The Spine Blog

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  

 

REFERENCE

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.

 


Sunday, November 12, 2017

Medicare reimbursement rates can drive provider and health system behavior, and private insurers use them to determine their reimbursement rates. These rates are supposed to be driven by the local costs of providing care, though the actual process by which these rates are determined is somewhat opaque. To better understand the geographic variation in and drivers of Medicare reimbursement for thoracolumbar fusion, the authors used data from the 2011 Medicare database, the US Census, and the Dartmouth Atlas to look at factors associated with DRG 460, “spinal fusion except cervical without major complications or comorbidities”. They determined average reimbursement for that DRG at the national, hospital referral region, and hospital service area level. They also created a multivariate model to evaluate drivers of reimbursement in the domains of supply, demand, competition, quality, and patient and hospital factors. Given that these are difficult factors to measure, they tended to rely on indirect measures (i.e. hospital volume of fusions as a surrogate for quality). Similar to many healthcare variables, they found relatively large geographic variation in Medicare reimbursement for fusion (mean $28,000, standard deviation $7,000), with average reimbursement for fusion varying over two-fold across hospitals. Hospitals in the South and West tended to have the highest reimbursements, while those in the Northeast had the lowest. Their multivariate model predicted 38% of the variation, so the model did not account for most of the variation. The strongest predictors of higher reimbursement were hospital charges, total Medicare reimbursement for the hospital, and number of spine surgeries per 1,000 Medicare enrollees. Orthopaedic and neurosurgeon supply were not related to reimbursement, though increasing number of hospital beds was associated with lower reimbursement. Demand, as measured by percentage of patients in the region with a diagnosis of osteoarthritis, was inversely related with reimbursement. Hospitals that were for-profit or physician-owned received lower reimbursement than non-profit or government hospitals. Quality, as measured by hospital volume and patient satisfaction scores, was inversely related with reimbursement.

This is a complex paper based on big data that is somewhat challenging to interpret. The relatively large geographic variation in Medicare reimbursement is not surprising, and the authors were unable to explain most of it with their analysis. While CMS theoretically bases reimbursements based on the cost of providing care in a region, the authors did not include these factors in their analysis. They found mixed results when considering traditional economic rules of supply and demand, with these rules holding for some factors and not for others. The authors used many indirect measures of the factors in their model, and this may have limited the precision of the measurements. The effect of patient comorbidities was effectively ignored by looking at the hierarchical condition category score at the hospital referral region level rather than looking at the fusion patients’ scores. This type of big data analysis yields many associations, most of which are statistically significant due to the large number of data points included. However, it does not provide insight into causation, and the risk for confounding by unmeasured variables is high. While there was a relationship between charges and reimbursement, it is unclear if higher charges led to higher reimbursement or vice versa. Like most papers looking at geographic variation in healthcare, this paper raises more questions than it answers. Investigators have struggled to explain geographic variation in the treatment of many conditions. In this case, the variation is determined by CMS. As such, increased transparency about how reimbursement is determined would help to explain the variation and help healthcare organizations plan for the future. As reimbursement models get more complex and driven by quality metrics, leaders of healthcare organizations need to better understand how they are getting paid.

Please read Dr. Khanna’s article in the November 1 issue. Does this change your view of Medicare reimbursement for spinal fusion? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS
Associate Web Editor


Friday, November 3, 2017

Many factors are associated with the development of degenerative spondylolisthesis (DS), most notably age and female gender. Facet orientation, pelvic alignment, and hormonal factors are also associated with DS, though the role of these specific factors is poorly defined. In order to better understand risk factors for the development of DS, Dr. Cholewicki and colleagues performed a case-control study comparing risk factors between 149 women with DS and 173 controls. Patients were between age 40 and 80, and all had either an upright lateral radiograph or an MRI to assess for DS. The DS group was almost 4 years older, had significantly higher body mass index, and more severe back symptoms based on the Oswestry Disability Index and Health Assessment Questionnaire. Addtionally, the DS group had more full term pregnancies on average (2.1 vs. 1.7), a higher rate of hysterectomies (42% vs. 23%) and other abdominal surgery (54% vs. 42%), and longer duration since menopause (18 vs. 12 years). The authors performed a multivariate regression analysis that demonstrated a 22% increase in the odds of developing DS for each pregnancy, a nearly two-fold increase with hysterectomy, and a significantly increased risk with age and increasing BMI. The other variables failed to reach significance in this model. Based on these findings, the authors hypothesized that pregnancy and hysterectomy could result in impaired functioning of the pelvic floor musculature that could lead to decreased stability of the spinal column and the development of DS.

This is an interesting study that looks at some of the questions around the etiology of DS that have been considered for decades but never completely understood. Given that female gender is the strongest predictor of developing DS other than age, hormonal factors or structural factors that differ between the genders almost certainly contribute to the development of DS. While the authors favor a mechanical explanation related to childbirth or hysterectomy weakening the pelvic floor muscles, hormonal factors likely play a significant role as well given that nulliparous women who have not undergone hysterectomy remain at increased risk of DS compared to men. The exact pathways by which pregnancy and hysterectomy increase the risk of DS remain obscure, though hormones other than estrogen (i.e. relaxin, which is present at high levels during pregnancy) likely play a role. Like all case-control studies, this study should be viewed as hypothesis generating given the limitations inherent in such a study design. The major limitation of case-control studies is selection bias, which increases the risk of confounding by unmeasured variables. It is possible that parity and hysterectomy are simply associated with the real driver of DS development, which may not have been measured. The authors also did not include covariates such as smoking or facet and pelvic alignment parameters, and these likely play a role in DS development. Hopefully the authors will further explore their hypothesis about pelvic floor dysfunction as a risk factor for DS. The role of hormonal and structural factors should also be better understood.

Please read Dr. Cholewicki’s article on this topic in the November 1 issue. Does this change how you view risk factors for developing DS? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor


Friday, October 27, 2017

Concerns about the long-term durability of lumbar total disk replacement (TDR) along with mediocre outcomes has tempered enthusiasm for the procedure. Most of the industry-sponsored FDA trials had relatively short follow-up periods, so the long-term fate of lumbar TDRs has not been well-studied. In order to address this gap in the literature, Laugesen and colleagues from Denmark reported their long-term (average 10.6 years of follow-up) outcomes in 57 patients treated with lumbar TDR between 2003 and 2008. This represents an 84% response rate among patients still alive at the time of long-term follow-up, which is a rather impressive 10 year follow-up rate. All patients were diagnosed with degenerative disk disease (DDD) based on their baseline MRI and underwent one, two, or three level (only 1 patient underwent a 3 level procedure) lumbar TDR. The average age at surgery was 38.7 years, and 77% of patients were women. Back pain VAS improved by over 3 points on a 10 point scale, and there were significant improvements on the Dallas Pain Questionnaire. The SF-36 physical component score improved by 7 points, which is in the range of the minimally clinically important difference. About half of the patients reported they would have the operation again. One third of patients had undergone a fusion operation at the index level, and these patients had worse long-term outcomes than those who had not undergone a revision procedure. The authors did not report the rate of adjacent segment disease (ASD) or the rate of surgery at adjacent levels.

This is an interesting study as it provides a glimpse into long-term outcome following lumbar TDR. Outcomes were similar to what one would expect, with statistically significant albeit modest improvements on patient reported outcomes. The 33% rate of subsequent fusion at the index level is somewhat surprising, indicating that the re-operation rate is even higher if events at adjacent levels were to be included. In the 8-year follow-up of the SPORT degenerative spondylolisthesis cohort (most of whom underwent fusion), the overall reoperation rate was 22%, substantially less than observed in the current study. There are important limitations of this study that need to be considered, namely that there was no comparison group (i.e. a fusion cohort). Additionally, they did not report the reoperation rate for ASD, so it is hard to know if TDR actually reduces the rate of ASD. There is also no discussion of morbidity associated with TDR failure (i.e. fracture, vascular injury, need for revision anterior procedure). Despite these limitations, this paper does provide some insight into the long-term results for lumbar TDR. Overall, lumbar TDR resulted in modest improvements in patient reported outcomes and a relatively high 10 year failure rate. Surgical treatment for lumbar DDD (including both fusion and TDR) has historically had mediocre results, probably related to difficulties in accurately diagnosing the pain generator selecting the patients who are going to respond well to surgery. It seems unlikely that enthusiasm for lumbar TDR is going to increase anytime soon.


Please read Mr. Laugesen’s article on this topic in the November 1 issue. Does this change your view of lumbar TDR? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor


Friday, October 20, 2017

Surgeons typically consider one and two level cervical fusion as relatively low risk surgery with low complication rates. Due to the low rates of complications, studying the outcomes and costs associated with complications in cervical spine surgery is challenging. In order to gain a better understanding of the implications of cervical spine surgery complications, Dr. Culler and colleagues analyzed the Medicare database in order to have a sufficient number of patients to analyze these relatively rare events. From 2013-2014, the Medicare database included over 85,000 patients undergoing one or two level anterior, posterior, or anterior-posterior (AP) cervical fusion for any diagnosis. They included 10 categories of adverse events occurring during the index admission based on ICD-9 coding, ranging from dural tear to death. Overall, about 6% of patients experienced at least one complication. Similar to prior studies, risk factors for complications included age, male gender, non-white race, medical comorbidities, posterior or AP surgery, and a diagnosis of myelopathy, tumor, trauma, or infection. In unadjusted analyses, the incremental cost of having any complications was over $28,000, and the length of stay (LOS) increased by 9 days (compared to a cost of $16,000 and LOS of 2.2 days for those without a complication). In the multivariate analyses adjusted for risk factors, infection was associated with an increased cost of over $42,000 and a 14 day increased LOS, with venous thromboembolism having a similar increase in cost and LOS. Even dural tear, generally viewed as a benign complication, was associated with an increased cost of $10,000 and an increased LOS of 2.5 days.

This paper does a nice job demonstrating the effect of cervical spine surgery complications on cost and LOS. Patients with a complication had a hospitalization cost nearly three-fold higher than those without a complication and stayed in the hospital for an additional 9 days. While the overall rate of complications was relatively low at 6%, the cost associated with these 6% of patients was staggering. Prior to drawing strong conclusions, the limitations of this and all administrative database studies need to be considered. Unlike many prior Medicare database studies, this study included patients under 65 years of age, who were likely receiving Medicare benefits due to dialysis-dependence or as part of Social Security Disability. Given that over 1/3 of the patients in this study were under 65 years old, these findings may not generalize well to the traditional over age 65 Medicare population or the non-Medicare population. Additionally, the authors chose not to analyze adverse events occurring after discharge from the index admission, so most wound infections or hardware problems would not have been captured in the current study. The authors also included trauma, tumor, and infection patients with the degenerative spine population, and these patients had much higher rates of complications. The Medicare database also does not include patient reported outcomes, so it is unclear how complications affected patients in the long-term. Despite these limitations, it is clear that complications in cervical spine surgery are costly. The authors noted that bundled payment programs under consideration by CMS do not reimburse for complications, so hospitals bear the financial risk associated with complications in these models. A major concern is that adoption of such models will result in hospitals choosing not to operate on patients with more severe disease or comorbidities. While this could reduce complications and costs, it would result in the most vulnerable population losing access to care. Risk adjustment models need to be a part of any bundled payment program in order to prevent this unintended sequela.

Please read Dr. Culler’s article on this topic in the October 15 issue. Does this change how you view complications following cervical spine surgery or your thoughts on bundled payment programs? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor