Management of 37-Year-Old Female with Bilateral Pars Defects and Grade I Isthmic Spondylolisthesis
This patient requires surgical decompression with instrumented fusion at L5-S1 after documented failure of comprehensive conservative management for at least 3–6 months. 1, 2, 3
Surgical Indication Criteria
Bilateral pars defects with 13 mm anterolisthesis (Grade I isthmic spondylolisthesis) constitute documented spinal instability—a Grade B indication for fusion in addition to decompression. 1, 2, 3
Key Diagnostic Findings Supporting Fusion
Bilateral pars interarticularis defects represent structural failure of the posterior elements that normally resist anterior vertebral displacement, creating inherent biomechanical instability. 4, 5
13 mm anterolisthesis (approximately 25–30% slip on a standard vertebral body) confirms Grade I spondylolisthesis and documents that the instability is already producing measurable displacement. 4, 5
Moderate disc space narrowing at L4-L5 and L5-S1 indicates advanced degenerative changes that compound the instability and increase the risk of symptom progression. 4, 6
Class II evidence demonstrates that 96% of patients with spondylolisthesis and stenosis achieve excellent/good outcomes with decompression plus fusion, versus only 44% with decompression alone. 1, 2, 3
Mandatory Conservative Management Before Surgery
Before proceeding to surgery, this patient must complete a minimum of 3–6 months of comprehensive conservative therapy, including:
Formal supervised physical therapy for at least 6 weeks, focusing on flexion-based exercises (abdominal strengthening, posterior pelvic tilts) rather than extension exercises, as flexion protocols produce superior outcomes in isthmic spondylolisthesis. 1, 6
Trial of neuropathic pain medications (gabapentin or pregabalin) if radicular symptoms are present. 1
Anti-inflammatory medications and activity modification. 5, 6
Transforaminal epidural steroid injections may provide short-term relief (typically <2 weeks) but are not a substitute for structured physical therapy. 1, 5
Failure of this conservative regimen—defined as persistent disabling symptoms, functional impairment, or neurologic compromise—establishes medical necessity for surgical intervention. 1, 3
Recommended Surgical Approach
Transforaminal lumbar interbody fusion (TLIF) at L5-S1 with pedicle screw instrumentation is the appropriate technique for Grade I isthmic spondylolisthesis. 1, 3, 5
Rationale for TLIF with Instrumentation
TLIF provides fusion rates of 92–95% while allowing simultaneous neural decompression through a unilateral approach that minimizes dural retraction. 1, 3
Pedicle screw fixation improves fusion success rates from 45% to 83% (p=0.0015) compared to non-instrumented fusion in patients with spondylolisthesis. 1, 2
Interbody fusion restores disc height, improves foraminal dimensions, and places graft within the load-bearing anterior column, providing superior biomechanical stability. 1, 5
Combined anterior-posterior (360-degree) fusion achieves fusion rates of 89–95% in patients with degenerative disc disease and spondylolisthesis. 1
Bone Graft Options
Local autograft harvested during laminectomy combined with allograft provides equivalent fusion outcomes and avoids iliac crest donor-site morbidity (which occurs in 58–64% of patients at 6 months). 1
Grade B evidence supports rhBMP-2 as a bone graft extender when performing TLIF with structural interbody graft, though surgeons should use hydrogel sealant to shield the exiting nerve root (reducing radiculitis incidence from 20.4% to 5.4%). 1
Critical Decision Points: When Fusion Is Mandatory vs. Optional
Fusion Is Mandatory When:
Any degree of spondylolisthesis is present on static imaging (as in this case). 1, 2, 3
Dynamic flexion-extension radiographs demonstrate >3–4 mm translation or >10 degrees angulation, confirming dynamic instability. 2
Extensive bilateral facetectomy (>50% facet removal) is required for adequate neural decompression, creating iatrogenic instability risk of approximately 37.5%. 2
Fusion Is Not Indicated When:
Isolated foraminal stenosis without spondylolisthesis or instability is present—decompression alone (foraminotomy) achieves 97% symptom recovery. 1
Isolated disc herniation without instability—Level III evidence shows no significant difference between discectomy alone versus discectomy with fusion. 1
Expected Outcomes and Complications
Patients with isthmic spondylolisthesis treated with decompression plus fusion report:
93–96% excellent/good outcomes with statistically significant reductions in back pain (p=0.01) and leg pain (p=0.002) compared to decompression alone. 1, 2, 3
93% patient satisfaction rates with significant improvements in ability to perform activities, participate socially, sit, and sleep. 2
Complication rates for TLIF procedures are approximately 31–33.6%, including cage subsidence, new nerve root pain, and hardware issues (most not requiring immediate intervention). 1
Common Pitfalls to Avoid
Do not perform decompression alone in the presence of any degree of spondylolisthesis—preoperative spondylolisthesis is a documented risk factor for 5-year clinical and radiographic failure, with up to 73% risk of progressive slippage after decompression alone. 2
Do not proceed to surgery without documented failure of formal supervised physical therapy for at least 6 weeks—this is a critical deficiency that renders the procedure not medically necessary. 1
Do not extend fusion to L4-L5 unless that level independently meets fusion criteria (documented instability, spondylolisthesis, or anticipated iatrogenic instability from extensive decompression). 1, 2
Avoid extension-based exercise programs—flexion protocols produce superior outcomes in isthmic spondylolisthesis, with only 19% reporting moderate/severe pain at 3 years versus 67% in extension groups. 6