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The association between lower Hounsfield units of the upper instrumented vertebra and proximal junctional kyphosis in adult spinal deformity surgery with a minimum 2-year follow-up

Ping-Guo Duan, Praveen V. Mummaneni, Joshua Rivera, Jeremy M. V. Guinn, Minghao Wang, Zhuo Xi, Bo Li, Hao-Hua Wu, Christopher P. Ames, Shane Burch, Sigurd H. Berven and Dean Chou

OBJECTIVE

Patients undergoing long-segment fusions from the lower thoracic (LT) spine to the sacrum for adult spinal deformity (ASD) correction are at risk for proximal junctional kyphosis (PJK). One mechanism of PJK is fracture of the upper instrumented vertebra (UIV) or higher (UIV+1), which may be related to bone mineral density (BMD). Because Hounsfield units (HUs) on CT correlate with BMD, the authors evaluated whether HU values were correlated with PJK after long fusions for ASD.

METHODS

The authors performed a retrospective study of patients older than 50 years who had undergone ASD correction from the LT spine to the sacrum in the period from October 2007 to January 2018 and had a minimum 2-year follow-up. Demographic and spinopelvic parameters were measured. HU values were measured on preoperative CT at the UIV, UIV+1, and UIV+2 (2 levels above the UIV) levels and were assessed for correlations with PJK.

RESULTS

The records of 127 patients were reviewed. Fifty-four patients (19 males and 35 females) with a mean age of 64.91 years and mean follow-up of 3.19 years met the study inclusion criteria; there were 29 patients with PJK and 25 patients without. There was no statistically significant difference in demographics or follow-up between these two groups. Neither was there a difference between the groups with regard to postoperative pelvic incidence (PI), sacral slope (SS), lumbar lordosis (LL), PI minus LL (PI-LL), thoracic kyphosis (TK), or sagittal vertical axis (SVA; all p > 0.05). Postoperative pelvic tilt (p = 0.003) and T1 pelvic angle (p = 0.014) were significantly higher in patients with PJK than in those without. Preoperative HUs at UIV, UIV+1, and UIV+2 were 120.41, 124.52, and 129.28 in the patients with PJK, respectively, and 152.80, 155.96, and 160.00 in the patients without PJK, respectively (p = 0.011, 0.02, and 0.018). Three receiver operating characteristic (ROC) curves for preoperative HU values at the UIV, UIV+1, and UIV+2 as a predictor for PJK were established, with areas under the ROC curve of 0.710 (95% CI 0.574–0.847), 0.679 (95% CI 0.536–0.821), and 0.681 (95% CI 0.539–0.824), respectively. The optimal HU value by Youden index was 104 HU at the UIV (sensitivity 0.840, specificity 0.517), 113 HU at the UIV+1 (sensitivity 0.720, specificity 0.517), and 110 HU at the UIV+2 (sensitivity 0.880, specificity 0.448).

CONCLUSIONS

In patients undergoing long-segment fusions from the LT spine to the sacrum for ASD, PJK was associated with lower HU values on CT at the UIV, UIV+1, and UIV+2. The measurement of HU values on preoperative CTs may be a useful adjunct for ASD surgery planning.

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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The association between lower Hounsfield units on computed tomography and cage subsidence after lateral lumbar interbody fusion

Zhuo Xi, Praveen V. Mummaneni, Minghao Wang, Huibing Ruan, Shane Burch, Vedat Deviren, Aaron J. Clark, Sigurd H. Berven and Dean Chou

OBJECTIVE

One vexing problem after lateral lumbar interbody fusion (LLIF) surgery is cage subsidence. Low bone mineral density (BMD) may contribute to subsidence, and BMD is correlated with Hounsfield units (HUs) on CT. The authors investigated if lower HU values correlated with subsidence after LLIF.

METHODS

A retrospective study of patients undergoing single-level LLIF with pedicle screw fixation for degenerative conditions at the University of California, San Francisco, by 6 spine surgeons was performed. Data on demographics, cage parameters, preoperative HUs on CT, and postoperative subsidence were collected. Thirty-six–inch standing radiographs were used to measure segmental lordosis, disc space height, and subsidence; data were collected immediately postoperatively and at 1 year. Subsidence was graded using a published grade of disc height loss: grade 0, 0%–24%; grade I, 25%–49%; grade II, 50%–74%; and grade III, 75%–100%. HU values were measured on preoperative CT from L1 to L5, and each lumbar vertebral body HU was measured 4 separate times.

RESULTS

After identifying 138 patients who underwent LLIF, 68 met the study inclusion criteria. All patients had single-level LLIF with pedicle screw fixation. The mean follow-up duration was 25.3 ± 10.4 months. There were 40 patients who had grade 0 subsidence, 15 grade I, 9 grade II, and 4 grade III. There were no significant differences in age, sex, BMI, or smoking. There were no significant differences in cage sizes, cage lordosis, and preoperative disc height. The mean segmental HU (the average HU value of the two vertebrae above and below the LLIF) was 169.5 ± 45 for grade 0, 130.3 ± 56.2 for grade I, 100.7 ± 30.2 for grade II, and 119.9 ± 52.9 for grade III (p < 0.001). After using a receiver operating characteristic curve to establish separation criteria between mild and severe subsidence, the most appropriate threshold of HU value was 135.02 between mild and severe subsidence (sensitivity 60%, specificity 92.3%). After univariate and multivariate analysis, preoperative segmental HU value was an independent risk factor for severe cage subsidence (p = 0.017, OR 15.694, 95% CI 1.621–151.961).

CONCLUSIONS

Lower HU values on preoperative CT are associated with cage subsidence after LLIF. Measurement of preoperative HU values on CT may be useful when planning LLIF surgery.

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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Association between timing of kyphoplasty and opioid prescribing risk after vertebral fracture

Jay K. Nathan, Mitchell A. Johnson, Jennifer F. Waljee, Nicholas Szerlip, Paul Park and Mark E. Oppenlander

OBJECTIVE

Approximately 550,000 Americans experience vertebral fracture annually, and most receive opioids to treat the resulting pain. Kyphoplasty of the fractured vertebra is a procedural alternative that may mitigate risks of even short-term opioid use. While reports of kyphoplasty’s impact on pain scores are mixed, no large-scale data exist regarding opioid prescribing before and after the procedure. This study was conducted to determine whether timing of kyphoplasty following vertebral fracture is associated with duration or intensity of opioid prescribing.

METHODS

This retrospective cohort study used 2001–2014 insurance claims data from a single, large private insurer in the US across multiple care settings. Patients were adults with vertebral fractures who were prescribed opioids and underwent balloon-assisted kyphoplasty within 4 months of fracture. Opioid overdose risk was stratified by prescribed average daily morphine milligram equivalents using CDC guidelines. Filled prescriptions and risk categories were evaluated at baseline and 90 days following kyphoplasty.

RESULTS

Inclusion criteria were met by 7119 patients (median age 77 years, 71.7% female). Among included patients, 3505 (49.2%) were opioid naïve before fracture. Of these patients, 31.1% had new persistent opioid prescribing beyond 90 days after kyphoplasty, and multivariable logistic regression identified kyphoplasty after 8 weeks as a predictor (OR 1.34, 95% CI 1.02–1.76). For patients previously receiving opioids, kyphoplasty > 4 weeks after fracture was associated with persistently elevated prescribing risk (OR 1.84, 95% CI 1.23–2.74).

CONCLUSIONS

New persistent opioid prescribing occurred in nearly one-third of patients undergoing kyphoplasty after vertebral fracture, although early treatment was associated with a reduction in this risk. For patients not naïve to opioids before fracture diagnosis, early kyphoplasty was associated with less persistent elevation of opioid overdose risk. Subsequent trials must compare opioid use by vertebral fracture patients treated via operative (kyphoplasty) and nonoperative (ongoing opioid) strategies before concluding that kyphoplasty lacks value, and early referral for kyphoplasty may be appropriate to avoid missing a window of efficacy.

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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Association of osteopenia and osteoporosis with higher rates of pseudarthrosis and revision surgery in adult patients undergoing single-level lumbar fusion

Syed I. Khalid, Ravi S. Nunna, Samantha Maasarani, Erika Belmont, Palvasha Deme, Sai Chilakapati, Cody Eldridge, Ravinderjit Singh, Carlos A. Bagley and Owoicho Adogwa

OBJECTIVE

Patients with osteopenia or osteoporosis who require surgery for symptomatic degenerative spondylolisthesis may have higher rates of postoperative pseudarthrosis and need for revision surgery than patients with normal bone mineral densities (BMDs). To this end, the authors compared rates of postoperative pseudarthrosis and need for revision surgery following single-level lumbar fusion in patients with normal BMD with those in patients with osteopenia or osteoporosis. The secondary outcome was to investigate the effects of pretreatment with medications that prevent bone loss (e.g., teriparatide, bisphosphonates, and denosumab) on these adverse outcomes in this patient cohort.

METHODS

Patients undergoing single-level lumbar fusion between 2007 and 2017 were identified. Based on 1:1 propensity matching for baseline demographic characteristics and comorbidities, 3 patient groups were created: osteopenia (n = 1723, 33.3%), osteoporosis (n = 1723, 33.3%), and normal BMD (n = 1723, 33.3%). The rates of postoperative pseudarthrosis and revision surgery were compared between groups.

RESULTS

The matched populations analyzed in this study included a total of 5169 patients in 3 groups balanced at baseline, with equal numbers (n = 1723, 33.3%) in each group: patients with a history of osteopenia, those with a history of osteoporosis, and a control group of patients with no history of osteopenia or osteoporosis and with normal BMD. A total of 597 complications were recorded within a 2-year follow-up period, with pseudarthrosis (n = 321, 6.2%) being slightly more common than revision surgery (n = 276, 5.3%). The odds of pseudarthrosis and revision surgery in patients with osteopenia were almost 2-fold (OR 1.7, 95% CI 1.26–2.30) and 3-fold (OR 2.73, 95% CI 1.89–3.94) higher, respectively, than those in patients in the control group. Similarly, the odds of pseudarthrosis and revision surgery in patients with osteoporosis were almost 2-fold (OR 1.92, 95% CI 1.43–2.59) and > 3-fold (OR 3.25, 95% CI 2.27–4.65) higher, respectively, than those in patients in the control group. Pretreatment with medications to prevent bone loss prior to surgery was associated with lower pseudarthrosis and revision surgery rates, although the differences did not reach statistical significance.

CONCLUSIONS

Postoperative pseudarthrosis and revision surgery rates following single-level lumbar spinal fusion are significantly higher in patients with osteopenia and osteoporosis than in patients with normal BMD. Pretreatment with medications to prevent bone loss prior to surgery decreased these complication rates, although the observed differences did not reach statistical significance.

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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Do we underdiagnose osteoporosis in patients with pyogenic spondylodiscitis?

Christoph Bettag, Tammam Abboud, Christian von der Brelie, Patrick Melich, Veit Rohde and Bawarjan Schatlo

OBJECTIVE

Pyogenic spondylodiscitis affects a fragile patient population. Surgical treatment in cases of instability entails instrumentation, and loosening of this instrumentation is a frequent occurrence in pyogenic spondylodiscitis. The authors therefore attempted to investigate whether low bone mineral density (BMD)—which is compatible with the diagnosis of osteoporosis—is underdiagnosed in patients with pyogenic spondylodiscitis. How osteoporosis was treated and how it affected implant stability were further analyzed.

METHODS

Charts of patients who underwent operations for pyogenic spondylodiscitis were retrospectively reviewed for clinical data, prior medical history of osteoporosis, and preoperative CT scans of the thoracolumbar spine. In accordance with a previously validated high-fidelity opportunistic CT assessment, average Hounsfield units (HUs) in vertebral bodies of L1 and L4 were measured. Based on the validation study, the authors opted for a conservative cutoff value for low BMD, being compatible with osteoporosis ≤ 110 HUs. Baseline and outcome variables, including implant failure and osteoporosis interventions, were entered into a multivariate logistic model for statistical analysis.

RESULTS

Of 200 consecutive patients who underwent fusion surgery for pyogenic spondylodiscitis, 64% (n = 127) were male and 66% (n = 132) were older than 65 years. Seven percent (n = 14) had previously been diagnosed with osteoporosis. The attenuation analysis revealed HU values compatible with osteoporosis in 48% (95/200). The need for subsequent revision surgery due to implant failure showed a trend toward an association with estimated low BMD (OR 2.11, 95% CI 0.95–4.68, p = 0.067). Estimated low BMD was associated with subsequent implant loosening (p < 0.001). Only 5% of the patients with estimated low BMD received a diagnosis and pharmacological treatment of osteoporosis within 1 year after spinal instrumentation.

CONCLUSIONS

Relying on past medical history of osteoporosis is insufficient in the management of patients with pyogenic spondylodiscitis. This is the first study to identify a substantially missed opportunity to detect osteoporosis and to start pharmacological treatment after surgery for prevention of implant failure. The authors advocate for routine opportunistic CT evaluation for a better estimation of bone quality to initiate diagnosis and treatment for osteoporosis in these patients.

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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Does the use of preoperative bisphosphonates in patients with osteopenia and osteoporosis affect lumbar fusion rates? Analysis from a national spine registry

Kern H. Guppy, Priscilla H. Chan, Heather A. Prentice, Elizabeth P. Norheim, Jessica E. Harris and Harsimran S. Brara

OBJECTIVE

Bisphosphonates are used to increase bone strength in treating osteopenia and osteoporosis, but their use for increasing lumbar fusion rates has been controversial. The objective of this study was to determine if preoperative treatment with bisphosphonates affects the reoperation rates for nonunions (operative nonunion rates) following lumbar fusions in patients with osteopenia or osteoporosis.

METHODS

The authors conducted a cohort study using data from the Kaiser Permanente Spine Registry. Patients (aged ≥ 50 years) with a diagnosis of osteopenia or osteoporosis who underwent primary elective lumbar fusions for degenerative disc disease, deformity, or spondylolisthesis were included in the cohort. Repeated spinal procedures at the index lumbar levels were noted through chart review. Reoperations for symptomatic nonunions (operative nonunions), time to nonunion, and the nonunion spine level(s) were also identified. The crude 2-year cumulative incidence of operative nonunions was calculated as 1 minus the Kaplan-Meier estimator. Cox proportional hazard regression was used to evaluate the association between preoperative bisphosphonate use and operative nonunion after adjustment for covariates. Analysis was stratified by osteopenia and osteoporosis diagnosis.

RESULTS

The cohort comprised 1040 primary elective lumbar fusion patients, 408 with osteopenia and 632 with osteoporosis. Ninety-seven (23.8%) patients with osteopenia and 370 (58.5%) patients with osteoporosis were preoperative bisphosphonate users. For the osteopenia group, no operative nonunions were observed in patients with preoperative bisphosphonate, while the crude 2-year incidence was 2.44% (95% CI 0.63–4.22) in the nonuser group. For the osteoporotic group, after adjustment for covariates, no difference was observed in risk for operative nonunions between the preoperative bisphosphonate users and nonusers (HR 0.96, 95% CI 0.20–4.55, p = 0.964).

CONCLUSIONS

To the authors’ knowledge, this study presents one of the largest series of patients with the diagnosis of osteopenia or osteoporosis in whom the effects of preoperative bisphosphonates on lumbar fusions were evaluated using operative nonunion rates as an outcome measure. The results indicate that preoperative bisphosphonate use had no effect on the operative nonunion rates for patients with osteoporosis. Similar indications were not confirmed in osteopenia patients because of the low nonunion frequency. Further studies are warranted to the determine if preoperative and postoperative timing of bisphosphonate use has any effect on lumbar fusion rates.

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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Editorial. Bisphosphonates do not impair spinal fusion

Paul A. Anderson and Brett A. Freedman

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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Editorial. Is preoperative bone health assessment and optimization in spine surgery a good idea?

Timothy F. Witham, Ethan Cottrill and Zach Pennington

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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Hounsfield units of the vertebral body and pedicle as predictors of pedicle screw loosening after degenerative lumbar spine surgery

Fei Xu, Da Zou, Weishi Li, Zhuoran Sun, Shuai Jiang, Siyu Zhou and Zhuofu Li

OBJECTIVE

The authors aimed to compare the efficacy of lumbar vertebral body Hounsfield units (HUs) and pedicle HUs at predicting pedicle screw loosening.

METHODS

The authors retrospectively assessed 143 patients with L3–5 instrumentation. The patients were classified into one of two groups based on the status of their L3 screws (a screw loosening group or a control group). The pedicle HUs and vertebral HUs of L3 were measured using preoperative lumbar CT scans, and the pedicle HUs were measured in two ways: by excluding or by including cortical bone.

RESULTS

The screw loosening rate was 20.3% (n = 29/143) at the 12-month follow-up. The vertebral body HUs and pedicle HUs in the screw loosening group were lower than those in the control group (vertebral body group: 98.6 HUs vs 121.4 HUs, p < 0.001; pedicle excluding cortical bone: 208.9 HUs vs 290.5 HUs, p = 0.002; pedicle including cortical bone: 249.4 HUs vs 337.5 HUs, p < 0.001). The pedicle HUs tended to have a higher area under the receiver operating characteristic curve value in predicting screw loosening, compared with that of vertebral body HUs, but the difference was not statistically significant (p > 0.05). Among patients with low vertebral body HUs of ≤ 130, the loosening rate was much lower in patients with pedicle HUs of ≤ 340 than in those with pedicle HUs of > 340 (31.0% vs 13.0%, respectively; p < 0.05).

CONCLUSIONS

Vertebral body HUs alone are insufficient to accurately evaluate the risk of pedicle screw loosening. Therefore, it is important to collect both the pedicle HU and vertebral body HU measurements for surgical planning.

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis

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Introduction. Lumbar spinal osteoporosis

Paul A. Anderson, Brett A. Freedman, Dean Chou and Timothy Witham

In Neurosurgical Focus Volume 49 (2020): Issue 2 (Aug 2020): Lumbar Spinal Osteoporosis