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The Spine Blog

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

Sunday, April 14, 2019

Risk factors for readmission after spine surgery have been studied extensively, generally using large administrative databases. Smaller investigations looking at the experience at a single institution have also been published but have generally included fewer patients and have been relatively underpowered. While administrative databases include large numbers of patients, they generally lack the clinical details germane to spine surgery necessary to draw meaningful conclusions. The Quality and Outcomes Database (QOD) was created to capture large numbers of spine surgery patients along with the important details relevant to spine surgery such as patient reported outcomes, underlying diagnosis, and surgical technique. This database captures spine surgery patients from 86 institutions in the United States through chart review and patient questionnaires. The current study used data from over 33,000 lumbar surgery patients in order to evaluate risk factors for 90-day readmissions. Patients with deformity, infection, trauma, and tumor were excluded. The authors classified the readmissions as medical (i.e. DVT, PE, cardiac disease, renal disease, non-surgical site infection, etc.) or surgical (i.e. surgical site infection, wound dehiscence, CSF leak, disk reherniation, hardware failure, new neurologic deficit, hematoma or pain) and developed multivariate regression models evaluating risk factors for the two types of readmissions. The overall 90-day readmission rate was 6.15%, with 2.5% being readmitted for medical complications and 3.6% for surgical complications. The risk factors for both medical and surgical readmission were higher ASA grade, increased number of levels treated, higher baseline ODI score, and anterior approach. Increased age, male gender, heart disease, unemployment, fusion, and not smoking were risk factors specific for medical readmission. Specific surgical readmission risk factors included increased BMI, female gender, depression, and African American race. With the possible exception of non-smokers being at higher risk for medical readmission, these risk factors are consistent with the prior literature on the topic.

The authors have done a nice job using a relatively novel dataset to explore risk factors for readmission following lumbar surgery. They identified the usual suspects for readmission—increasing age, medical and psychosocial comorbidities, and surgical invasiveness. The one anomaly is that smokers were at somewhat lower risk for medical readmission, though this has been shown in prior studies. The causal chain behind this association is not clear, though active smokers may be generally younger and more robust than non-smokers. Additionally, smokers are strongly motivated to stay out of the hospital where smoking is not permitted, and they have shorter hospital length of stay following surgery. While this study does not provide any new information, it supports what has been shown in the literature and this consistency helps to validate the QOD database. The real question is whether this information can be used to identify patients at high risk for readmission and intervene in some way to lower their readmission rate. Very little has been published on this, though it seems that diverting increased resources (i.e. nurse phone calls, visiting nurses, more frequent follow-up with primary care providers, etc.) to high-risk patients could save resources in the long-run. While some complications and readmissions are unavoidable, many readmissions could likely be avoided with increased intensity of post-operative care. Currently, decisions about which patients to target for more post-operative surveillance are based on provider perception and patient demand. Models like those in the current study might be used to select patients for such an intervention in a more accurate, objective fashion. Hopefully future studies will evaluate such programs to determine if they are effective.

Please read the article by Dr. Sivaganesan and colleagues in the April 15 issue. Does identifying these risk factors change how you will target patients for increased post-operative surveillance? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor

Friday, April 5, 2019

Spinal epidural abscesses (SEA) are occurring more frequently in our older, sicker population as well as in the increasing intravenous drug user population. These serious infections are difficult to treat and can result in neurological deficit, sepsis, and death. Treatment traditionally involved surgery and IV antibiotics for all epidural abscess patients, though recent literature suggests that medically stable patients without a neurological deficit can frequently be treated successfully with antibiotics alone. While the incidence of SEA is increasing, the absolute number of cases, particularly the number treated at a single institution, remains relatively low and makes powering studies on the topic difficult. In order to obtain a sufficient sample size to study the topic, Dr. Du and colleagues from Cleveland analyzed the NSQIP database and identified 1094 patients who underwent surgical treatment of SEA from 2011 to 2016. The NSQIP database includes outcomes and events up to 30 days following surgery, which allowed them to calculate a 30 day mortality rate of 3.7%. Risk factors for mortality included increased age, higher ASA class (indicating a greater comorbidity burden), diabetes, hypertension, respiratory disease, renal disease, bleeding disorder, metastatic cancer, thrombocytopenia, and receiving a perioperative blood transfusion. Multivariate analysis demonstrated that age over 60 years, diabetes, respiratory disease, renal disease, metastatic cancer, and thrombocytopenia were independent risk factors for mortality. Having 4 or more of these risk factors was associated with a 38% mortality compared to less than 1% mortality for patients with no risk factors. Seventy percent of deaths occurred within 2 weeks of surgery, though 10% occurred between 27 and 30 days post-operatively. Not surprisingly, cardiac arrest and septic shock were strongly associated with death.  

The authors have done a nice job using a database to study a topic that is very difficult to study using traditional chart review given the relatively low number of patients who undergo surgery for SEA at any single institution. Additionally, death is a good outcome to study using a large database as it is captured reliably. Nonetheless, the study has all of the limitations associated with a database study, notably that many relevant variables such as neurological status, intravenous drug use, and cause of death were not included. Additionally, the database does not record death beyond 30 days from surgery, yet the data makes it clear that patients were continuing to die at a significant rate even at 30 days out from surgery. The paper provides a good benchmark mortality rate following surgery for SEA. While it did identify risk factors for mortality, none of these come as a surprise, and all are indicative of systemic disease burden which increases mortality risk for all types of surgery. Surgeons need to decide which SEA patients should undergo surgery, and this paper does not help answer that question. While sicker SEA patients are at higher risk for mortality, it is unclear how surgery affects this risk. Some patients may have a survival advantage with surgery due to a higher chance of clearing their infection, while other patients may succeed with antibiotic treatment alone and have an increased risk of mortality due to the physiological stress of surgery. Most patients survive regardless of treatment, and a small minority are so sick that they will likely die however they are treated. To answer this question would require a huge database of patients treated with surgery and medical management that also includes a sufficient number of clinical variables that could be used to create an accurate predictive model. An RCT to address this question is not feasible. It is possible that a Medicare database analysis could provide some further insight, but this administrative database includes only billing data and likely misses some of the key clinical variables. For now, surgeons will probably continue to operate on most SEA patients with neurological deficit, sepsis, or failed medical management.

Please read Dr. Du's article in the April 15 issue. Does this change how you view the treatment of SEA? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor

Friday, March 29, 2019

Concern about iliac crest bone graft (ICBG) harvest site morbidity has helped create a massive bone graft substitute industry and prompted many spine surgeons to use local bone graft and bone graft substitutes instead of ICBG, despite ICBG resulting in better fusion rates. The major concern relates to ICBG harvest site pain, though increased blood loss, operating time, hematoma formation, infection, and the potential for injury to surrounding structures are other reasons cited to avoid ICBG. While ICBG harvest site morbidity has traditionally been accepted as fact, more recent research suggests that long-term pain or other major complications are in fact quite rare when harvest is performed through the same midline incision used for lumbar fusion. In order to better assess ICBG harvest site pain, Lehr and colleagues from The Netherlands performed a prospective, patient-blinded study in which ICBG was randomly harvested from either the right or left iliac crest and patients were asked to identify from which side the graft was taken and to rate their midline back pain and bilateral iliac crest pain at baseline and then at four follow-up visits out to one year. This study was performed as part of a larger investigation comparing calcium bone graft substitute to ICBG. Ninety-two patients underwent instrumented lumbar fusion for degenerative conditions, with the fusion extending to the lower lumbar spine (L3 or more caudal). The majority (87%) underwent one or two level fusion. All patients had ICBG harvested and placed in one lateral gutter, with the calcium bone graft substitute placed on the contralateral side. The ICBG was harvested by creating a unicortical iliac crest window and removing the cancellous bone with gauges. Median harvested bone graft volume was 6 cc. Following surgery, 49% of patients reported that they did not know from which side the ICBG was harvested or answered inconsistently across the four follow-up visits. Of the 51% who felt they could identify which crest was harvested and answered consistently at all follow-up visits, 48% identified the correct harvest site and 52% identified the wrong crest. Overall, 24% of patients consistently and correctly identified the ICBG site over the first year following surgery. There were no significant differences in median iliac crest pain scores between the harvested and intact iliac crests at any follow-up point, and iliac crest pain scores correlated with midline low back pain scores. Based on this, the authors concluded that ICBG harvest did not result in increased pain at the harvest site, and that concern about harvest site pain should not be the main reason to avoid ICBG harvest.

The authors have done an elegant study and compelling analysis, which strongly suggests that most patients do not experience prolonged ICBG harvest site pain. The study design was appropriate, though it does have a few significant limitations. The amount of bone graft harvested seems very low (median of 6 cc), and most surgeons traditionally harvest more than this. A more extensive bone graft harvest could result in higher levels of graft site pain. The authors did not report any complications related to bone graft harvest or discuss any increase in blood loss associated with the procedure. While rare, complications related to graft site harvest do occur (i.e. hematoma, infection, injury to structures in the sciatic notch), and any additional surgical work increases blood loss. They also note that median bone graft harvest only took 7.5 minutes, which might be related to the low volume of graft obtained. A more thorough harvesting technique, irrigation, control of bleeding bone, and closure typically takes longer than that. Despite these limitations, the current study and recent literature suggests that pain and morbidity associated with ICBG harvest is much lower than suggested by the historical literature on the topic. The earlier studies frequently included harvest through a separate incision and removal of the entire outer cortex of iliac crest. At this point, surgeons may be avoiding ICBG harvest more out of an effort to reduce time in the operating room than out of concern for harvest site morbidity. However, this study and others suggest that ICBG should be strongly considered as a graft option given its better osteoinductive properties and low morbidity associated with its harvest.

Please read the article on this topic in the April 15 issue. Does this change your view about the morbidity of ICBG harvest? Let us know by leaving a comment on The Spine Blog.

Adam Pearson MD, MS

Associate Web Editor

Friday, March 22, 2019

The urgency of lumbar discectomy for patients with significant motor weakness has been debated, with most studies on the topic demonstrating minimal benefit for more urgent decompression. However, there is some evidence that decompression in under 48 hours following the onset of cauda equina syndrome leads to better functional outcomes. No study has looked at the role of immediate surgery for lumbar disc herniation associated with motor weakness, likely because few discectomies are performed in under 48 hours of the onset of weakness. In order to assess the effect of immediate discectomy on motor outcomes, Dr. Petr and colleagues from Innsbruck retrospectively reviewed a series of 330 lumbar disc herniation patients who presented with motor deficit. They divided the patients into two cohorts depending on whether they underwent surgery within 48 hours of the onset of weakness or beyond 48 hours. The immediate surgery group included 126 patients, while the delayed surgery group included 204. There were no significant demographic or baseline clinical differences between the two cohorts. Approximately 60% of the herniations were at L4-L5 and about 20% were at L5-S1. Twenty-four percent of patients had mild (grade 4/5) weakness, 53% had moderate (grade 3/5) weakness, and 23% had severe (grade 0-2/5) weakness. Postoperatively, the immediate surgery group had a greater improvement in motor strength at discharge, 6 weeks, and 12 weeks follow-up.  The difference was not significant for the mild weakness group, in which 96% of the immediate surgery group had complete resolution of motor weakness at 12 weeks compared to 86% in the delayed surgery group (p=0.22). The differences were significant in the moderate and severe weakness groups, with 96% of the severe weakness group undergoing immediate surgery having complete resolution at 3 months compared to 64% of the delayed surgery group. The immediate surgery group also had greater resolution of sensory deficits. There were no differences in the rate of residual sciatica between the immediate and delayed surgery groups.

The authors have presented a thorough retrospective analysis of their lumbar discectomy cohort that suggests that discectomy patients with a preoperative motor deficit have greater recovery of motor function if their surgery is performed within 48 hours of the onset of the deficit. While this intuitively makes sense, prior studies have not consistently demonstrated this. One reason for this discrepancy is that prior studies tended not to look at the effect of immediate surgery within 48 hours of symptom onset as surgery is rarely performed this quickly for logistical reasons. It is impressive that the authors were able to perform surgery within 48 hours on over 1/3 of their lumbar discectomy patients with motor deficits. The authors point out that this is not an RCT, so no strong conclusions regarding causation can be drawn. One limitation is that they did not report the duration of symptoms for patients undergoing surgery beyond 48 hours after the onset of symptoms. It is possible that some of these patients had long-term motor deficits (i.e. months or more), and these were probably less likely to improve. Many patients present with an acute motor deficit that resolves relatively quickly without surgery, so it is not clear to what degree immediate surgery changed the natural history of the motor deficit. Given that the timing of surgery was not randomized, the two groups were likely different at baseline in ways not measured by the study. A future study RCT comparing immediate surgery to delayed surgery and no surgery would answer the question, though it is not clear that such a study would ever be performed due to ethical concerns and strong patient preferences. I see very few patients in my practice who present with a motor deficit that has been present for less than 48 hours, primarily due to logistical issues around referrals and imaging. For that reason, I am not sure that immediate surgery is even logistically feasible for most healthcare systems.

Please read Dr. Petr's article on this topic in the April 1 issue. Does this change your view on immediate surgery for lumbar disc herniation with motor deficit? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor