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The Spine Blog

Saturday, December 8, 2018

If spine patients and their surgeons could see the future, surgical decision-making would be very easy. The patient would know how they would do with surgical or non-operative care and then choose the option that leads to their preferred result. Unfortunately, the science of predicting spine patient outcomes based on individual characteristics is in its infancy. In an effort to individualize outcome predictions for patients with disk herniation, spinal stenosis, and degenerative spondylolisthesis, Haley Moulton and colleagues from Dartmouth-Hitchcock, Washington University, and OrthoCarolina worked with Consumer Reports using data from the Spine Patient Outcomes Research Trial (SPORT) to develop outcomes prediction models for surgical and non-operative treatment for each diagnosis. The outcomes included were the SF-36 physical function score, sciatica or stenosis bothersomeness index, sleep quality, and sex life. Consumer Reports worked with investigators to create a user-friendly website for patients that provided information about their condition and an individualized prediction of surgical and non-operative outcomes out to 8 years based on their characteristics. Two groups of respondents were queried:  over 1,200 Consumer Reports subscribers known to have low back pain and 68 patients identified from spine center clinics. The Consumer Reports patients tended to be older and included a higher proportion of men with longer term, less severe symptoms as compared to those recruited from clinic. The Consumer Reports respondents were also not screened by a spine clinic provider, so they determined their own diagnostic category. The study participants were randomly assigned to take a knowledge quiz before or after using the website, and the group who took the quiz after using the website scored higher. Decisional conflict tended to be lower after using the website, though this was more pronounced for the Consumer Reports respondents. Overall, the participants found the calculator at least moderately useful, and the majority were very or completely satisfied with its ease of use.

To many spine providers, having an accurate way to predict surgical and non-operative outcomes for individual patients is the holy grail of surgical decision-making. It would allow for the selection of surgical patients who would have a high chance of surgical success and the avoidance of surgery in patients who would do just as well with non-operative treatment or be at high risk for a bad complication. A perfectly accurate prediction model will never exist, but an outcomes calculator like the one described here should help patients and surgeons make a more informed decision. This paper would have been stronger if more patients who were actual surgical candidates were enrolled. Only about 20% of patients identified in clinic and provided with a link to the website actually used it, suggesting that most patients were not particularly interested in using the program. It is possible that handing them a card with a web address they needed to type into their computer or phone was not the best way to recruit them into the study. It is harder to interpret the data from the Consumer Reports respondents as they self-identified as having one of the three conditions under study, and many of them were probably not surgical candidates (their patient reported outcome scores indicated much less severe symptoms compared to the clinic patients). It seems likely that prediction models will appeal to at least a substantial minority of relatively sophisticated patients who have an interest in this type of data. Other patients may prefer a simple treatment recommendation from their provider. In an ideal world, patient outcomes would be recorded in a registry, and the model's accuracy could be improved as more patients are followed. Individualized outcomes prediction represents a major addition to shared decision, and hopefully this information will help patients and surgeons come to the right treatment decision.

Please read Ms. Moulton's article on this topic. Do you think such a calculator would be helpful to you and your patients? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Wed Editor


Friday, November 30, 2018

Cervical spondylotic myelopathy (CSM) is a relatively common cause of balance dysfunction and loss of manual dexterity in the middle aged and elderly population. Like many spinal conditions, there is not a gold-standard test available to make the diagnosis. The combination of symptoms (i.e. clumsy hands, off balance), physical exam findings (hyperreflexia, Hoffman's sign, clonus, etc.), and MRI demonstrating cord compression are necessary to make the diagnosis. For patients with severe CSM, the diagnosis is frequently straightforward, though mild or atypical cases can be much harder to diagnose. Given the lack of a gold-standard test, providers would benefit from a better understanding of the test characteristics of factors that go into the diagnosis. To quantify the test characteristics of the physical exam maneuvers that contribute to the diagnosing CSM, Dr. Fogarty and colleagues performed a literature review and meta-analysis on the topic. The only physical exam test with any even moderate quality data regarding test characteristics was the Hoffman sign, so their paper focused on this test. They found three papers including patients referred to a spine surgeon for cervical complaints that reported the sensitivity and specificity of the Hoffman sign, using MRI as the "gold standard" diagnostic tool. The authors combined the 3 studies to yield 201 patients, 46% of whom had an MRI "diagnosis" of myelopathy. Overall, the Hoffman sign had a sensitivity of 59% and specificity of 78%, corresponding to a false negative rate of 41% and a false positive rate of 22%. The positive likelihood ratio (proportion of CSM patients with a positive Hoffman sign divided by non-CSM patients with a positive Hoffman sign) was 2.6 and the negative likelihood ratio (proportion of CSM patients with a negative Hoffman sign divided by non-CSM patients with a negative Hoffman sign) was 0.5. Based on these findings, they concluded that a positive Hoffman sign slightly increased the likelihood of having CSM, while a negative Hoffman sign did not significantly alter the pre-test probability.

The authors have done a nice job synthesizing and quantifying the limited available data on this topic. Spine providers are clinically aware of the relatively low sensitivity and specificity of the Hoffman sign and most other physical exam findings that contribute to the diagnosis of CSM.  We have all seen many CSM patients without a Hoffman sign and plenty of non-myelopathic patients who have a positive Hoffman sign. One of the major limitations of any study on this topic is the lack of a gold-standard to diagnose CSM. While the papers used varying MRI findings as the "gold-standard", this is problematic as many patients can have spinal cord compression and even signal change in the cord without having clinically relevant myelopathy. This may be why there was a 46% prevalence of CSM, which seems very high for a typical spine surgery practice. The authors reported a false negative rate of 41%, which may be artificially elevated given a radiographic diagnosis of CSM (i.e. patients with cord compression without clinically evident myelopathy would not have a positive Hoffman sign yet would be characterized as a false negative). This article helps to hammer home the point that CSM is a clinical diagnosis based on the provider's gestalt after considering findings from the history, physical exam, and imaging. The authors mention doing a prospective study of patients presenting with neck pain who undergo a physical exam and MRI, but such a study would be difficult to carry out. For one, the lack of a gold-standard diagnostic test precludes accurate calculation of test characteristics. Future studies probably need to rely on an expert's clinical impression as the diagnostic gold-standard. Additionally, it would be very difficult to obtain insurance approval for an MRI in a patient presenting only with axial neck pain. A useful exercise in the future may be to create a diagnostic prediction algorithm that includes findings from the history, physical exam, and imaging findings. It is unlikely that such an algorithm would outperform an experienced expert, but it might be of use for generalists or less experienced spine providers.

Please read Dr. Fogarty's article on this topic in the December 1 issue. Does this change how you view the role of the Hoffman sign in the diagnosis of CSM? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor


Sunday, November 18, 2018

Long-term outcome data following spine surgery are hard to come by, and long-term non-operative outcomes are virtually non-existent. The Spine Patient Outcomes Research Trial (SPORT) received NIH funding for eight years of follow-up for degenerative spondylolisthesis (DS) patients treated with surgery or non-operative treatment. Over 600 patients enrolled, and approximately half agreed to be randomized to surgery or non-operative care. Twenty-eight percent of patients randomized to surgery did not undergo surgery, while 54% of those randomized to non-operative care did have surgery. This high level of treatment non-adherence prevented meaningful analysis of the RCT on an intent-to-treat basis. As such, the randomized and observational cohorts were combined in an as-treated analysis that was statistically controlled for potential confounders. The follow-up rate at 8 years was 56%, and this loss to follow-up had some potential to bias the results. In the as-treated analysis, surgery had a significant advantage compared to non-operative treatment, and this difference remained significant out to eight years. The surgery patients improved approximately 10 points more on the Oswestry Disability Index at 8 years. Similar differences were observed on the SF-36 and other outcome measures. In a subgroup analysis, there were effectively no significant outcome differences among those treated with an uninstrumented fusion, pedicle screw instrumentation, and pedicle screws plus an interbody device. At eight years, the reoperation rate was 22% and did not differ significantly across fusion techniques.

The SPORT produced some of the highest quality data available to the spine community. Despite this, significant limitations such as crossover and loss to follow-up have potentially biased the results. Nonetheless, the data are consistent across eight years of study and seem to match clinical experience. There has been significant controversy about the best surgical technique to treat DS, with ongoing debate about the most effective type of fusion1 as well as about whether fusion is even necessary.2,3 The results of the current study do not offer much new information on the topic and are limited by the fact that patients were not randomized to different fusion technique. As a result, the patients were significantly different at baseline, and, despite controlling for these differences, it is hard to know if confounders affected the outcome. A prior observational study suggested the results of uninstrumented fusion could degrade over time due to a high rate of pseudarthrosis, though this was not observed in SPORT.4 Fusion technique did not affect reoperation rate either. While the different techniques have specific advantages and disadvantages, these do not seem to affect long-term patient reported outcomes or reoperation rate. Similar to the long-term SPORT studies on spinal stenosis and disk herniation, the current study demonstrated the long-term advantage of surgery compared to non-operative treatment for DS. The best operation for DS remains unknown, and it likely depends on patient and disease characteristics. Now that most would agree that surgery leads to better long-term outcomes than non-operative treatment, hopefully future studies can help surgeons select the best surgical technique for individual patients.

Please read Dr. Abdu's article on this topic in the December 1 issue. Does this article change how you consider long-term outcomes for DS patients? Let us know by leaving a comment on The Spine Blog.

 

Adam Pearson, MD, MS
Associate Web Editor

REFERENCES

1.            Baker JF, Errico TJ, Kim Y, Razi A. Degenerative spondylolisthesis: contemporary review of the role of interbody fusion. Eur J Orthop Surg Traumatol 2017;27:169-80.

2.            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.

3.            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.

4.            Kornblum MB, Fischgrund JS, Herkowitz HN, Abraham DA, Berkower DL, Ditkoff JS. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective long-term study comparing fusion and pseudarthrosis. Spine 2004;29:726-33; discussion 33-4.

 

 


Friday, November 9, 2018

Spine surgery is technically challenging, and errors can result in complications that adversely affect patients both in the short and long term. As such, it is a difficult to teach surgical trainees safely. In the traditional apprenticeship model, trainees gradually perform an increasing number of steps in the procedure under the supervision of the attending surgeon until they are proficient and can perform the operation independently. This advancement of responsibility balances the goals of improving trainee competence and of avoiding complications due to trainee error. If these competing goals are not well-balanced, residents and fellows may not be proficient by the end of their training or patients may experience unnecessary harm. Surgical simulation offers the promise of providing risk free training for surgical residents and fellows, and it has been demonstrated to improve skills, particularly in endoscopic surgery (i.e. laparascopic cholecystectomy, knee arthroscopy). The development of high fidelity open surgical simulators has been difficult. Options include using synthetic models, animals, cadavers, and virtual reality. Unfortunately, all of these tend to be expensive and frequently lack sufficient fidelity to allow for skill transfer to real surgery. Until now, there has been scant literature describing spine surgery simulation. Drs. Coelho and Defino, from Brasil, attempted to fill this void with their article in the November 15 issue. Their study describes both a synthetic, manufactured model and a virtual reality simulator. Following development of these simulators, they asked 16 experienced spinal surgeons to evaluate them. The synthetic model was designed to represent the lumbar spine and included a soft tissue envelope, discoligamentous spine model, and thecal sac including nerve roots and saline representing CSF. This allowed for simulation of spinal exposure, pedicle screw placement, laminectomy, and durotomy repair. The virtual reality simulator was not described in great detail, but it reportedly simulated similar steps. The paper contains limited data, but they did report that 11 of 16 surgeons felt that the synthetic simulator had the potential to have a practical application in training. Even less data were reported about the virtual simulator, though all but one surgeon who tested it felt like it might have some role in spine surgery training.

The authors should be congratulated for creating spine surgery simulators, and a high fidelity simulator that allows trainees to progress along the early portion of the learning curve in a safe environment is very much needed. This paper basically served to describe their models and indicated that experienced surgeons felt they had a potential role in surgical training. A scientific paper is not the best medium to convey the details about a surgical simulator, and video or live demonstration of the simulators would be necessary to completely grasp how they function. It would be helpful to know the cost of the two simulators and the reusability of the synthetic simulator, but the authors did not report this. I imagine that the next step will be a description of how trainees perform on the simulators and then a study looking at whether using the simulators results in measurable performance improvement in the OR. I have found that using Sawbones models to train residents to place spinal hardware helps them understand the steps and gain familiarity with the instrumentation, though the model lacks fidelity and only allows progress along the very early portion of the learning curve. Virtual reality holds the promise of realistic simulated experiences including haptic feedback, though the technology does not currently exist to provide high fidelity simulation of open surgical procedures.

Please read Dr. Coelho's article in the November 15 issue. Does this change how you view the role of surgical simulation in spine surgery training? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor


Friday, November 2, 2018

S2 alar-iliac (S2AI) screws likely represent the best option for spinopelvic fixation, though their placement can be technically difficult. There is a lack of good anatomic and fluoroscopic landmarks to guide their placement, and determining if the screw is entirely within bone using fluoroscopy can be difficult. Navigation and robotic drill guide placement are newer techniques that hold promise to improve the accuracy of screw placement in spine surgery. In order to determine if a robot improves the accuracy of S2AI screw placement, investigators at Columbia University compared S2AI screw accuracy between 59 screws placed using a free hand (i.e. no image guidance) and 46 screws placed using a robot-positioned drill guide. They found an 8.5% breach rate using the free hand technique and a 4.3% breach rate using the robot, though this difference was not statistically significant. Moderate-severe breaches (>3 mm) occurred in 5.1% of free hand screws and 2.2% of robot-directed screws. They also compared the trajectory of the screws and found that the robot-directed screws aimed somewhat more caudally. No screws caused neurovascular or visceral injury, and there were no inferior breaches into the sciatic notch. Based on these data, the authors concluded that the free hand and robot-directed technique had comparable results.

The authors have done a nice job creating a comparative study looking at these two S2AI techniques. While the authors work at a busy spinal deformity center, they included only 51 patients who underwent surgery over two years. This indicates that it is very difficult to put together a large series of these cases as even busy deformity centers are not putting in large numbers of S2AI screws. The relatively low numbers involved and relatively low breach rate resulted in an underpowered study. The free hand technique had twice the breach rate as compared to the robot-directed technique, yet this difference was not close to statistically significant. Based on a lack of statistical significance, the authors concluded that accuracy was similar for both techniques, yet the data indicate that the robot might cut the breach rate in half. The only way to prove that would be to do a large, likely multicenter trial, which is always challenging and expensive. The data suggest that one of the robot-directed screws was markedly off target, likely by a centimeter or more. It would be interesting to know the mechanism of failure for that screw given that the others seemed to be placed quite accurately. Stereotactic navigation is another option for placing S2AI screws, and the authors did not comment on that. In my experience, it can be difficult for the cameras to capture the stereotactic array on the pedicle finder due to the caudal angulation required to place the screw. With all of the new technology related to placing screws more accurately, it seems as though the placement of S2AI screws can be made easier and more accurate by using the technology. It remains to be seen what technique (free hand, fluoroscopy guided, navigation, 3D printed drill guides, robots, etc.) will lead to the most accurate placement while maintaining efficient workflow. It seems unlikely that most spine surgeons will ever be able to match Dr. Lenke's skill with free hand screw placement, and even he had a 5% moderate-severe breach rate. Navigation and robotics seem to be here to stay, and it will be up to the spine surgery community to figure out how to best use these tools.

Please read Dr. Shillingford's article on this topic in the November 1 issue. Does this change how you view the role of robotics in S2AI screw placement? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor