Friday, December 9, 2016
Cervical laminectomy and fusion is a popular treatment for multilevel cervical spondylotic myelopathy. Traditionally, this has often involved a C3-C7 procedure that targets the levels with cord compression. Concerns have been raised that stopping the construct at C7 increases the risk of distal junctional failure at the cervicothoracic (CT) junction due to the significant differences in spinal stiffness between the cervical and thoracic spine. As such, some surgeons choose to extend the fusion across the CT junction to reduce the risk of distal junctional failure. While this approach may solve the distal junctional problem, crossing the CT junction may increase the risk of pseudarthrosis and hardware failure due the high forces exerted on the fusion construct. Additionally, fusion across the CT junction could lead to further loss of motion and the potential for fusing the CT junction in kyphosis, both of which could lead to patient dissatisfaction. Given that there is no strong evidence guiding surgeons on this topic, Dr. Schroeder and colleagues from Thomas Jefferson University performed a retrospective analysis of 219 patients with degenerative pathology who had undergone a multilevel posterior cervical fusion. Their primary outcome was revision rate, and no patient reported outcomes (PROs) were measured. Of this cohort, 85 had their constructs stop at C7, 104 at T1, and 30 between T2 and T4. There were no significant baseline differences between the patients, though there were trends towards an increased number of women, longer follow-up, and a higher rate of AP fusion in the C7 group. The overall reoperation rate over an average follow-up of approximately 4 years was 28%, with rates of 35% for the C7 group, 18% for the T1 group, and 40% for the T2-T4 group. These differences persisted in the multivariate regression analysis that controlled for some potential confounders, with the C7 group having over a two-fold increased risk of reoperation compared to the T1 group.
The authors have done a nice job compiling what is likely the largest study to date on this topic. However, the study design is observational and retrospective, which puts it at risk for confounding and selection bias. Another substantial limitation is that the reason for reoperation was unknown for most of the patients who underwent revision. While the limited data presented on this topic suggests that the C7 group was more prone to adjacent segment degeneration, and the T1 group had a higher rate of early hardware failure, no strong conclusions about the cause of reoperation could be made due to the high rate of missing data. The authors suggested that they controlled for surgeon in their multivariate analysis, however, the decision about the caudal level of the fusion is likely very surgeon dependent. It may be that the reoperation rate was being driven by the surgeon involved rather than the caudal level of the fusion. If there was a strong association between surgeon and caudal level selected, surgeon identify would be very difficult to control for statistically. Re-operation is also a very subjective outcome measure that depends both on surgeon and patient preference. Finally, PROs were not measured, so it is unclear if caudal level selection affected patients' symptoms post-operatively. This study certainly raises concerns about a higher reoperation rate for multilevel posterior cervical fusions stopping at C7, however, the data are not strong enough to demonstrate that overall outcomes are better if the fusion is extended to T1. A randomized trial would be necessary to answer the question definitively. Such a study would be relatively easy to design, however, it would likely require multiple study sites to generate a sufficient number of patients.
Please read Dr. Schroeder's article on this topic in the December 1 issue. Does this article convince you to extend all of your multilevel posterior cervical fusion to the thoracic spine? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor
Friday, December 2, 2016
Two recent randomized controlled trials (RCTs) comparing decompression alone to decompression plus posterolateral fusion for degenerative spondylolisthesis (DS) reached opposite conclusions, resulting in a rekindling of the debate about the role of fusion in DS.1,2 Another issue of contention is the role of interbody fusion (IF) in DS, with advocates suggesting that adding an IF results in higher fusion rates, better alignment, and indirect foraminal decompression. Potential downsides of IF include increased operative time, blood loss, rate of neurologic injury, and cost. In an effort to better evaluate the role of IF in DS, Dr. McAnany and colleagues performed a meta-analysis comparing posterolateral fusion (PLF) to IF for DS. They identified 5 high quality comparative studies on the topic, though only one randomized DS patients to PLF or IF. Quantitative meta-analysis demonstrated no significant differences in patient reported outcomes (Oswestry Disability Index, SF-36, Visual Analog Scale), fusion rate, operative time, blood loss or complications. The only significant difference in the meta-analysis was for length of stay, which was somewhat shorter in the PLF group. The results were very consistent across the different studies, and the authors concluded that there were no meaningful outcome differences between the two techniques.
The authors should be congratulated on performing such a high quality meta-analysis on this important topic. The strength of conclusions from a meta-analysis are determined by the quality of the papers included, and the included studies were all relatively good. The major limitation is that only one of the included studies was truly an RCT comparing PLF to IF, so the other studies are at risk of selection bias and confounding. Selection bias in this case would imply that surgeons were basing their treatment decisions on patient or radiographic characteristics. The Spine Patient Outcomes Research Trial (SPORT) and anecdotal experience suggest that surgeon preference (rather than patient or radiographic characteristics) is the main driver of technique selection, and this would likely minimize the effect of selection bias.3 Adding to the strength of the authors' conclusions is the consistency of the results across the different studies. Based on the individual studies and the results of the meta-analysis, it seems quite clear that there is no benefit to IF for the average DS patient. Even if the only downside of IF is increased cost, this alone should limit use of the procedure in DS given that there is no clear benefit to it. That being said, DS likely represents a spectrum of disease with varying degrees of "instability". Some patients with a very stable slip will do well with a decompression alone, while others with a high degree of instability may benefit from IF. Unfortunately, we currently do not have evidence-based methods to match DS patients to the most appropriate surgical techniques. Until we do, surgeons will continue to rely on their judgment in selecting the best operation on an individual patient level.
Please read Dr. McAnany's article in the December 1 issue. Does this change how you view the role of IF in DS? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor
1. Forsth P, Olafsson G, Carlsson T, et al. A Randomized, Controlled Trial of Fusion Surgery for Lumbar Spinal Stenosis. N Engl J Med 2016;374:1413-23.
2. Ghogawala Z, Dziura J, Butler WE, et al. Laminectomy plus Fusion versus Laminectomy Alone for Lumbar Spondylolisthesis. N Engl J Med 2016;374:1424-34.
3. Abdu WA, Lurie JD, Spratt KF, et al. Degenerative spondylolisthesis: does fusion method influence outcome? Four-year results of the spine patient outcomes research trial. Spine (Phila Pa 1976) 2009;34:2351-60.
Sunday, November 27, 2016
Proximal junctional kyphosis (PJK) and failure (PJF) are common complications following corrective surgery for adult spinal deformity (ASD). These complications are associated with worse patient reported outcomes (PROs) and are a frequent indication for reoperation. While prior studies have looked at specific risk factors for PJK, none have created a comprehensive model that predicts the risk of PJK or have evaluated the role of different risk factors in the same model. The International Spine Study Group (ISSG) sought to fill this gap in the literature by using a large database (510 ASD patients) that included patient and radiographic characteristics as well as follow-up out to 2 years post-operatively. They defined PJK as an increase in kyphosis at the proximal junctional level greater than 20 degrees compared to the initial post-operative radiograph along with an increase in the SRS-Schwab sagittal modifier grade. Proximal junctional failure was defined as a reoperation for PJK. In this population, the average age was 57, 78% were women, and the average fusion length was 12 levels. Twenty-seven percent of patients were classified as PJK/PJF (102 PJK, 37 PJF) within 2 years of their initial surgery. The most important variables predicting PJK/PJF were increasing age, lowest instrumented vertebra at the sacrum/ilium, baseline SVA > 10 cm, screws (vs. hooks) at the upper instrumented vertebra (UIV), UIV between T10 and L3, baseline PT > 30 degrees, and baseline PI-LL > 20 degrees. They used 70% of the patients to build their model, and 30% were used to test the model, which had an accuracy of 86.3%.
The ISSG should be congratulated on gathering data on over 500 ASD patients. The results provided no surprises, with increasing age, greater baseline sagittal imbalance, stopping proximally in the lower thoracic spine or distally at the sacrum/ilium, and using screws at the UIV all being known risk factors for PJK. Age is a likely surrogate for lower bone mineral density and less robust ligamentous and soft-tissue structures, and the authors noted it would have been helpful to include bone mineral density as a risk factor (it was not recorded in the database). The authors also chose to include only variables that could be considered pre-operatively. Post-operative factors such as degree of correction and residual imbalance could also play a role, though these were intentionally left out as they could not be considered during the pre-operative planning phase. This modeling strategy is novel and is different from the traditional regression modeling. In this case, many of the variables likely covaried with each other and would not have emerged as independent predictive variables in a regression model. As such, it is difficult to know how much each variable contributes to the risk of PJK, though the model's accuracy was maximized by including all of them. While the actual model could be considered for use clinically, the overall gestalt created by considering the important variables may be equally as helpful. Future models looking at other complications (i.e. infection, pseudarthrosis, hardware failure, medical complications, reoperation, etc.) and PROs would be very helpful to patients in the shared decision making process. The decision to proceed with a high morbidity surgery in a high risk population is a hard one, and having a stronger ability to predict outcomes would help patients facing this choice.
Please read Mr. Scheer's article on this topic in the November 15 issue. Does this change how you consider risk factors for PJK? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor
Friday, November 18, 2016
The role of sagittal imbalance in adult spinal deformity patients has been extensively debated and studied over the past decade, and the spine community still has not completely come to terms with how to approach it. Prior studies have shown strong correlations between sagittal imbalance and worse patient reported outcomes, though most of these studies have included both post-operative and non-operative patients.1 In order to evaluate this topic further, Dr. Chapman and colleagues from multiple spinal deformity treatment centers analyzed the correlations between sagittal radiographic parameters and patient reported outcomes in 286 patients enrolled in a study comparing surgery to non-operative treatment for adult lumbar scoliosis. Approximately 90% of the patients were women, and the average age was 60. Most patients had a relatively pronounced coronal plane deformity, with the average lumbar Cobb angle 53 degrees. Average sagittal imbalance was much milder, with the average sagittal vertical axis (SVA) within the normal range at 3.1 cm. The only sagittal parameter that was more than mildly abnormal was the pelvic incidence-lumbar lordosis mismatch, which was an average of 17 degrees. The correlations between the sagittal parameters and baseline ODI and SRS-23 scores were non-existent or weak, with the correlation between SVA and ODI being the most consistent. When patients were stratified by SVA as < 4cm, 4-10 cm, and > 10 cm, there was a significant difference between patients with an SVA < 4 cm (ODI=32) compared to those > 4 cm (ODI=40). Interestingly, there was no difference between the 4-10 cm and > 10 cm groups. In a subgroup of patients with baseline ODI > 40, the correlations between sagittal parameters and baseline patient reported outcomes were more consistent though still in the weak range.
This paper does a nice job demonstrating that sagittal imbalance likely contributes to disability in the adult lumbar scoliosis population but is probably not the main driver of symptoms. Coronal deformity and spinal stenosis likely contribute at least as much. While prior studies have shown stronger correlations between sagittal imbalance and symptoms, these have tended to include a large number of post-fusion patients. As the authors point out, sagittal imbalance may have a more pronounced effect on the post-fusion patient than on the patient who has yet to have surgery. Major questions still remain unanswered in the sagittal balance realm. While it seems to have pronounced effects on some patients, many with poor sagittal imbalance, especially older patients, are unaffected by it. Assuming the surgeon can diagnose sagittal imbalance as a cause of symptoms, the next question is how to address it surgically. Finally, the spine community needs to decide what complication rate and costs are acceptable when performing these large magnitude, high morbidity procedures. We are all looking forward to the results of this study to determine how adult lumbar deformity patients do with surgery and non-operative treatment. There are sure to be many subgroup analyses looking at the role of sagittal imbalance, and hopefully those can provide surgeons with much needed guidance on the topic.
Please read Dr. Chapman's article on this topic in the November 15 issue. Does this change how you consider sagittal imbalance? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor
1. Glassman SD, Bridwell K, Dimar JR, Horton W, Berven S, Schwab F. The impact of positive sagittal balance in adult spinal deformity. Spine 2005;30:2024-9.
Friday, November 11, 2016
There is substantial literature linking malnutrition to post-operative complications, namely wound healing problems and infection. However, this is a relatively hard topic to study since infection and malnutrition are both relatively uncommon, and a huge number of patients are required to sufficiently power a study on the topic. In order to better assess the association between protein malnutrition and complications following lumbar fusion, Dr. Bohl and colleagues from Chicago used the National Surgery Quality Improvement Program (NSQIP) database to evaluate the relationship between hypoalbuminemia (defined as pre-operative albumin level < 3.5 g/dL) and complications. They identified over 4,000 patients who had underwent 1 to 3 level posterior lumbar fusion and had a pre-operative albumin level in the database. Surprisingly, approximately 40% of patients had a pre-operative albumin value recorded. They found that only 4.8% were hypoalbuminemic, and that elderly patients, the morbidly obese, and those with insulin-dependent diabetes, COPD and, anemia were more likely to have low albumin levels. After controlling for baseline characteristics and comorbidities, they found that hypoalbuminemia was associated with a greater risk of wound dehiscience (RR=5.8), surgical site infection (RR=2.5), urinary tract infection (RR=2.5), and 30 day readmission (RR=1.8).
This paper provides relatively strong support that hypoalbuminemia is associated with post-operative wound complications and infection. One question that arises is whether low albumin levels play a role in the causal chain leading to complications or if it is simply a marker for other medical problems that are the true cause of the wound problems and infection. The answer to this question is important because if hypoalbuminemia causes wound healing problems and infection, correcting it pre-operatively could reduce the rate of complications in malnourished patients. On the other hand, if it is simply a marker for other health problems, correcting it with pre-operative nutritional supplementation may not reduce the rate of wound problems and infections in these patients. While the authors did control for baseline characteristics and comorbidities, such statistical methods are never perfect, and unmeasured confounders always exist. Large database studies are frequently criticized for lacking the level of detail necessary to provide meaningful data for spine surgery outcomes (namely patient reported outcomes), though this study question lends itself almost perfectly to a large administrative database analysis. Both the exposure (hypoalbuminemia) and the outcome (wound complication or infection) are relatively rare, so a huge number of patients are required to answer the question. Additionally, NSQIP is very good at capturing problems like wound complications and infections, most of which occur in the 30 day post-operative surveillance window. The authors should be congratulated on using the NSQIP database appropriately to address an important question. The even more compelling question that remains is whether correcting pre-operative hypoalbuminemia would actually reduce wound complications and infections.
Please read Dr. Bohl's article in the November 1 issue. Does this motivate you to check albumin levels and try to correct hypoalbuminemia pre-operatively? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor