In a patient with L5‑S1 anterolisthesis that progressed from Grade I to Grade II on standing radiographs, is lumbar microdiscectomy indicated or is transforaminal lumbar interbody fusion (TLIF) alone sufficient?

Surgical Management of Grade I–II L5‑S1 Anterolisthesis with Dynamic Instability

For a patient with L5‑S1 anterolisthesis that progresses from Grade I (supine) to Grade II (standing), transforaminal lumbar interbody fusion (TLIF) alone is the appropriate surgical intervention; lumbar microdiscectomy without fusion is contraindicated because the dynamic progression on weight‑bearing radiographs constitutes documented spinal instability requiring fusion. 1, 2

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Why Fusion Is Mandatory in This Case

Dynamic Instability Documented on Standing Films

• Progression from Grade I to Grade II on standing radiographs represents dynamic instability, which is a Grade B indication for fusion in addition to decompression 1, 2
• The American Association of Neurological Surgeons guidelines state that fusion is specifically recommended when there is documented instability, spondylolisthesis of any grade, or when extensive decompression might create iatrogenic instability 2
• Class II medical evidence demonstrates that 96% of patients with spondylolisthesis and stenosis treated with decompression plus fusion reported excellent or good outcomes, compared to only 44% with decompression alone 1, 2

Risk of Progression Without Fusion

• Up to 73% risk of progressive spondylolisthesis exists in patients undergoing decompression alone without fusion when preoperative instability is present 2, 3
• Preoperative spondylolisthesis has been identified as a main risk factor for 5‑year clinical and radiographic failure in patients undergoing laminectomy without fusion 2, 3
• Performing decompression alone when instability is present results in 73% risk of progressive slippage and need for revision surgery 3

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Why Microdiscectomy Alone Is Inappropriate

Microdiscectomy Does Not Address Instability

• There is no convincing medical evidence to support the routine use of lumbar fusion at the time of a primary lumbar disc excision for patients without significant instability; however, this patient has documented instability, making microdiscectomy alone inadequate 4
• Decompression alone is recommended for lumbar spinal stenosis without documented instability, but the presence of dynamic spondylolisthesis changes this recommendation entirely 2
• The definite increase in cost and complications associated with the use of fusion are not justified in cases lacking clear instability criteria—but this patient meets clear instability criteria with dynamic progression on standing films 4

Clinical Outcomes Favor Fusion When Instability Exists

• Patients treated with decompression/fusion reported statistically significantly less back pain (p=0.01) and leg pain (p=0.002) compared to decompression alone in the setting of spondylolisthesis 1, 2
• 93% of patients treated with decompression/fusion reported satisfaction with their outcomes, with statistically significant improvements in ability to perform activities, participate socially, sit, and sleep 2

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TLIF as the Appropriate Surgical Technique

Why TLIF Is the Gold Standard for L5‑S1 Spondylolisthesis

• TLIF provides high fusion rates of 92–95% while allowing simultaneous decompression through a unilateral approach, making it ideal for L5‑S1 pathology 4, 5
• TLIF is an appropriate surgical technique for L5‑S1 spondylolisthesis when conservative management has failed, and it offers superior biomechanical stability 4
• The combination of TLIF with pedicle screw instrumentation provides optimal biomechanical stability, with fusion rates up to 95% 4, 2

Evidence Supporting TLIF for Grade I–II Slips

• Instrumented reduction and TLIF of mid‑ and high‑grade isthmic spondylolisthesis (Meyerding grades II, III, or IV) achieved radiographic evidence of solid bony union in all but one of 10 patients with sufficient follow‑up 5
• Average anterolisthesis was reduced from 51.0% ± 16.6% preoperatively to 13.2% ± 11.8% immediately postoperative, and 17.0% ± 12.6% at final follow‑up in patients treated with TLIF and instrumented fusion 5
• Awake, endoscopic surgery for the treatment of radiculopathy in the setting of a grade I/II L5‑S1 spondylolisthesis is a viable minimally invasive treatment option—but only for patients with stable spondylolisthesis without dynamic instability on flexion‑extension radiographs 6

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Instrumentation Is Essential

Pedicle Screw Fixation Improves Fusion Success

• Pedicle screw fixation improves fusion success rates from 45% to 83% (p=0.0015) compared to non‑instrumented fusion in patients with spondylolisthesis 2
• Instrumentation with pedicle screws is appropriate to maximize fusion potential and provide immediate stability following extensive decompression 2
• Class III evidence supports pedicle screw fixation in patients with excessive motion or instability at the site of degenerative spondylolisthesis 2

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Critical Pitfalls to Avoid

Do Not Perform Microdiscectomy Alone

• Performing decompression alone in the setting of spondylolisthesis and dynamic instability may lead to progression of vertebral misalignment, recurrence of symptoms, and need for subsequent fusion surgery 2
• Decompression alone in this case could lead to progression of instability and worsening of symptoms, requiring subsequent surgery 2

Do Not Overlook Dynamic Instability on Static Imaging

• Overlooking dynamic instability on static imaging leads to inadequate surgical planning; always obtain flexion‑extension radiographs to assess for translational motion (>3–4 mm) or angulation (>10°) 3
• Paradoxical motion—where flexion causes reduction of spondylolisthesis and extension increases the anterior translation—occurs in 15% of patients with spondylolytic spondylolisthesis, and these patients may still have instability despite no anterolisthesis during flexion 7

Ensure Adequate Conservative Management First

• Comprehensive conservative management including formal physical therapy for at least 6 weeks to 3 months is required before considering fusion 4, 2
• Inadequate conservative management before surgery represents a common pitfall; ensure the patient has completed structured physical therapy, anti‑inflammatory therapy, and neuroleptic medication trials 3

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Expected Outcomes with TLIF

High Success Rates with Appropriate Surgical Technique

• Selecting the correct surgical approach—decompression + fusion when instability, spondylolisthesis, or extensive facet removal is present—results in symptom recovery in roughly 97% of patients 4
• Ninety‑three percent of patients treated with decompression/fusion reported satisfaction with their outcomes, with statistically significant improvements in functional ability and quality of life 2

Fusion Rates and Long‑Term Stability

• Fusion rates of 89–95% are achievable with appropriate instrumentation and graft materials in TLIF constructs 4, 2
• TLIF demonstrates 92–95% fusion rates with significant improvements in pain and functional outcomes when performed for appropriate indications 4

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Algorithmic Approach to Decision‑Making

1. Obtain standing or flexion‑extension radiographs to assess for dynamic instability (progression of slip with weight‑bearing or motion) 2, 3, 7
2. If dynamic instability is present (Grade I → Grade II on standing films), fusion is mandatory; microdiscectomy alone is contraindicated 1, 2
3. If no dynamic instability is present (stable Grade I slip on all views), consider endoscopic decompression alone if radiculopathy is the primary complaint and no stenosis requiring extensive facetectomy exists 6
4. For L5‑S1 pathology with documented instability, TLIF with pedicle screw instrumentation is the preferred technique 4, 5
5. Ensure 6 weeks to 3 months of comprehensive conservative management (formal PT, anti‑inflammatories, neuroleptic medications) has been completed before proceeding to surgery 4, 2, 3