculitis and should be used judiciously.

## References
1. Ghogawala Z et al. Laminectomy plus fusion versus laminectomy alone for lumbar spondylolisthesis. N Engl J Med. 2016;374(15):1424-1434.
2. Weinstein JN et al. Surgical compared with nonoperative treatment for lumbar degenerative spondylolisthesis: four-year results in the SPORT. J Bone Joint Surg Am. 2009;91(6):1295-1304.
3. Forsth P 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. Jacobsen S et al. Degenerative lumbar spondylolisthesis: an epidemiological perspective. Spine. 2007;32(1):120-125.