The Spine Blog

Friday, December 15, 2017

Pseudarthrosis is a common phenomenon after ACDF, with rates around typically cited around 10% for a one level procedure and up to 30% or more for a three level fusion. Most surgeons don’t expect a solid fusion before one year, but concern about nonunion tends to develop around the twelve month follow-up. While many patients with radiographic pseudarthrosis at one year are asymptomatic, some have persistent axial neck pain or radiculopathy without evidence of mechanical failure. The best approach to this patient is unknown, and many surgeons would consider a revision fusion procedure to address the pseudarthrosis. In order to address this void in the literature, Dr. Lee and colleagues from Korea published their series of 89 consecutive ACDF patients (51 one level, 26 two level, 12 three level) who had dynamic x-ray and CT scan evaluation at one year follow-up. They had a stringent definition of union, requiring less than 1 mm of motion between spinous processes from extension to flexion, bony union across the fusion site, and no significant radiolucent lines through the graft-bone interface. Based on this definition, they found an overall one year radiographic pseudarthrosis rate of 33% (30% for one level, 35% for two level, and 42% for three level). The radiographic studies were repeated at two years in the pseudarthrosis patients, and they found that 21 out of 29 (73%) had gone onto a solid fusion at two years without any further intervention. Three of the pseudarthrosis patients had evidence of mechanical problems on the one year imaging studies (i.e. screws backing out, bent plate), and all three went onto solid fusion by two years. Patients who had persistent pseudarthrosis at two years had worse axial neck pain and neck disability index scores compared to those with a solid fusion, though there was no difference in arm pain. In logistic regression, the only significant risk factor for pseudarthrosis was multilevel fusion.

Spine surgeons will find this paper very reassuring as the majority of patients with radiographic nonunion at 12 month follow-up went onto a solid fusion by two years without any further intervention. While it can be difficult to continue observation on patients with persistent neck pain and a pseudarthrosis at 12 months, revision fusion in these patients (either anterior or posterior) tends to have mediocre outcomes as the radiographic nonunion may not be the pain generator in all cases. The fact that even patients with evidence of mechanical failure can go onto fuse beyond one year indicates that fusion can be a slow process, and patients and surgeons need to be patient. The main limitation of this study is their very stringent definition of union. Unless a pattern recognition program was used for the intervertebral motion measurements, a threshold of 1 mm of motion to define a nonunion is likely within the measurement error for that technique. Additionally, radiolucent lines between the graft and vertebral body can persist in solid fusions when the fusion occurs around the graft rather than through it. This strict definition of union is likely the reason behind the high one year pseudarthrosis rate reported in this paper, and it seems likely that some cases that were clearly well on their way to fusion at one year were classified as nonunions. This would bias the results towards indicating a better prognosis for going onto a solid fusion by two years as many of their “nonunions” may not have been considered as such by a surgeon in the clinic. It seems as though a patient with 2 mm of motion and some bony bridging at one year has a much better chance of going onto a fusion by two years than a patient with no evidence of fusion and gross motion. Despite this limitation, this paper offers fairly good evidence to suggest there is no need to jump into a revision fusion procedure at 12 months in cases of radiographic pseudarthrosis after ACDF.

Please read Dr. Lee’s paper on this topic in the January 1 issue. Does this change how you consider treating radiographic pseudarthrosis one year after ACDF? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor

Friday, December 8, 2017

Incidental durotomy is likely the most common complication associated with lumbar decompression surgery, occurring at a rate of approximately 10% in lumbar laminectomy.1 While the vast majority of durotomies are benign and are not associated with adverse outcomes, a small minority can be associated with nerve root injury, persistent CSF leak, infection, and reoperation. Most incidental durotomies are successfully repaired during the index surgery, but a small proportion are diagnosed in a delayed fashion or result in persistent CSF leak despite repair. There is little published on medical malpractice claims related to incidental durotomy, so Durand et al. from Brown University queried three legal databases and identified 48 malpractice cases related to durotomy that either went to trial or settled. The majority  (56.3%) resulted in a verdict favoring the surgeon, with the remainder favoring the patient through a verdict or settlement. Over 80% alleged a significant neurological injury, 56% were associated with additional surgery, and 44% alleged delayed diagnosis or treatment. Factors associated with a significantly increased proportion of plaintiff verdicts included delayed diagnosis or treatment (62%), improper repair technique (73%), and male gender (58%). There was a trend towards increased likelihood of plaintiff victory as the severity of neurological injury increased (70% for paralysis or death, 41% for nerve root injury, 17% for minor injury).

This is an interesting study that provides the first quantitative analysis of malpractice claims related to incidental durotomy, the most common complication in lumbar spine surgery. It suggests that avoiding a delayed diagnosis and performing the best repair possible might help reduce the risk of a successful malpractice suit. Interestingly, returning to the OR did not significantly increase the risk of a suit, indicating that prompt diagnosis and treatment of a persistent CSF leak may mitigate the risk of legal action. The limitations of this study need to be considered, most importantly that the studies selected for inclusion represent a convenience sample and are not necessarily representative of the entire cohort of malpractice suits. No database includes all malpractice suits, so the absolute number of suits and trends in the number of suits over time are not known. Additionally, only 48 suits were included, so subgroup analyses looking at the association of certain characteristics with lawsuit outcome are likely underpowered. Finally, many suits are filed and subsequently dropped, and no data is available on these cases. Given that dropped cases are not included, it is likely that the overall rate of plaintiff victory is less than in the current series. Surgeons should find these data reassuring, as they suggest that uncomplicated dural tear that is repaired successfully rarely leads to successful litigation. Additionally, prompt recognition of a persistent CSF leak that results in reoperation also does not significantly increase the risk of a plaintiff verdict.

Please read this article that has been published ahead of print:

Does it change how you view durotomy-associated malpractice claims? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor

Friday, December 1, 2017

There has been concern about a potential link between BMP-2 and cancer ever since the FDA declined to approve a 40 mg preparation of the product due to concerns about possible carcinogenicity. Carragee et al. published multiple articles on the topic after analyzing data from FDA IDE trials suggesting a higher rate of cancer in patients exposed to BMP-2 compared to iliac crest bone graft controls, though many of the cancers included in the analysis were skin cancers. Two meta-analyses of the IDE trial data concluded that the risk of cancer was slightly increased, but the cancers were heterogeneous and no strong conclusions could be drawn.1,2 Multiple studies using large administrative databases have not found a link between BMP-2 and cancer.3-5 Given the high rate of pseudarthrosis in long thoracolumbar fusions to the pelvis in adult deformity patients, some surgeons have started to use high doses of BMP-2 to prevent this complication and have reported significantly higher fusion rates compared to iliac crest.6 In an effort to determine if high dose (at least 40 mg) BMP-2 is associated with increased cancer risk, Baldus and colleagues from Washington University retrospectively reviewed 642 patients who had received at least 40 mg of BMP-2 for a posterolateral fusion and had at least 2 years of follow-up. Their population consisted of predominantly middle aged females (average age 52.8, 77% female) who received an average of 113.5 mg of BMP-2. Eighty-five percent of patients received just one BMP-2 dose, with the remaining 15% receiving between 2 and 8 doses. Overall, 5.1% of patients developed cancer in the follow-up period, compared to a predicted rate of 5.7% based on National Cancer Institute (NCI) data. No patients developed multiple cancers. Breast cancer was diagnosed in 9/30 of the cancer patients, representing the most common diagnosis. Twelve other cancer types were reported. There was no relationship between dose or number of exposures and cancer risk. Basal cell and squamous cell carcinomas were not included as they are not part of the NCI Surveillance, epidemiology, and end result (SEER) program.

The authors have done a nice study that represents the first analysis of the association between very high dose BMP-2 and cancer. The data provides relatively convincing evidence that very high dose BMP-2 use does not increase the risk of cancer above the expected rate for an age-matched general population. The lack of a control group of similar fusion patients who did not receive BMP-2 is the study’s major limitation, as it is possible that the group of patients selected for adult deformity surgery were healthier and had a lower risk profile than that of the general population. The FDA IDE trials also demonstrated overall cancer rates below that predicted by NCI SEER data, but the BMP-2 group had a somewhat higher cancer rate than the controls. While the FDA IDE trial data is the only Level 1 data on this topic, there was a relatively low number of patients included, a high proportion of skin cancers included in the cancer diagnoses, a heterogeneous group of cancers, and borderline statistical significance. The large administrative database studies were not randomized, but they suggested no link between BMP-2 and cancer. The current study is important as it includes by far the highest average dosage of BMP-2, and it showed no increased risk versus the rate predicted by SEER data and no dose-response relationship. Putting all of this data together suggests that any association between BMP-2 and cancer is likely very weak. In challenging fusion environments (i.e. long fusions to the pelvis in adult deformity, revisions for pseudarthrosis, smokers), the potential risks associated with BMP-2 are likely justified by the benefit of a better fusion rate. However, there is little or no evidence that BMP-2 is indicated for straightforward one and two level instrumented fusions where high fusion rates can be obtained with local bone graft.

Please read this article in the December 1 issue. Does this change your perspective about the association between BMP-2 and cancer? Let us know by leaving a comment on The Spine Blog.



1.            Fu R, Selph S, McDonagh M, et al. Effectiveness and harms of recombinant human bone morphogenetic protein-2 in spine fusion: a systematic review and meta-analysis. Annals of internal medicine 2013;158:890-902.

2.            Simmonds MC, Brown JV, Heirs MK, et al. Safety and effectiveness of recombinant human bone morphogenetic protein-2 for spinal fusion: a meta-analysis of individual-participant data. Annals of internal medicine 2013;158:877-89.

3.            Dettori JR, Chapman JR, DeVine JG, McGuire RA, Norvell DC, Weiss NS. The Risk of Cancer With the Use of Recombinant Human Bone Morphogenetic Protein in Spine Fusion. Spine (Phila Pa 1976) 2016;41:1317-24.

4.            Dimar JR, 2nd, Glassman SD, Burkus JK, Pryor PW, Hardacker JW, Carreon LY. Clinical and radiographic analysis of an optimized rhBMP-2 formulation as an autograft replacement in posterolateral lumbar spine arthrodesis. The Journal of bone and joint surgery American volume 2009;91:1377-86.

5.            Kelly MP, Savage JW, Bentzen SM, Hsu WK, Ellison SA, Anderson PA. Cancer risk from bone morphogenetic protein exposure in spinal arthrodesis. J Bone Joint Surg Am 2014;96:1417-22.

6.            Kim HJ, Buchowski JM, Zebala LP, Dickson DD, Koester L, Bridwell KH. RhBMP-2 is superior to iliac crest bone graft for long fusions to the sacrum in adult spinal deformity: 4- to 14-year follow-up. Spine 2013;38:1209-15.


Friday, November 24, 2017

The increasing rate of complex lumbar spine surgery in the United States has been well-documented.1 Explanations for this trend have included technological advancement, elderly patients expecting higher levels of function, and reimbursement models that incentivize complex fusion surgery. Trends in surgery rates for spinal stenosis in other countries has not been well-studied. Given this void in the literature, Machado et al. analyzed trends in spinal stenosis surgery rates in New South Wales, Australia from 2003-2013. They analyzed an administrative database to determine the rates of decompression alone, simple fusion (one or two level posterior or anterior surgery), and complex fusion (greater than two level fusion and/or anterior-posterior surgery). They reported a 16% increase in the rate of decompression, over a two-fold increase in simple fusion, and a four-fold increase in complex fusion. After adjusting for the aging population, the overall rate of surgery increased by 13%. Not surprisingly, length of stay, hospital cost, and complication rate increased with increasing surgical complexity. The authors expressed concern that there was in increasing rate of complex surgery without evidence supporting its use.

The authors have made an interesting addition to the literature by investigating surgical trends outside of the United States. Similar to the United States, Australia pays physicians on a fee for service basis, so surgeons are financially incentivized to perform complex surgery. It would be interesting to see a similar analysis from a country that does not pay surgeons on a fee for service basis. The limitations of this study need to be understood before drawing any strong conclusions. This administrative database did not include diagnoses more specific than spinal stenosis, so it is unknown how many patients had surgery for spondylolisthesis or scoliosis, diagnoses for which fusion is generally indicated. The complication rates were very low, so it is likely that many important complications were not captured in the billing data. Patient reported outcomes were not available in this database, so it is unclear if or how the different surgical techniques affected outcomes. It seems likely that the rate of complex fusion is increasing across the modernized world. There are likely many reasons for this related to improved surgical and anesthetic techniques, changing patient expectations, better understanding of sagittal balance, and financial incentives for surgeons. There are clearly patients who benefit from complex lumbar fusion and others who do well with a simple decompression. However, many patients have pathology for which we do not have evidence-based guidance regarding the best treatment. Surgical decision-making in this gray zone may be affected by surgeon bias or financial incentive to a greater degree than the clear-cut cases. The “right” rate of surgery and different surgical techniques remains unknown. Until research allows for better prediction of outcomes based on individual patient characteristics, surgical decision-making will remain more art than science and be prone to bias by non-medical factors.

Please read this article in the November 15 issue. What do you think about trends towards increasingly complex surgery for spinal stenosis? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor


1.            Deyo RA, Mirza SK, Martin BI, Kreuter W, Goodman DC, Jarvik JG. Trends, major medical complications, and charges associated with surgery for lumbar spinal stenosis in older adults. Jama 2010;303:1259-65.


Saturday, November 18, 2017

Proximal junctional kyphosis (PJK) is a common failure mode following adult deformity surgery. There has been debate about risk factors for developing PJK, with authors having suggested overcorrection, undercorrection, upper instrumented vertebra (UIV) in the lower thoracic spine, and osteoporosis as potential risk factors. In order to better understand factors contributing to PJK, Dr. Nicholls and colleagues reviewed 9 years of adult deformity cases (n=440) performed at UCSF and developed a multivariate model to determine predictors of PJK and of revision surgery for PJK. PJK was defined as a proximal junctional angle (PJA) of at least 10 degrees that had increased by at least 10 degrees from the initial post-operative x-ray. They found that 36% had developed PJK at a mean follow-up of nearly 3 years. Of those with PJK, 41% underwent revision surgery to address it (15% overall revision rate for PJK). In the univariate analysis, patients who developed PJK were significantly older, more likely to be female, had longer follow-up, had greater pre-operative and post-operative thoracic kyphosis (TK), greater pre-operative pelvic tilt (PT), and were less likely to have a hook at the UIV. Multivariate logistic regression demonstrated that pre- and post-operative TK, post-operative PT, and UIV pedicle screw instrumentation were all significant independent predictors of PJK. Lower age, increased post-operative sagittal vertical axis (SVA), increased post-operative PJA, and listhesis at the proximal level were all significantly associated with revision surgery for PJK.

The authors have compiled a large sample of adult deformity patients in an effort to identify risk factors for PJK, a significant complication that commonly leads to revision surgery. Among the risk factors identified for PJK, higher pre- and post-operative TK and high pre-operative PT predicted PJK, while a hook at the UIV was protective against PJK. The authors theorized that patients who had a high pre-operative TK and PT likely had stiffer spines that failed to adapt to increasing sagittal imbalance by flattening the physiological TK. These findings are consistent with some of the recent literature on this topic that demonstrated that patients with more severe baseline pathology who undergo greater correction are more likely to develop PJK.1 While modern approaches to sagittal imbalance depend on lordosis increasing osteotomies, they do not address the soft-tissue structures ventral to the spine that have contracted and apply kyphosing forces following realignment procedures. Additionally, central mechanisms may lead older patients to assume a more kyphotic posture, and there seems to be a natural tendency for older patients to adopt their baseline posture despite realigning the caudal portion of the spine. This paper does not seem to have analyzed some of the factors that have been proposed as risk factors for PJK, including osteoporosis and UIV level. It is not clear if magnitude of correction was considered as a risk factor. This paper suggests that patients with stiffer, more severe deformity—as indicated by increased TK and PT—are at higher risk for PJK. It seems likely that less aggressive correction may decrease the failure rate in these patients, though this needs to be balanced against the desire to correct patients enough to provide relief from their sagittal imbalance.

Please read Dr. Nicholls'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  



1.            Lafage R, Schwab F, Glassman S, et al. Age-Adjusted Alignment Goals Have the Potential to Reduce PJK. Spine (Phila Pa 1976) 2017;42:1275-82.