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The Spine Blog

Friday, May 17, 2019

Tricortical iliac crest was the original bone graft used for ACDF, and it has excellent structural and biological properties. It is osteoconductive, osteoinductive, and osteogenic and had a stiffness similar to the vertebral bodies. Unfortunately, harvesting the iliac crest is a potentially morbid procedure that can be complicated by pain or infection. Additionally, it takes up valuable time in the operating room. Given these concerns, surgeons transitioned to the use of allograft and subsequently PEEK cages. Recently, other bone graft substitutes such as BMP, ceramic-based synthetics (CBS), mesenchymal stem cells (MSC), and bone marrow aspirate (BMA) have come into use without much evidence regarding their efficacy. In order to better understand the effectiveness of the various bone graft substitutes, Dr. Stark and colleagues from Texas performed a systematic review to compare fusion rates across the various bone graft substitutes. They included all studies that evaluated one or two level ACDF performed for degenerative conditions and had at least 6 months of radiographic follow-up with either x-ray or CT scan to evaluate fusion status. They determined the mean fusion rates across studies for the various bone graft substitutes and combinations of substitutes. All studies including BMP reported 100% fusion rate, though this product was also associated with the highest dysphagia rates (85% for 3 studies using BMP+PEEK cages and 58% for BMP+structural allograft). Ten studies used allograft alone and had a mean fusion rate of 87%, though this increased to 94% when one outlier study reporting a rate of 35% was excluded. Structural allograft or a PEEK cage combined with MSCs resulted in fusion rates around 90%. The lowest fusion rates were seen for CBS alone, with a mean fusion rate of 81%.

The authors have done a nice job reviewing and synthesizing the highly variable literature on this topic. This paper shares the same limitations with all systematic reviews, namely that the quality of the data is only as good as the papers that were included. The main limitation is that every study had its own definition of fusion, which could vary in terms of duration of follow-up, use of radiograph or CT scan, or specific criteria used to determine fusion. The patient populations were also likely quite variable in terms of characteristics that could affect fusion rate such as proportion of smokers and diabetics. The products were also used in many combinations, and the authors did not separate structural allograft from demineralized bone matrix in the analysis. Despite these limitations, the data is fairly convincing that allograft alone yields fusion rates at least as high as the other options, with the exception of BMP. The authors noted the complications associated with BMP use in anterior cervical surgery, but they did not go so far as to discuss that BMP is essentially contra-indicated in anterior cervical surgery and is rarely if ever used at this point. The CBS products had the lowest fusion rates, likely due to their complete lack of osteoinductivity. Given the relatively good fusion rates with allograft alone, the authors concluded that there is no evidence to support adding products such as MSCs or CBS to allograft. Structural allograft is easy to use, results in high fusion rates, and is inexpensive, so the authors conclusions appear valid despite the relatively low quality of the studies they were able to include in their analysis. For patients at risk for pseudarthrosis such as smokers and diabetics, the ideal bone graft remains undefined.

Please read Dr. Stark's article on this topic in the May 15 issue. Does this change you view on bone graft substitutes for ACDF? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS
Associate Web Editor


Saturday, May 11, 2019

Surgery for lumbar radiculopathy or claudication is generally elective and done to alleviate pain and improve function. The decision to undergo surgery is related to how the patient and surgeon perceive the likely risks and benefits associated with the operation. While it is impossible to perfectly predict outcomes with surgical and non-operative treatment, patients can be advised on the probability of outcomes and complications as well as the typical recovery periods. Prior literature has suggested that patients retain only a small portion of the information conveyed to them at an office visit and oftentimes do not comprehend even relatively basic concepts pertaining to their condition, planned treatment, and likely outcomes. In order to better understand the decision-making leading up to lumbar decompressive surgery, Dr. Rehman and colleagues from McMaster University in Ontario performed a qualitative study in which they interviewed 12 patients after the decision was made to undergo surgery and before they underwent the operation. They also interviewed their six surgeons. Using inductive content analysis, they classified the content of the interviews into broad themes and compared patient and surgeon experiences around the decision-making process as well as their expectations. The authors documented that the patients had relatively limited recall about their condition, treatment, and recovery. The surgeons also felt that patients had a relatively limited understanding despite their efforts to convey information using aids like spine models and MRI images. Patients also believed that decompressive surgery would improve both their leg and back pain, while the surgeons were adamant that they informed patients that only their leg pain was likely to improve. While all patients went through a consent process in which risks were discussed, they tended to remember only serious—and very rare—complications such as paralysis. Patients tended to consult family, friends, and the internet to gather more information, accurate or not. They reported making the decision to proceed with surgery based on the severity of their symptoms and not a careful calculation regarding the risks and benefits of surgery.

The authors have done a nice job performing a qualitative study on a topic that can probably only be studied using such methods. Efforts to evaluate the decision-making process using validated outcome measures such as decisional conflict scales would have likely missed much of the content that was captured with the qualitative approach. The results of this study come as no surprise to surgeons who go through this process with patients on a daily basis. Patients generally arrive in a state of distress and are simply looking for a way to relieve their pain. While shared decision making experts extoll the virtues of an arithmetic calculation based on likely risks, benefits, and ultimate utility of surgery, such a process is foreign and unsatisfying to most patients. Many patients want a surgeon to recommend the treatment most likely to help them and expect that the surgeon has done the "calculations" behind such a recommendation. There is a subset of patients who do engage in the traditional, semi-quantitative shared decision-making process, and surgeons need to be able to judge their patients in terms of what type of decision support they require. The current paper did not record and analyze the actual content of the office visit at which the decision to proceed with surgery occurred, and that could have added some more objective data about what was conveyed and what was absorbed. Those details may actually matter little, as patient perceptions and expectations are what shape satisfaction with outcomes. Even if the surgeon did an excellent job explaining the condition, planned treatment, and likely outcomes, if the patient did not understand or retain the information, it will not shape their expectations or satisfaction. Studies such as these should serve as good reminders to surgeons that patient expectations may not be realistic, and multiple conversations before and after surgery are likely necessary to bring their expectations in line with reality.

Please read Dr. Rehman's article on this topic in the May 15 issue. Does this change how you view the surgeon's role in setting patient expectations? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS
Associate Web Editor


Friday, May 3, 2019

Frailty has received much attention in the medical literature recently, and multiple spine surgery publications have reported that it is a risk factor for complications. Given that frailty indices take into account comorbidities, disability, and limited physiological reserve, this finding comes as no surprise. A more interesting question is whether or not frailty is modifiable. In order to better assess that question, Dr. Yagi and colleagues from Japan analyzed a prospectively collected database of 240 patients undergoing major surgery (average of 10 vertebral levels fused) for adult spinal deformity (ASD). Based on the medical record, they classified the patients as robust, prefail, or frail using the modified frailty index. As expected, the complication rate was higher for the frail groups. The novel aspect of this study is that the authors assessed how well the comorbidities contributing to frailty were under control. For example, in diabetic patients they determined if the hemoglobin A1C was less than 7% and, in hypertensive patients, they determined if blood pressure was less than 180/110. They classified patients whose comorbidities were being appropriately managed according to guidelines as those with good control of frailty, and those that were not being managed well as having poor control. The average age of their cohort was 58, and 92% were women. Fifty-nine percent were classified as robust, 34% prefrail, and 7% frail. After combining the prefrail and frail patients, they found that 72% had good control, and 28% had poor control of frailty. The prefrail and frail patients had worse baseline and two-year sagittal imbalance and SRS-22 scores. These patients also had a higher rate of complications. When comparing outcomes between patients with good and poor control of frailty, there were no significant differences in radiographic outcomes, SRS-22 scores, or complication rates. The poor control patients had a 26% increase in the odds of a complication compared to the good control group, though this was not statistically significant. The authors concluded that good control of frailty did not improve outcomes.

The authors have addressed a novel question and concluded that frailty is not a modifiable risk factor. Before accepting this conclusion, the study limitations need to be considered. For one, the number of poorly controlled patients is relatively low (n=27), and it is likely that the study was somewhat underpowered to detect differences between the good and poor control groups (for example, a 26% increase in the odds of a complication in the poor control group was not significant). Additionally, the authors did not assess whether or not efforts were actually made to treat the comorbidity, just whether or not the comorbidity was being controlled sufficiently according to guidelines. It is possible that patients with borderline diabetes were classified as having good control even though they just had mild disease, while some patients with brittle disease who were being treated aggressively were simply unable to meet the guidelines for being considered controlled. To truly answer the question about whether or not frailty is modifiable, patients would have to be randomized to an aggressive program to treat frailty pre-operatively vs. usual care. The current study supports the prior literature that shows frailty is associated with worse outcomes. While it raises the question of whether or not frailty is modifiable, I do not think it offers sufficient evidence for us to give up our efforts to optimize our patients pre-operatively.

Please read Dr. Yagi's paper on this topic in the May 15 issue. Does this change how you view the role of frailty in surgical decision making? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor


Friday, April 26, 2019

Cervical disc arthroplasty (CDA) has been available in the United States for over a decade. However, it has not been widely adopted despite multiple IDE RCTs that have reported better results than ACDF. Dr. Lavelle and colleagues published the 10 year follow-up data on the RCT comparing the BRYAN cervical disc to ACDF for single level pathology in the May 1 issue. Over 450 patients were originally randomized to either CDA or ACDF using an anterior plate and allograft, and approximately 50% were available for 10 year follow-up. At enrollment, the average age was 45, all patients had radiculopathy or myelopathy, and patients with significant spondylosis, collapsed disk space, kyphosis, or facet arthropathy were excluded. The primary endpoint was "overall success", which required a greater than 15 point improvement on the Neck Disability Index (NDI), no decline in neurological function, no serious adverse events related to the implant, and no subsequent surgery at the index or adjacent levels. At 10 years, 81% of CDA patients and 66% of ACDF patients achieved "overall success" (p=0.005). The CDA group also improved about 7 points more on the NDI (38 points vs. 31 points, p=0.01). Neck and arm pain VAS scores also favored CDA, though the differences were not significant. The authors did not report the overall reoperation rates for the two groups, though they noted there was a trend towards a lower reoperation rate for adjacent segment disease in the CDA group (10% vs. 16%, p=0.15). They reported 6 reoperations for pseudarthrosis in the ACDF group and 3 device removals in the CDA group related to implant complications. The serious device-related adverse event rate was 4% for the CDA group and 5% for the ACDF group.

This study represents some of the best long-term data available on CDA. The results were similar to the short and medium term studies that showed modest benefits for CDA compared to ACDF. Like most long-term studies, this one is limited by loss to follow-up, which puts the study at risk for attrition bias. However, loss to follow-up was similar for the two groups, and it seems unlikely that those lost to follow-up were markedly different for the two treatment groups. The authors could have supported this hypothesis by analyzing the characteristics of the patients lost to follow-up in each group. They could have more clearly reported the reoperations in each group, as it is somewhat hard to determine the overall reoperation rates from the data provided. A major question about CDA is why it has failed to gain popularity despite promising trial results. The inclusion and exclusion criteria used in this study may explain the low rates of adoption. The enrolled patients were young, had single level disease, and no significant spondylosis. The vast majority likely had acute, soft disk herniations. This type of patient is relatively rare in most spine practices, with the majority of radiculopathy and myelopathy patients presenting with multilevel spondylosis with central and foraminal stenosis due to disk osteophyte and uncovertebral hypertrophy. These patients would not have been included in this study, and most surgeons consider that type of pathology a contra-indication to CDA. It may be that most spine surgeons do not see enough patients who are appropriate candidates for CDA to dedicate the time and energy to learning the technique and progressing along the learning curve required for its use. There is also concern about the very long-term outcomes for these devices, given that they tend to be indicated in relatively young patients. In this study, the average patient will likely live an additional 35 years or more, and it is unclear what will happen to these devices over decades. Most total joint replacements have a substantially shorter lifespan than the patients in this study. Finally, the advantages of CDA are relatively modest compared to ACDF, even in the highly selected populations enrolled in the industry-sponsored IDE trials. The patient reported outcomes are similar for CDA and ACDF, and the decrease in adjacent segment disease is relatively minor. While CDA does seem safe and effective, it is unclear if it will ever be widely adopted.

Please read Dr. Lavelle's article on this topic in the May 1 issue. Does this change your views about cervical disc replacement? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor


Sunday, April 21, 2019

Intraoperative neuromonitoring (IONM) is frequently used during high-risk spinal procedures and has been shown to be beneficial in spinal deformity surgery. The literature has demonstrated that neurological dysfunction due to spinal cord and nerve root compression resulting from correction maneuvers can be detected and is frequently reversible. Less is known about the benefits of IONM in other high-risk procedures such as decompression of OPLL and resection of spinal cord tumors. In an effort to better understand when IONM can help prevent neurological injury—as opposed to simply alerting the surgeon to an irreversible event—Dr. Yoshida and colleagues from multiple institutions in Japan evaluated IONM reports and neurological outcomes in over 2,800 patients undergoing high-risk spine surgery. Cases were classified as deformity correction, decompression of cervical and thoracic OPLL, and treatment of intramedullary and extramedullary spinal cord tumors. The IONM reports were classified as true positives, false positives, true negatives, and false negatives based on the conclusions of the monitoring team at the end of the case and the neurological exam on post-operative day number one. They also classified cases as "rescues" when there was an IONM alert indicating at least a 70% amplitude loss of transcranial motor evoked potentials (Tc-MEPs) that then recovered by the end of surgery. Overall, the alerts had a sensitivity of 93%, a specificity of 91%, a positive predictive value of 35%, and a negative predictive value of 99.6%. The low positive predictive value resulted from the relatively low number of true positive alerts compared to false positive alerts. They calculated the rescue rate as 52%, defined as the number of alerts that resolved by the end of the case and had no post-operative neurological deficit divided by these "rescue" cases plus the true positive cases. The rescue rate varied substantially across the different diagnoses, from 82% for cervical OPLL to 32% for intramedullary spinal cord tumor. Deformity had the second highest rescue rate at 61%. Reversing the rod rotation in deformity correction was associated with a rescue rate of over 70% compared to only 40% for reversing a 3-column osteotomy. Alerts occurring during OPLL decompression were also associated with low rescue rates (0% during corpectomy for cervical OPLL and 30% during posterior decompression for thoracic OPLL).

This study is likely the most detailed analysis of IONM alerts and the effects of various interventions on reversing potential neurological damage. The authors did an incredible job assembling a large number of high-risk cases and then doing a deep dive into the IONM reports and post-operative neurological exams for each patient. The most significant limitation of the study is that it is not possible to determine how many patients were truly "rescued" by the intra-operative maneuvers following the alerts as there is such a high false positive rate associated with IONM. Additionally, the actual number of each type of alert (i.e. signal loss during rod rotation) for each diagnosis gets relatively low despite starting with nearly 3,000 cases, so it is hard to draw strong conclusions when there are just a handful of many alert types. The authors also did not evaluate other IONM modalities such as somatosensory evoked potentials or D wave. Nonetheless, this is an extremely detailed analysis IONM during high-risk cases. Use of IONM is standard of care for deformity surgery and spinal cord tumor surgery, though its benefit in myelopathy cases can be debated. While rescue rates were relatively low for certain events in the OPLL cases, there were some reversible deficits that corrected with posture changes or additional decompression. What was missing from the paper was an analysis of the deleterious effects of false positive alerts,  including unnecessary maneuvers, prolonged surgery or case abandonment. This paper suggests that IONM frequently yields alerts that prompt a maneuver that appears to prevent neurological deficit and supports its use in these high-risk cases. The jury remains out on its benefit in lower risk cases.

Please read Dr. Yoshida's article on this topic in the April 15 issue. Does this change how you view the benefits of IONM in high-risk spine surgery? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor