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Preoperative Assessment of Bone Quality in Spine Deformity Surgery

Correlation With Clinical Practice and Published Recommendations

Kuprys, Tomas K., MD; Steinmetz, Leah M., BA; Fischer, Charla R., MD; Protopsaltis, Themistocles S., MD; Passias, Peter G., MD; Goldstein, Jeffrey A., MD; Bendo, John A., MD; Errico, Thomas J., MD; Buckland, Aaron J., MBBS, FRAC

doi: 10.1097/BRS.0000000000002956
DEFORMITY
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Study Design. Retrospective cohort study.

Objective. The goals of this study were to (A) evaluate preoperative bone quality assessment and intervention practice over time and (B) review the current evidence for bone evaluation in spine fusion surgery.

Summary of Background Data. Deformity spine surgery has demonstrated improved quality of life in patients; however, its cost has made it controversial. If preoperative bone quality can be optimized then potentially these treatments could be more durable; however, at present, no clinical practice guidelines have been published by professional spine surgical organizations.

Methods. A retrospective cohort review was performed on patients who underwent a minimum five-level primary or revision fusion. Preoperative bone quality metrics were evaluated over time from 2012 to 2017 to find potential trends. Subgroup analysis was conducted based on age, sex, preoperative diagnosis, and spine fusion region.

Results. Patient characteristics including preoperative rates of pseudarthrosis and junctional failure did not change. An increasing trend of physician bone health documentation was noted (P = 0.045) but changes in other metrics were not significant. A sex bias favored females who had higher rates of preoperative DXA studies (P = 0.001), Vitamin D 25-OH serum labs (P = 0.005), Vitamin D supplementation (P = 0.022), calcium supplementation (P < 0.001), antiresorptive therapy (P = 0.016), and surgeon clinical documentation of bone health (P = 0.008) compared with men.

Conclusion. Our spine surgeons have increased documentation of bone health discussions but this has not affected bone quality interventions. A discrepancy exists favoring females over males in nearly all preoperative bone quality assessment metrics. Preoperative vitamin D level and BMD assessment should be considered in patients undergoing long fusion constructs; however, the data for bone anabolic and resorptive agents have less support. Clinical practice guidelines on preoperative bone quality assessment spine patients should be defined.

Level of Evidence: 4

Preoperative assessment of bone quality could improve long fusion construct durability. Our spine surgeons have increased documentation of bone health discussions but this has not affected bone quality interventions. A discrepancy exists favoring females over males in nearly all preoperative bone quality metrics.

Department of Orthopedic Surgery, NYU Langone Orthopedic Hospital, NYU Langone Health, New York, NY.

Address correspondence and reprint requests to Tomas K. Kuprys, MD, Regenerative Orthopaedics and Spine Institute, 135 North Park Place, Suite 101, Stockbridge, GA 30281; E-mail: tkuprys@rosi.us

Received 29 August, 2018

Revised 28 October, 2018

Accepted 19 November, 2018

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

Relevant financial activities outside the submitted work: consultancy, grants.

Deformity spine surgery has demonstrated improved quality of life outcomes; however, associated treatment cost has generated increased scrutiny. Cost-effectiveness analyses hinge on the longevity of this treatment1–3 with some breakeven threshold estimates suggesting a minimum construct durability of 5 years.4,5 Reported revision rates up to 20% at 2 years and construct failure estimates above 40% at 4 years raise questions about achieving such durability.6–11 If surgeons preoperatively optimize bone quality to improve fixation, interbody support, and successful fusion then revision rates may be lowered.12–15 In 2009 a survey study of spine specialists reported a lack of routine bone quality evaluation in fusion candidates and advocated for increased awareness16 which is critical in a surgical population with a sizeable potential for undiagnosed osteoporosis.17

While spine surgeons have provided expert recommendations,18–22 no clinical practice guidelines on bone quality assessment exist from international professional spinal surgery organizations yet interestingly nonsurgical bone health specialists have begun to assess their role in presurgical optimization.23 We aim to advance a dialogue on a preoperative bone quality risk modification protocol beginning with an analysis of our institution's utilization of preoperative bone quality metrics and then review the evidence to reveal where standardized improvements could be made. The purpose of our study is to garner a baseline of how surgeons are implementing these concepts and to identify if there are positive trends in practice reflecting new evidence and expert recommendations for bone health optimization.

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MATERIALS AND METHODS

Patient Selection

A retrospective cohort review was performed at a single surgical practice of eight spine surgeons on patients who underwent a minimum five-level primary or revision fusion between November 2012 and March 2017. In order to follow trends over time, patients were grouped into 12-month periods except the initial time period which is 17-months. Exclusion criteria were age < 40 years at time of surgery and surgical case indications of trauma, infection, neuromuscular condition, and tumor.

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Preoperative Bone Quality Assessment

Bone quality assessment was quantified by the frequency that the following data were available in the medical record prior to the patient undergoing surgery: bone densitometry (DXA), Vitamin D 25-hydroxy serum lab, Vitamin D supplementation, calcium supplementation, bone anabolic agent use, bone antiresorptive agent use, referral to or under active care of a bone health specialist, and documentation in the surgeon's clinical note of a bone health discussion. Differences in preoperative practices were stratified by age, sex, BMI, spine region fused, and preoperative diagnoses of junctional failure or pseudarthrosis.

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Statistical Analysis

Statistical analysis was completed with the SPSS software package (version 23.0; Armonk, NY: IBM). Trend analysis in practice patterns was assessed with Linear by Linear Association (LLA) Mantel–Haenzsel tests. Differences between groups were examined with t test and chi-square tests. Significance was defined as P value < 0.05.

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RESULTS

Three hundred fourteen patients met the inclusion criteria during the study time period. For the entire cohort, mean age was 63.2 ± 10.3 years, with 65.3% female, BMI 28.0 ± 6.2, and 56.4% having had previous spine surgery. The preoperative diagnosis was pseudarthrosis in 18.8% of patients and junctional failure in 9.2%. There were no significant trend changes in these preoperative demographic variables among the study time periods (Table 1). The only preoperative bone quality assessment metric that had a significant linear trend over the study time period was an increased rate of surgeon documentation of patient's bone health (P = 0.045). None of the other bone quality assessment preoperative utilization rates changed significantly over the 5-year study duration (Table 2).

TABLE 1

TABLE 1

TABLE 2

TABLE 2

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Pseudarthrosis and Junctional Failure Subgroup

Patient subgroups with a preoperative diagnosis of pseudarthrosis or junctional failure did not demonstrate any significant trends in preoperative metrics. When these two groups were compared with a control group from this cohort without these diagnoses, the only significant finding was that the pseudarthrosis group had a lower Vitamin D 25-OH serum lab rates (1.9% [0.0%, 0.0%, 0.0%, 7.1%] vs. 14.7% [4.4%, 28.8%, 10.5%, 18.5%]; P = 0.009). The junctional failure diagnosis group bone quality metric rates were not different from the control group.

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Gender Stratified Subgroup

Subgroup analysis by gender demonstrated an increased trend in the rate of preoperative DXA studies for men (P = 0.030) driven by no male patients obtaining a preoperative DXA study in the initial time period compared with approximately 18% in subsequent time periods. Female rates of preoperative bone quality assessment were unchanged over the study duration. Comparing male and female groups, female patients had significantly higher rates of preoperative DXA studies (P = 0.001), Vitamin D 25-OH serum labs (P = 0.005), Vitamin D supplementation (P = 0.022), calcium supplementation (P < 0.001), antiresorptive therapy (P = 0.016), and surgeon clinical documentation of bone health (P = 0.008). No difference in anabolic bone therapy or bone health specialist referrals was noted between men and women (Table 2).

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Age Stratified Subgroup

Subgroup analysis of patients younger and older than 65 years of age did not demonstrate any significant trends over the duration of the study. However, between these two groups the older subgroup had significantly higher preoperative rates of DXA studies (P = 0.003) and antiresorptive treatment (P = 0.003) with the remaining preoperative assessment not being statistically different (Table 2). Using published guidelines for preventative osteoporosis screening of women > 65 years and men > 70 years our study group demonstrated that 35% of indicated women and 19% of indicated men had met these recommendations.

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Spine Region Stratified Subgroup

Subgroup analysis of patients comparing proximal fusions (cervical, cervicothoracic) and distal fusions (thoracic, thoracolumbar, cervicothoracolumbar) did not demonstrate any significant difference in pre-operative bone quality assessment trends within or between these two groups (Table 3).

TABLE 3

TABLE 3

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DISCUSSION

Our results demonstrate an increase in bone quality awareness through physician clinical documentation however there was no correlate in increased preoperative evaluation, referral, or treatment. A gender bias in preoperative DXA, Vitamin D lab, Vitamin D and calcium supplementation, antiresorptive therapy, and bone quality discussion favored females. Osteoporosis prevalence has been reported as greater than 50% in women age > 50 years undergoing elective spine surgery compared with a 15% rate in men,24 but perhaps more importantly, the success of the Women's Health Initiative and, over the past decade, its continuing extension studies have increased global awareness of women's health concerns.25 In our cohort, men demonstrated an increase in DXA rates over time; however, this lagged behind the female subgroup and is mainly a reflection of no male patients receiving a preoperative DXA in the baseline time period. Not surprisingly patients over age 65 had significantly higher rates of DXA assessment and antiresorptive treatment compared with younger patients given the increased prevalence of osteoporosis with age. When surgical cases were grouped by anatomic region fused no differences were noted in preoperative assessments possibly indicating that surgeons are more concerned with the key patient demographics of age and gender in contrast to the spine region undergoing fusion when considering bone quality.

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Bone Mineral Density (BMD) and DXA

Guidelines by the National Osteoporosis Foundation, US Preventive Services Task Force, and American College of Radiology endorse osteoporosis screening with DXA in women age > 65 years and men age > 70 years.19 Based upon these criteria, the indicated DXA rates in our study cohort of 35% for women and 19% for men would be considered inadequate. Furthermore, the high prevalence of osteoporosis in women age > 50 years undergoing elective spine surgery could support younger patient screening in a spine surgical cohort. Beyond these guidelines, no official spine surgical society recommendations exist for preoperative screening of BMD.

Several surgeon opinions have offered preoperative BMD screening recommendations for elective spine fusions.18–21 A spine surgeon survey noted that 44% of surgeons would obtain a preoperative DXA study for an instrumented fusion procedure and the authors concluded that this survey result indicates further needed education on bone health.16 The identification of patients at risk for low BMD by a medical history of menopause, rheumatologic conditions, and chronic steroid, anticoagulant, or proton pump inhibitor usage should result in a DXA assessment and referral to a bone health specialist prior to spine surgery.21

Published literature suggests that low BMD, even if not osteoporotic range (T-score < −2.5), can negatively impact fusion constructs. A retrospective study of single-level interbody cases found graft subsidence was associated with T-score < −1.0.13 A retrospective spine deformity cohort had increased risk of proximal junctional kyphosis not only in patients with T-score < −2.5 but even in those with T-score < −1.5.14,15 Some authors have proposed that patients with a T-score < −2 should postpone surgery until treated for 6 weeks with a bone anabolic agent, patients with a T-score < −3 should postpone surgery until a repeat DXA shows improved BMD, and patients with a T-score < -4 should not undergo pedicle fixation or possibly incorporate augmented fixation techniques.26

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Vitamin D

Vitamin D deficiency prevalence rates can be 25% to 50% in common clinical populations and recent studies evaluating perioperative Vitamin D levels in elective spine fusion populations have demonstrated similar insufficiency rates of 39% to 57% and deficiency rates of 27% to 30% with increased BMI and lack of Vitamin D supplementation associated with deficiency.27–29 Authors have proposed optimal Vitamin D levels of 30 to 60 ng/mL,30,31 insufficiency < 30 ng/mL, and deficiency < 20 to 25 ng/mL.27,28 A prospective observational cohort analysis of elective spine fusion found Vitamin D deficiency to be an independent risk factor for nonunion at one year and both Vitamin D insufficiency and deficiency to be associated with longer time to fusion.12 In our study the prevalence of preoperative Vitamin D testing of 11.5% is similar to a survey response of 12% of spine surgeons advocating for checking Vitamin D labs in spine fusion patients.16

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Supplementation With Vitamin D and Calcium

In our cohort approximately one-third of the patients received Vitamin D supplementation and one-third received calcium supplementation however given that our study is retrospective the data capture within the medical record of specific supplement formulations and dosages oftentimes was generically labeled which limited analysis. Consistent with our other findings female patients had a greater frequency of both Vitamin D and calcium supplementation preoperatively. Age-based subgroup analysis showed no difference in supplementation rates which is surprising given the increased incidence of Vitamin D deficiency with age.

Vitamin D and calcium supplementation must be taken in the context of a patient's endogenous generation and exogenous intake of this vitamin. Factors such as demographics, sun exposure, ethnic background, and geographic locale impact serum levels31,32 and thus in our study cohort it was difficult to assess whether supplementation was indicated without Vitamin D serum level data. In general, Vitamin D supplementation either at 600 to 2000 IU daily or repletion for severe deficiency at 50,000 IU weekly must be taken in concert with calcium 1000 to 2000 mg daily18,20,31,33 with some authors even suggesting empiric supplementation.31

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Bone Anabolic Agents

Teriparatide (recombinant PTH) and abaloparatide (recombinant PTHrP) are the two most common medications used to actively induce bone formation. While generally prescribed by endocrinologists for the treatment of osteoporosis, their potential to improve fixation resilience in prospective studies by increasing BMD, decreasing Type-2 junctional failure, increasing pedicle screw insertional torque, and decreasing pedicle screw loosening has garnered interest from spine surgeons.34,35

Two systematic review articles analyzed the published literature on teriparatide in spine fusion clinical studies with one suggesting possible fusion enhancement in osteoporotic women and implied a need to expand study to include male subjects36 while the second article recommended caution when interpreting teriparatide studies because of the low sample sizes and nonuniform study formats.37 In addition, several of the discussed studies did not have a formal control group and instead compared teriparatide to bisphosphonate treatment arms for unclear reasons. This unfortunately limits an independent understanding of how effective anabolic bone agent treatments are in improving fusion outcomes.

In the past year new Level 1 evidence from an industry sponsored study in osteoporotic females receiving teriparatide and undergoing TLIF/PLIF demonstrated earlier fusion rates, lower bone turnover serum markers, and no difference in 6-month patient reported outcomes compared with controls.38 In our study the overall incidence of preoperative bone anabolic treatment was the lowest of all metrics at 4.1% and one of the few metrics without a gender bias. Such a low rate of utilization may imply surgeons are not convinced of its efficacy or patients may not be willing to use it. Specifically issues of teriparatide cost, frequency, dosing, duration, subcutaneous administration, and a potential increased risk of osteosarcoma unproven in human studies have been cited as reasons against its use.39

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Bone Antiresorptives

Bisphosphonate therapy has been a controversial adjunct to spine surgery given a concern that limiting osteoclasts resorptive behavior may also limit the remodeling process of fusion. Recent reviews evaluated the literature with limited findings because of study heterogeneity with several studies comparing bisphosphonates to teriparatide, bisphosphonates to Vitamin D supplementation, and lack of reported fusion rates.36,37 A prospective randomized placebo-controlled trial of zoledronate in osteoporotic patients undergoing single-level PLIF demonstrated a decreased time to and rate of fusion, increased BMD, and improved Oswestry Disability Index scores at 9 and 12 months compared with controls.40 A second prospective trial compared alendronate to teriparatide in osteoporotic women undergoing PLIF and found no difference in outcomes and fusion rates but noted a faster time to union and increased BMD in the teriparatide group.41 From these studies bisphosphonates clearly do not impart a fusion impediment and thus could likely be continued through a spine fusion procedure in osteoporotic patients. While several studies comparing bisphosphonates and bone anabolic agents have been published it is not quite clear that these medications should be considered a control for the other and in fact future research may benefit from assessing their synergy given the different mechanisms of each for treating osteoporosis.

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Bone Health Referral

Many medical institutions now have a dedicated bone health team available for consultation usually within a division of Endocrinology, Primary Care, or Rheumatology. Several authors advocate referral to a bone health team for any patients at the earliest spine clinic visit where surgical fixation is considered, in particular for those with a diagnosis of osteoporosis or risk factors.16–21,36 As reported earlier the prevalence of undiagnosed osteoporosis in general and particularly in women undergoing elective spine fusion would imply that our overall preoperative referral rate to a bone health consultant of 10.2% of female patients and 4.6% of men likely underdiagnoses osteoporosis in our long fusion cohort.17,24

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Limitations and Future Directions

The inherent limitations of a retrospective study are acknowledged in particular the difficulty of obtaining accurate numerical data on medication dosing. The heterogeneity of the cohort adds variability in terms of construct length and surgical history as some patients had no, one, or several surgeries prior to the long fusion constructs that they underwent in the study time period. This study did successfully provide a view of which preoperative bone quality data are available for surgeons and at what rates these data are being obtained. Future directions should include prospective analysis of when and why spine surgeons select certain bone quality metrics. Development of a national-level spine society protocol that guides preoperative bone quality evaluation for long fusion constructs should improve outcomes based on the above data and thereby improve the cost-benefit proposition to healthcare consumers while fulfilling our duty as physicians to reduce surgical patient risk.

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CONCLUSION

Our spine surgeons have increased documentation of bone health discussions but not preoperative bone quality interventions in long fusion constructs. A discrepancy exists favoring females over males in nearly all the preoperative bone quality assessment metrics. Preoperative Vitamin D level and DXA study are recommended for elective spine patients given the prevalence of hypovitaminosis D and undiagnosed osteoporosis in this group. Bisphosphonates do not hinder fusion and some data suggest an improved fusion rate. The mixed quality of studies on bone anabolic agents requires further research regarding spine fusion effectiveness. Development of a long fusion bone health pathway in partnership with nonsurgical bone health specialists may produce more consistent preoperative optimization. Lastly, clinical practice guidelines for preoperative bone quality assessment and treatment should be defined by spine surgeon professional societies.

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References

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Keywords:

antiresorptives; bone anabolic agents; bone health; bone quality; calcium; deformity; DXA/DEXA; fusion; guidelines; osteoporosis; spine surgery; Vitamin D

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