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The Spine Blog

Saturday, August 15, 2020

Baseline depression and anxiety are very common among spine surgery patients and are well-known risk factors for worse post-operative outcomes. There is a complex interrelationship between depression and chronic pain, and both seem to predispose to the other. Less well-studied is whether spine surgery is a risk factor for developing depression and anxiety post-operatively. To study this question, Dr. Bekeris and colleagues from the Hospital for Special Surgery used the Truven MarketScan database that includes large amounts of claims data from employer sponsored health plans across the United States. They identified approximately 39,000 patients who underwent ACDF or posterior lumbar fusion from 2012-2015 and who had data for at least a year prior to and after surgery. Approximately 16,000 had no diagnosis of or prescription for depression or anxiety for the year prior to surgery, and these patients formed the cohort of those at risk for de novo depression or anxiety post-operatively. Of these patients, 12% received either a diagnosis or prescription for depression or anxiety within 6 months after surgery, not including prescriptions for antidepressants or anxiolytics received within 1 week of surgery as those may have been part of the routine post-operative regimen. A baseline diagnosis for psychosis (less than 3% of patients had this diagnosis) was the most powerful risk factor for developing new post-operative depression or anxiety (OR 3.6). Chronic obstructive pulmonary disease (OR 1.17) was also associated with new onset depression or anxiety. Chronic opioid use either pre- or post-operatively was also strongly associated with a new diagnosis of depression or anxiety, with those starting chronic opioid use post-operatively at highest risk (OR 2.9). Lower age (OR 0.99), female sex (OR 1.35), and living in a zip code with a median household income over $60,000 (OR 1.46) were also associated with increased risk. While type of procedure (ACDF vs. lumbar fusion) and number of vertebrae fused were not risk factors, length of stay was (OR 1.08).

This is a novel study in that it identified a relatively high proportion of patients (12%) who developed novel depression or anxiety within 6 months of spinal fusion. While a high proportion of spinal fusion patients have a baseline diagnosis of depression or anxiety (59% in this study), surgeons are not generally aware of patients being at increased risk for developing these conditions de novo after surgery. This study benefits from the huge number of patients available for analysis in administrative claims databases but also suffers from the limitations inherent in this kind of study. The diagnosis of depression or anxiety relied on diagnostic coding or prescription data, not traditional psychiatric criteria for making these diagnoses. Many patients may have had depression or anxiety at baseline without a diagnostic code or prescription for the condition. Conversely, some patients not meeting the traditional diagnostic criteria for these conditions may have received a diagnostic code or a prescription. For example, many surgeons use diazepam or other benzodiazepines as muscle relaxants post-operatively, and some patients may have received prescriptions for these medications beyond the 1 week point as part of a post-operative analgesia regimen without having a diagnosis of anxiety. The reported risk factors for developing depression or anxiety post-operatively are not surprising. Opioid use is strongly associated with depression and anxiety. It is interesting that patients who started chronic opioid therapy post-operatively were at greatest risk for developing depression or anxiety. Further research would be necessary to know if the chronic opioid use predisposed them to the mental health condition or vice versa. Younger age and female sex are established risk factors for depression and anxiety. The finding of increased risk among those from zip codes with higher household income is interesting and suggests that patients with higher socioeconomic status were either at greater risk for these conditions or were more likely to seek care for them. This paper is eye opening in that it shows that spine surgery is a risk factor for new onset depression and anxiety. Surgeons and primary care physicians should be vigilant in screening for this and also do their best to avoid chronic opioid use post-operatively.

Please read Dr. Bekeris's article on this topic in the August 15 issue. Does it surprise you that spine surgery resulted in new onset depression or anxiety in over 10% of patients?

Adam Pearson, MD, MS

Associate Web Editor

Saturday, August 8, 2020

With the development of machine learning techniques to create prediction models using big data, medical researchers have started to experiment with these methods. Many studies have evaluated models predicting complications, readmissions, and patient reported outcomes in spine surgery, however, most have used traditional regression modeling techniques. Dr. Jain and colleagues evaluated two of these machine learning statistical approaches (random forest and elastic net) and compared their results to a traditional logistic regression model predicting discharge to a skilled nursing facility, 90-day readmission, and 90-day major complication rate following lumbar or thoracolumbar fusion involving at least 3 levels. They used the State Inpatient Database from North Carolina, Nebraska, New York, California, and Florida from 2005 to 2010. They identified approximately 38,000 patients undergoing long segment fusion for degenerative conditions. Thirty-five percent were discharged to a skilled nursing facility, 19% were readmitted within 90 days, and 13% experienced a major medical complication. In general, age was a powerful predictor of all adverse outcomes in all of the models. Not surprisingly, medical comorbidities were also strong predictors of all 3 outcomes. While they did not evaluate many surgical factors, an anterior-posterior approach was strongly associated with readmission and complications. Ironically, smoking was associated with lower rates of all 3 adverse outcomes. They used area under the curve analysis to assess the accuracy of the predictive models and found that logistic regression slightly outperformed the machine learning techniques. The models were most accurate in predicting discharge to a nursing facility and least accurate in predicting readmission.

This study did not reveal any new insights regarding adverse outcomes following long segment lumbar fusion surgery, namely that age, comorbidities, and larger magnitude surgery were associated with discharge to a facility, readmissions, and medical complications. However, the authors did evaluate newer machine learning statistical techniques to determine if this improved the accuracy of their prediction models. In this case, it turned out that old-fashioned logistic regression yielded slightly more accurate models. Additionally, logistic regression yields odds ratios that allow for quantitative comparison among risk factors to determine which ones are the most powerful. The machine learning techniques are designed to maximize the predictive accuracy of the model and do not provide as much information on the strength of association between each predictive variable and the outcome. Despite using newer statistical techniques, this paper shared the same limitations of all studies using large administrative databases. For one, the databases frequently do not include important outcomes such as reoperation, number of levels included in the fusion, and patient reported outcomes. In this case, looking at predictors of reoperation and being able to evaluate the effect of longer fusions would have been helpful. Additionally, miscoding can diminish the accuracy of the analysis. This paper raises the question of how these predictive models can and should be used. For more sophisticated patients, being able to accurately predict outcomes and complications based on their individual characteristics might help them in the shared decision making process. The other, more controversial use of these models is to predict the cost of the surgical episode, which a hospital system might use in deciding whether to offer to perform surgery in a bundled payment model. If the predictive model indicated that the cost of the episode exceeded the bundled payment, the hospital might decide against performing the case. Most physicians would consider this unethical. As new payment models that shift risk to hospitals and physicians are developed, we must remain aware of the perverse incentives the new systems can create.  

Please read Dr. Jain's paper on this topic in the August 15 issue. Does this change how you view the use of machine learning techniques to create predictive models using big data?

Adam Pearson, MD, MS

Associate Web Editor

Friday, July 31, 2020

Ossification of the posterior longitudinal ligament (OPLL) is a relatively common cause of myelopathy in Asian populations. While relatively rare in Western countries, it can be encountered in non-Asian patients as well. Given the higher incidence of OPLL in Asia, most of the literature on this topic is from Japan. The pathology is located anterior to the cord, however, the ossified PLL frequently becomes adherent to the dura, making resection difficult and associated with a relatively high rate of spinal fluid leak. Posterior surgery is oftentimes preferred for this reason, though a posterior approach is generally associated with a higher infection rate, higher blood loss, and more post-operative pain. In order to gain a better understanding of how anterior and posterior surgery for OPLL compare, Dr. Yoshii and colleagues from Tokyo used a Japanese administrative database to compare outcomes between OPLL patients treated with anterior and posterior decompression and fusion. They identified over 2,300 patients who underwent anterior (n=1,333) or posterior (n=1,020) decompression and fusion between 2010 and 2016. The posterior patients tended to be somewhat older and had a greater comorbidity burden. They propensity-score matched 854 pairs of patients in order to limit the effects of selection bias. After matching, there were no significant baseline differences between the two groups. They found that the anterior surgery group had a higher rate of dysphagia (2.5% vs. 0.8%), respiratory failure (1.1% vs. 0.2%), and experiencing at least one medical complication (14.5% vs. 10%). The anterior group also had a higher rate of spinal fluid leak (2.7% vs. 0.1%). The posterior group had a higher transfusion rate (12.5% vs. 7.5%), longer length of stay (33 days vs. 29 days) and a higher hospital cost ($30,700 vs. $22,800).

The authors have used a national database to create what is likely the largest cohort of OPLL patients ever assembled. Their findings that anterior surgery was associated with a higher durotomy rate is not surprising. The fact that anterior surgery was associated with a higher rate of medical complications is somewhat surprising as posterior surgery is generally considered more invasive. Higher rates of dysphagia, respiratory failure and pneumonia in the anterior group drove the differences. It is not clear how dysphagia was defined, and it is surprising that only 2.5% of anterior surgery patients were classified as having dysphagia. Given that some degree of dysphagia is essentially universal after anterior surgery, this implies that dysphagia was only coded for severe cases or that it was coded inconsistently. The in-hospital infection rate was nearly as high for the anterior group (2.7%) as for the posterior group (2.9%). In general, infection after anterior cervical surgery is very rare, less than 1% in most series. Infection after posterior surgery occurs much more commonly in most series. It is not clear why the infection rate after anterior surgery was so high in this cohort, and the authors do not comment on that. One of the drawbacks of administrative database studies is that the investigators have to accept the data on face value and cannot dig deeper into it to try to better understand unexpected findings. The findings are only as good as the quality of the coding. While some of the exact numbers are hard to reconcile and likely represent heterogeneity in coding practices across Japan, the finding of higher complication rates, especially spinal fluid leak, in the anterior surgery group is consistent with prior literature. The authors attempted to address selection bias with propensity score matching, however, the database did not contain detailed information on myelopathy severity, number of levels involved, or the presence of kyphosis. It seems as though a posterior approach is favored in most cases with neutral or lordotic alignment that can be sufficiently decompressed with a laminectomy. For kyphotic patients or those with severe anterior compression that cannot be addressed with a posterior decompression, surgeons likely need to use an anterior approach despite the risks.

Please read Dr. Yoshii's article on this topic in the August 15 issue. Does this change how you consider your approach for OPLL?

Adam Pearson, MD, MS

Associate Web Editor

Friday, July 24, 2020

The high societal cost of low back pain (LBP) has been well-documented over the years, though it is worthwhile to revisit this topic from time to time. In the United States, musculoskeletal conditions, including LBP, are the most  common cause of workers becoming disabled. In order to look at the societal costs of LBP in Spain, Drs. Alonso-Garcia and Sarria-Santamera used Spain's National Health Survey (NHS) of 2017 to calculate the prevalence of LBP, factors associated with LBP, and the direct (i.e. medical) and indirect (i.e. employment-related) costs associated with LBP. The NHS queried over 23,000 Spanish residents over age 14 and was designed to be extrapolated to the entire Spanish population. Approximately 50% of respondents were between 40 and 65 years old, with only 14% being under age 40. Overall, approximately 20% of respondents reported LBP in the past year. Female gender, age over 65, lower educational achievement (i.e. less than a high school degree), obesity, and a lack of physical activity were all associated with increased rates of LBP. Respondents reporting LBP had higher rates of physician visits, more emergency department visits, and more hospitalizations than those without LBP. Those with LBP also had more diagnostic tests, more PT visits, more psychologist visits, and more medication use compared to those without LBP. They calculated that LBP patients missed approximately 8 days of work and lost about 5 days of productivity at work due to LBP. They calculated a direct medical cost of 2.3 billion euro and an indirect employment-related cost of 6.7 billion euro, for a total societal cost of approximately 9 billion euro in 2017. This represents approximately 0.7% of Spanish GDP.

Papers like this always yield staggering numbers, and they serve as a good reminder about the social and economic costs of LBP. These analyses do not even consider the physical pain and psychological distress caused by LBP, which would add to the costs if quantified. While these studies only provide a rough-estimate of costs, they leave no doubt about the magnitude of the LBP problem. Unfortunately, little progress has been made in addressing LBP despite decades of study. The efficacy of surgery for conditions such as lumbar disk herniation and spinal stenosis has been demonstrated in the literature, however, these conditions represent a small minority of LBP cases. Axial LBP without radiculopathy or neurogenic claudication in the absence of spinal deformity is the most common type of LBP. Fortunately, most acute cases of LBP are self-limited and do not require much or any treatment. The most costly condition is chronic, axial LBP, which is generally refractory to any treatment. The underlying cause of chronic axial LBP is generally unknown, and likely involves both degenerative changes in the lumbar spine and psychosocial factors. While disability rates overall have been decreasing since the end of the great recession, musculoskeletal disability has remained high, with chronic LBP as the most common condition in this category. Given that chronic LBP is costing society as much as cardiovascular disease, diabetes, and cancer, research to address it should be getting funded at similar levels as the other conditions. Unfortunately, LBP is not a glamorous topic and receives minimal funding from national research institutions. Until that changes, we can anticipate more papers of this kind that highlight LBP's burden to society.

Please read this paper in the August 15 issue. Does this change you view the societal costs of LBP?

Adam Pearson, MD, MS
Associate Web Editor

Monday, July 20, 2020

Despite multiple randomized and observational studies demonstrating a benefit of surgery relative to non-operative treatment for spinal stenosis patients experiencing claudication or radiculopathy, a Cochrane review article concluded that there was insufficient evidence to conclude that surgery resulted in better outcomes. Some of the randomized trials were limited by crossover between the groups, and the observational studies had significant baseline differences between the two groups. These phenomenon are to be expected, and there is likely no way to prevent crossover from non-operative treatment to surgery in an RCT on this topic. In order to add further data to the literature, the Lumbar Stenosis Outcomes Study (LSOS) was designed to track outcomes following surgery or non-operative treatment for patients with lumbar spinal stenosis. This observational study included 679 patients treated at eight Swiss centers and followed them for 3 years. Approximately 60% underwent surgery within 1 year of enrollment, one third never had surgery, and 18 patients had surgery between one and three years. Not surprisingly, the surgery patients were somewhat younger, healthier, and had worse baseline symptoms and more severe stenosis at baseline. They were also more likely to report buttock or lower extremity pain and were more likely to have spondylolisthesis. Over three quarters of the surgery patients had decompression alone, and 22% had a fusion. The majority of patients had a multilevel decompression. After controlling for baseline differences, the surgery patients improved significantly more on the Spinal Stenosis Measure (SSM) symptoms and function subscales and on the EQ-5D compared to the non-operative patients, who tended not to improve much from baseline. The patients who had surgery after 1 year did not do better than the non-operative patients. There was an overall reoperation rate of 15% in the surgical group, most of which were for restenosis. The authors concluded that surgery resulted in greater degrees of improvement for lumbar stenosis patients out to 3 years.

This paper represents a high quality observational study, and the authors reasonably concluded that surgery resulted in better outcomes than non-operative treatment. The main limitation of this study, like all observational studies, is that there were baseline differences between the two groups for which the statistical analysis likely did not completely control. Given that an RCT probably cannot be performed to answer this question without substantial crossover, observational studies with good statistical analyses likely represent the best study design for this topic. While these studies do not provide ironclad Level 1 evidence, one can reasonably conclude that for patients with moderate to severe lumbar stenosis with neurogenic claudication or radiculopathy, surgery likely results in better outcomes than non-operative care. This study included a heterogeneous mix of patients with and without spondylolisthesis, and 22% underwent a fusion. The authors cast a broad net in terms of the inclusion criteria, which increases the generalizability of the study but limits conclusions about specific patient groups or surgical techniques. At this point, the Spine Patient Outcomes Research Trial, the Maine Lumbar Spine Study, and now the LSOS have provided high quality observational data suggesting that surgery improves outcomes more than non-operative treatment for spinal stenosis. Rather than performing more studies to prove this point, the spine community should focus on matching the right treatment to the right patient at the right time. Producing research that allows for evidence-based individualized care is very challenging and requires huge numbers of patients in order to perform the type of subgroup analyses necessary to answer questions at a sufficiently fine level of granularity. That is the next step for researchers focused on degenerative lumbar conditions.

Please read the article by Dr. Burgstaller in the August 1 issue. Does this change your perspective on the role of surgical and nonoperative treatment for lumbar spinal stenosis?

Adam Pearson, MD, MS
Associate Web Editor