Dr. Weinstein and the SPORT group deserve our appreciation for their efforts to elevate the level of evidence for spine surgery with randomized controlled trials and high-quality cohort studies. Their research has highlighted both the strengths and difficulties of performing controlled trials.
Weinstein et al. first confirmed many of the conclusions of the classic 1978 Henrik Weber trial outcomes of disc surgery for sciatica1,2. Both trials found that when imaging findings agreed with the clinically determined level of neurological compromise, candidates benefited from surgical discectomy.
The SPORT group also tackled a more difficult clinical problem when they studied the surgical outcomes and predictors of outcomes in older patients with radicular symptoms and/or neurogenic claudication related to spinal stenosis and degenerative spondylolisthesis3. The current paper's "as-treated analysis," in which the randomized and observational cohorts were combined, demonstrates that the advantages of surgical treatment that were noted at two years continued to be maintained at four years postoperatively. However, the "intent-to-treat analysis" of the randomized cohort, which was compromised by extensive crossover between treatment groups, found no significant difference in treatment outcomes at three or four years between surgically or nonsurgically treated patients.
Importantly, Deyo pointed out in a 2007 commentary that, because of the high number of crossovers, the intention-to-treat analysis in the randomized trial is likely to underestimate the benefit of surgery4. In addition, with measured and unmeasured differences between treatment groups, the combined as-treated analysis may overestimate the benefit of surgery.
The pattern of treatments employed in these studies makes it difficult to attribute treatment success to any particular surgical technique or approach. Surgical options include decompression surgery, decompression and fusion without instrumentation, and decompression and fusion with instrumentation relative to continued care. The nonoperative wings employed a broad variety of poorly defined "usual" nonsurgical treatments. The studies also lacked the power needed to facilitate a detailed subgroup analysis.
This paper and the prior one by Weinstein et al.3 may have combined distinct age groups (mean age, sixty-six years) that might not have been truly comparable. For instance, nonphysical issues and expectations differ before and after retirement age. Also, the presence of congenitally short pedicles and/or comorbidities seen in preretirement-age patients with stenosis-related radiculopathy may differ from that seen in their more elderly counterparts.
It is difficult to address the advantages and disadvantages of spinal fusion without first identifying firm indications for neural decompression alone. The outcome of the surgery for spinal stenosis in patients with spondylolisthesis is predicated on two issues. The indications for nerve root decompression are distinct from those that guide the decision to brave the additional risks of fusion, yet either set of indications can independently undermine the potential impact of the other.
The indications for decompression are predominant. In younger patients with radiculopathy, disc herniation is sufficiently common on imaging of asymptomatic subjects to require the presence of firm concordant neurological findings to help clinicians evaluate imaging studies. In older populations, anatomic changes related to spinal stenosis are even more likely to be found on imaging studies of asymptomatic subjects. Unfortunately, the process of identifying firm concordant neurological findings in patients with spinal stenosis is more daunting than it is in younger patients with disc herniation. The age-related pathogenesis of spinal stenosis is commonly associated with a gradual crescendo of symptoms for months before the patient seeks care. In comparison, elderly patients—even those who have severe radicular symptoms, distal neuroclaudication-related walking limitations, and obvious spinal stenosis—rarely have sciatic tension signs and the distinct and dramatic relative weakness, atrophy, or diminished reflexes that are commonly seen in younger patients with acute disc herniation.
The patient with spinal stenosis classically presents with a gradual, decreasing tolerance for activity, particularly walking, and symptoms are aggravated by lumbar extension, including walking downhill or down stairs. The vague clinical findings in elderly patients relegate much of the surgical decision-making to interpretation of magnetic resonance imaging studies or computed tomography scans with myelography (myelo-CT). Age-related multilevel disc-narrowing with central canal ligamentous folding, closure of foraminal neural passages, and aging facet joints—the imaging findings that are the surgical focus of the treatment of symptoms of spinal stenosis—are also imaging findings that are common at multiple levels in elderly patients without symptoms. Such indistinct clinical and imaging findings are a particular concern, given the mediocre (moderate Kappa values) agreement that was found among highly trained experts who were asked to interpret radiographic criteria for foraminal or central stenosis5.
The reported results of fusion for stenosis-related spondylolisthesis suggest either that age is an important factor affecting outcome or that the surgical indications are insufficiently rigorous. In a separate SPORT analysis, decompression with the addition of fusion was not found to be cost-effective at the time of the two-year follow-up, according to Tosteson et al.6. Further refinements of indications may enhance the presently expected outcome of three to five years of improvement after spinal stenosis surgery. Firmer indications have improved the elective surgical results associated with other spinal pathology.
Carragee et al.7 found that the results of fusion for instability, when evaluated with use of the specific Posner criteria8, were quite satisfactory as compared with the condemning outcomes found after use of "ideal discography." Surgery trial results for sciatica secondary to disc herniation suggest that a careful selection of patients and tightly defined concordant neurological and strong pathological imaging findings can reliably be associated with a speedy recovery. In contrast, multiple randomized trials of fusion for the treatment of degenerative disc disease have demonstrated disappointing outcomes9-12, in large part because of the absence of unambiguously strong clinical imaging and pathologic findings.
The study by Weinstein et al. is helpful but not definitive. It does not definitively show that the presence of age-related slippage of one vertebra upon another is alone a sufficient indication to justify the additional risks of adding fusion, with or without instrumentation, as an adjunct to decompression surgery for spinal stenosis. Further high-quality scientific efforts might corroborate the better predictors and reliable operative outcomes for patients with spinal stenosis and degenerative spondylolisthesis. Ideally, future studies might address the impact of the following:
I applaud the contributions of the SPORT researchers. They have added to the body of knowledge about the potential benefits of spinal surgery for our patients, but further work remains. More precise indications for both decompression and fusion for spinal stenosis-related degenerative spondylolisthesis remain elusive, providing an opportunity for focused research agendas. Future scientific efforts might provide sufficient power to allow for the performance of more meaningful subgroup analysis. The challenge remains to refine the surgical indications for spinal stenosis and related spondylolisthesis. The various SPORT efforts confirm the axiom that the firmer the indications, the more predictable the surgical results.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
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2. Weinstein JN, Tosteson TD, Lurie JD, Tosteson AN, Hanscom B, Skinner JS, Abdu WA, Hilibrand AS, Boden SD, Deyo RA. Surgical vs nonoperative treatment for lumbar disc herniation: the Spine Patient Outcomes Research Trial (SPORT): a randomized trial. JAMA. 2006;296:2441-50.
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