Predicting development of severe clinically relevant distal junctional kyphosis following adult cervical deformity surgery, with further distinction from mild asymptomatic episodes

Peter G. PassiasDepartment of Orthopedic Surgery, NYU Langone Orthopedic Hospital, New York, New York;

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Sara NaessigDepartment of Orthopedic Surgery, NYU Langone Orthopedic Hospital, New York, New York;

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Nicholas KummerDepartment of Orthopedic Surgery, NYU Langone Orthopedic Hospital, New York, New York;

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Lara PassfallDepartment of Orthopedic Surgery, NYU Langone Orthopedic Hospital, New York, New York;

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Renaud LafageDepartment of Orthopedic Surgery, Hospital for Special Surgery, New York, New York;

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Virginie LafageLenox Hill Hospital, Northwell Health, Department of Orthopaedics, New York, New York;

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Breton LineDepartment of Spine Surgery, Denver International Spine Clinic, Presbyterian St. Luke’s/Rocky Mountain Hospital for Children, Denver, Colorado;

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Bassel G. DieboDepartment of Orthopedics, SUNY Downstate Medical Center, Brooklyn, New York;

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Themistocles ProtopsaltisDepartment of Orthopedic Surgery, NYU Langone Orthopedic Hospital, New York, New York;

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Han Jo KimDepartment of Orthopedic Surgery, Hospital for Special Surgery, New York, New York;

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Robert EastlackDivision of Orthopaedic Surgery, Scripps Clinic, La Jolla, California;

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Alex SoroceanuDepartment of Orthopaedic Surgery, University of Calgary, Alberta, Canada;

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Eric O. KlinebergDepartment of Orthopaedic Surgery, University of California, Davis, California;

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Robert A. HartDepartment of Orthopedic Surgery, Swedish Neuroscience Institute, Seattle, Washington;

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Douglas BurtonDepartment of Orthopaedic Surgery, University of Kansas Medical Center, Kansas City, Kansas;

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Shay BessDepartment of Spine Surgery, Denver International Spine Clinic, Presbyterian St. Luke’s/Rocky Mountain Hospital for Children, Denver, Colorado;

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Frank SchwabLenox Hill Hospital, Northwell Health, Department of Orthopaedics, New York, New York;

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Christopher I. ShaffreyDepartment of Neurosurgery, Duke University Medical Center, Durham, North Carolina;

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Justin S. SmithDepartment of Neurosurgery, University of Virginia Medical Center, Charlottesville, Virginia; and

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Christopher P. AmesDepartment of Neurological Surgery, University of California, San Francisco, California

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OBJECTIVE

This retrospective cohort study aimed to develop a formal predictive model distinguishing between symptomatic and asymptomatic distal junctional kyphosis (DJK). In this study the authors identified a DJK rate of 32.2%. Predictive models were created that can be used with high reliability to help distinguish between severe symptomatic DJK and mild asymptomatic DJK through the use of surgical factors, radiographic parameters, and patient variables.

METHODS

Patients with cervical deformity (CD) were stratified into asymptomatic and symptomatic DJK groups. Symptomatic: 1) DJK angle (DJKA) > 10° and either reoperation due to DJK or > 1 new-onset neurological sequela related to DJK; or 2) either a DJKA > 20° or ∆DJKA > 20°. Asymptomatic: ∆DJK > 10° in the absence of neurological sequelae. Stepwise logistic regressions were used to identify factors associated with these types of DJK. Decision tree analysis established cutoffs.

RESULTS

A total of 99 patients with CD were included, with 32.2% developing DJK (34.3% asymptomatic, 65.7% symptomatic). A total of 37.5% of asymptomatic patients received a reoperation versus 62.5% symptomatic patients. Multivariate analysis identified independent baseline factors for developing symptomatic DJK as follows: pelvic incidence (OR 1.02); preoperative cervical flexibility (OR 1.04); and combined approach (OR 6.2). Having abnormal hyperkyphosis in the thoracic spine, more so than abnormal cervical lordosis, was a factor for developing symptomatic disease when analyzed against asymptomatic patients (OR 1.2). Predictive modeling identified factors that were predictive of symptomatic versus no DJK, as follows: myelopathy (modified Japanese Orthopaedic Association score 12–14); combined approach; uppermost instrumented vertebra C3 or C4; preoperative hypermobility; and > 7 levels fused (area under the curve 0.89). A predictive model for symptomatic versus asymptomatic disease (area under the curve 0.85) included being frail, T1 slope minus cervical lordosis > 20°, and a pelvic incidence > 46.3°. Controlling for baseline deformity and disability, symptomatic patients had a greater cervical sagittal vertical axis (4–8 cm: 47.6% vs 27%) and were more malaligned according to their Scoliosis Research Society sagittal vertical axis measurement (OR 0.1) than patients without DJK at 1 year (all p < 0.05). Despite their symptomatology and higher reoperation rate, outcomes equilibrated in the symptomatic cohort at 1 year following revision.

CONCLUSIONS

Overall, 32.2% of patients with CD suffered from DJK. Symptomatic DJK can be predicted with high reliability. It can be further distinguished from asymptomatic occurrences by taking into account pelvic incidence and baseline cervicothoracic deformity severity.

ABBREVIATIONS

AUC = area under the curve; CBVA = chin-brow vertical angle; CD = cervical deformity; CL = cervical lordosis; cSVA = cervical SVA; DJK = distal junctional kyphosis; DJKA = DJK angle; EQ-5D = EuroQol-5D health survey; HRQOL = health-related quality of life; LIV = lowest instrumented vertebra; LL = lumbar lordosis; mJOA = modified Japanese Orthopaedic Association; NDI = Neck Disability Index; NRS = numeric rating scale; PI = pelvic incidence; PI-LL = PI-LL mismatch; PJK = proximal junctional kyphosis; PT = pelvic tilt; SRS = Scoliosis Research Society; SS = sacral slope; SVA = sagittal vertical axis; TK = thoracic kyphosis; TS−CL = T1 slope minus CL; UIV = uppermost instrumented vertebra; VAS = visual analog scale.

OBJECTIVE

This retrospective cohort study aimed to develop a formal predictive model distinguishing between symptomatic and asymptomatic distal junctional kyphosis (DJK). In this study the authors identified a DJK rate of 32.2%. Predictive models were created that can be used with high reliability to help distinguish between severe symptomatic DJK and mild asymptomatic DJK through the use of surgical factors, radiographic parameters, and patient variables.

METHODS

Patients with cervical deformity (CD) were stratified into asymptomatic and symptomatic DJK groups. Symptomatic: 1) DJK angle (DJKA) > 10° and either reoperation due to DJK or > 1 new-onset neurological sequela related to DJK; or 2) either a DJKA > 20° or ∆DJKA > 20°. Asymptomatic: ∆DJK > 10° in the absence of neurological sequelae. Stepwise logistic regressions were used to identify factors associated with these types of DJK. Decision tree analysis established cutoffs.

RESULTS

A total of 99 patients with CD were included, with 32.2% developing DJK (34.3% asymptomatic, 65.7% symptomatic). A total of 37.5% of asymptomatic patients received a reoperation versus 62.5% symptomatic patients. Multivariate analysis identified independent baseline factors for developing symptomatic DJK as follows: pelvic incidence (OR 1.02); preoperative cervical flexibility (OR 1.04); and combined approach (OR 6.2). Having abnormal hyperkyphosis in the thoracic spine, more so than abnormal cervical lordosis, was a factor for developing symptomatic disease when analyzed against asymptomatic patients (OR 1.2). Predictive modeling identified factors that were predictive of symptomatic versus no DJK, as follows: myelopathy (modified Japanese Orthopaedic Association score 12–14); combined approach; uppermost instrumented vertebra C3 or C4; preoperative hypermobility; and > 7 levels fused (area under the curve 0.89). A predictive model for symptomatic versus asymptomatic disease (area under the curve 0.85) included being frail, T1 slope minus cervical lordosis > 20°, and a pelvic incidence > 46.3°. Controlling for baseline deformity and disability, symptomatic patients had a greater cervical sagittal vertical axis (4–8 cm: 47.6% vs 27%) and were more malaligned according to their Scoliosis Research Society sagittal vertical axis measurement (OR 0.1) than patients without DJK at 1 year (all p < 0.05). Despite their symptomatology and higher reoperation rate, outcomes equilibrated in the symptomatic cohort at 1 year following revision.

CONCLUSIONS

Overall, 32.2% of patients with CD suffered from DJK. Symptomatic DJK can be predicted with high reliability. It can be further distinguished from asymptomatic occurrences by taking into account pelvic incidence and baseline cervicothoracic deformity severity.

In Brief

This study aimed to develop a predictive model distinguishing between symptomatic and asymptomatic distal junctional kyphosis. Symptomatic distal junctional kyphosis can be predicted by using combined baseline patient-specific factors and can be distinguished from asymptomatic occurrences by considering pelvic incidence and degree of cervicothoracic deformity. These clinical determinants can be used to reduce the risk of developing symptomatic and asymptomatic distal junctional kyphosis, and further help determine when junctional changes are compensatory or more inclined to have an adverse clinical impact.

Adult cervical deformity (CD) is a potentially debilitating disorder of the spine that is a result of radiographic malalignment of the cervical vertebral segments in the sagittal and/or coronal planes. Given that the cervical spine is a highly functional region, significant changes from normal alignment have been identified to significantly compromise a patient’s health-related quality of life (HRQOL).1–3 In more extreme forms, CD can predispose patients to a multitude of neurological manifestations, as well as abnormal breathing patterns, visual disturbance, and swallowing difficulty.4,5 Prevalence of CD has been thought to increase, partially related to an increase in spine surgeries taking place, coupled with an aging population. Equally relevant is the inherent risk associated with significant realignment in the cervical spine.6 Recent advancements in spinal realignment techniques and progress in our understanding of the compensatory mechanisms of the spinopelvic structure resulting from development of spinal deformities have enabled us to tackle more aggressive deformities. With these opposing themes occurring presently in CD surgery, together with value-based care becoming more sought after,7 efforts aimed at minimization of adverse outcomes are necessary.

Despite advancements in proposed alignment targets in efforts to reduce malcompensation and increase favorable short-term clinical results, the durability of CD remains a significant challenge.8,9 Distal junctional kyphosis (DJK) occurs at an approximate rate of 20% following CD surgery, and is one of the most highly considered concerns following cervical realignment, with clear connections to loss of alignment, neurological sequelae, and elevated revision rates.10 Different radiographic cutoffs have been proposed to characterize DJK, ranging from a deformity angle with 10° increase in kyphosis representing mild DJK to an increase > 20° representing severe DJK.11

Recently, several authors have identified a lack of clinical relevance in current literature in regard to outcomes and revision rates among patients with a classic threshold of 10° for DJK.11–13 With an increase in our understanding of preventive measures that can be applied to each patient individually, clinicians can better assess patients and modify surgical and perioperative strategies in order to reduce their risk of DJK development. The present study aimed to delineate independent risk factors associated with DJK and clinical consequence—differentiating severe 20° DJK associated with postoperative neurological sequelae/reoperation from its classic 10° radiographic counterpart. We further aimed to develop combinations of baseline factors that would determine with precision the occurrence of these adverse events.

Methods

Study Design

This study uses a database of consecutive, prospectively enrolled patients with CD who were > 18 years of age and whose records were obtained from 13 spine centers across the continental United States from 2013 to 2019. Through institutional review board approval and informed patient consent, the database was created including patients who met radiographic criteria for cervical kyphosis (C2–7 sagittal Cobb angle > 10°), cervical scoliosis (C2–7 coronal Cobb angle > 10°), C2–7 cervical sagittal vertical axis (cSVA) > 40 mm, or chin-brow vertical angle (CBVA) > 25°. The collected data that went into creating the database were routinely audited, monitored, and updated. Patients with active tumors, infection, fusion to pelvis, or deformity of neuromuscular etiology were excluded.

Data Collection

Patient comorbidity information14 and patient frailty were identified (not frail < 0.03, frail 0.3–0.5, severely frail > 0.5).15,16 HRQOL metrics were assessed using validated questionnaires such as the Neck Disability Index (NDI), numeric rating scales (NRSs) for neck and back pain, the EuroQol-5D health survey (EQ-5D), and the EQ-5D visual analog scale (VAS) score.1,17 Cervical myelopathy was also assessed via the modified Japanese Orthopaedic Association (mJOA) form.18

Radiographic data were identified through the use of long-cassette, full-standing anteroposterior and lateral radiographs, as well as cervical flexion/extension films. These radiographic parameters were analyzed using validated software (SpineView; ENSAM Laboratory of Biomechanics). Global and regional alignment parameters were assessed as follows: sagittal vertical axis (SVA; i.e., horizontal distance from C7 plumb line relative to the posterosuperior corner of S1); pelvic tilt (PT); pelvic incidence (PI); thoracic kyphosis (TK); lumbar lordosis (LL); cervical lordosis (CL); cSVA (i.e., the angle between the line drawn from the center of the sacral endplate to the center of the femoral head axis and the line perpendicular to the sacral endplate); and cervical flexibility as measured by extension at C2–7 minus flexion at C2–7. Patients were also identified for their Ames CD classification for the following modifiers: C2–7 (i.e., cSVA), CBVA (i.e., horizontal gaze), TS−CL (T1 slope minus CL), and mJOA.19 The McGregor slope was used as a surrogate for CBVA when this measurement was not available.20

Assessment of DJK Groups

DJK was defined radiographically via the Cobb angle method as > 10° kyphosis between the superior endplate of the lowest instrumented vertebra (LIV) and the inferior endplate of the second distal vertebra (i.e., LIV − 2), in addition to a pre- to postoperative change in DJK angle (DJKA) > 10°. Symptomatic DJK was defined as patients having 1) DJKA > 10° and either reoperation due to DJK or 1 or more new-onset neurological sequelae related to DJK (including spinal cord deficit, gait disturbance, hyperreflexia, and lower-limb spasticity); or 2) either a DJKA > 20° or ∆DJKA > 20°.21 Asymptomatic DJK was defined as pre- to postoperative change in DJK > 10° in the absence of neurological sequelae.

Statistical Analysis

Descriptive analyses summarized patient-related demographic, surgical, and radiographic variables. ANOVA explored differences in patient-reported outcome measures across DJK groups at baseline to 1-year follow-up. Predictive models were created to identify variables predictive of developing asymptomatic and symptomatic disease through using logistic regressions in univariate and multivariate manners as follows. Univariate analyses displayed variables that were statistically significant and clinically meaningful. If variables exhibited a p value < 0.10 and were clinically justifiable, they were entered into the multivariable model. Stepwise forward regression performed using the Akaike information criterion was used to select which variable should be included in the final predictive model of DJK occurrence. The performances of the predictive models were assessed via the average area under the curve (AUC), sensitivity, and specificity for outcome measures. Decision tree analysis identified cutoffs for continuous variables in the predictive models. A p value < 0.05 was considered statistically significant.

Results

Baseline Presentation

A total of 167 consecutive patients with CD were included in the analysis, with 99 patients having complete 1-year postoperative follow-up. The patient population was 66.7% female, with a mean age of 61.4 ± 10.1 years, and a mean BMI of 28.5 kg/m2. Five patients had either osteopenia or osteoporosis. Of these patients, 50.5% underwent a decompression and 85.9% underwent an osteotomy. The average number of levels fused was 7.4 ± 3.7. A total of 47.5% underwent a posterior approach, 18.2% underwent an anterior approach, and 34.3% underwent a combined approach (Table 1). The most common uppermost instrumented vertebra (UIV) was C2 (minimum C1, maximum C6), and the most common LIV was T9 (minimum C6, maximum L2).

TABLE 1.

Overall baseline demographic and surgical data of the included CD cohort (n = 99)

Total CohortSymptomatic (n = 21)Asymptomatic (n = 11)p Value
Demographics
 Age (yrs)61.4 ± 10.159.263.70.22
 BMI (kg/m2)28.5 ± 7.324.128.50.04
 Sex (% female)66.7%81%54.5%0.11
Surgical factors
 Levels fused7.4 ± 3.749.77.50.19
 Posterior-only approach47.5%66.7%54.5%0.5
 Anterior-only approach18.2%9.5%18.2%0.48
 Combined approach34.3%23.3%27.3%0.8
 Osteotomy85.9%90.5%90.9%0.98
 UIV (mode)C2 (48.5%)2.83.70.19
 LIV (mode)T9 (22.2%)12.511.20.49

Age, BMI, and number of levels fused in the total cohort are expressed as the mean ± SD. Symptomatic and asymptomatic UIV and LIV are expressed as the mean level. Boldface type indicates statistical significance.

Radiographic Alignment

These patients presented at baseline with a mean PT = 19.2°, PI-LL mismatch (PI-LL) = −0.01, TK = −38.4°, C2–7 SVA = 45.3 mm, TS−CL = 37.2°, C7–S1 SVA = −4.7 mm, and a McGregor slope = 4.2°. By Ames criteria at presentation, for cSVA: 0 = 52.6%, 1 = 47.4%; for horizontal gaze: 0 = 26.9%, 1 = 47.4%, 2 = 25.6%; for T1 slope: 0 = 8.4%, 1 = 6.3%, 2 = 85.3%; and for mJOA: 0 = 8.9%, 1 = 35.6%, 2 = 35.6%, 3 = 17.1%.

DJK Occurrence and Differences in Presenting Characteristics

Overall, 32.2% of patients developed DJK as defined by DJKA > 10° (21.2% at 6 weeks, 33.3% at 3 months, 3% at 6 months, 27.3% at 1 year, and 15.2% at 2 years). Patients with DJK were identified to have a lower baseline BMI than those who did not develop postoperative DJK (25.5 kg/m2 vs 29.5 kg/m2; p < 0.05). Surgically, patients with DJK had a lower estimated blood loss (314 mL vs 564.4 mL; p = 0.04). Of those who developed DJK, 34.3% were asymptomatic (n = 11) and 65.7% were symptomatic (n = 21). Asymptomatic patients had a higher baseline BMI than symptomatic patients (28.5 kg/m2 vs 24.1 kg/m2; p = 0.04; Table 1). Symptomatic patients had a greater reoperation rate than the asymptomatic group (62.5% vs 34.3%; p < 0.05) and a higher McGregor slope, identified as > 21° (42.9% vs 0%; p = 0.03). These patients did not differ in radiographic baseline deformity or HRQOL information (Table 2).

TABLE 2.

HRQOL and alignment for asymptomatic and symptomatic DJK at baseline

Total CohortSymptomatic (n = 21)Asymptomatic (n = 11)p Value
Baseline HRQOL scores
 NDI53.653.60.67
 NRS score for back pain4.94.90.86
 NRS score for neck pain7.26.150.50
 EQ-5D0.720.720.77
 mJOA12.414.00.136
Baseline alignment
 SS (°)36.035.80.96
 PI (°)50.854.60.35
 PT (°)14.818.70.42
 PI-LL (°)−7.6−0.160.35
 L1–S1 (°)5358.40.47
 T10–L2 (°)−18.5−7.50.01
 CL (°)48.157.90.34
 TS–CL (°)41.0533.80.43
 T12–S1 (°)48.155.90.26
 cSVA (mm)43.947.20.68
 C0–C2 sagittal Cobb angle (°)35.528.80.29
 McGregor slope (°)8.64.10.49

Boldface type indicates statistical significance.

DJK Effect on Postoperative Alignment and Outcomes

DJK was not identified to have a significant impact on 1-year HRQOL outcomes; however, those who developed DJK had greater C2–7 plumb line (47.9° vs 36.8°), C2–T3 (85.6° vs 71.1°), and C2–SS (sacral slope) (30.2° vs 24.1°; all p < 0.05) values. Symptomatic patients reported worse back pain (NRS score 5.8 vs 3.2; p = 0.04; Table 3) and had greater improvement from baseline to 1 year postoperatively for NDI than asymptomatic patients (p = 0.02). Radiographically, symptomatic patients had an increase in their TK from baseline (−43.9° to −49.1°), which led to significant decreases in the thoracolumbar region (T10–L2: −9.0° to −18.5°; p = 0.023) and in the cervicothoracic region (C2–T3: −19.2° to −3.5°; p = 0.04) in order to properly compensate. In contrast, asymptomatic patients show minimal change in their T4–12 kyphosis (−43.6° to −44.2°) and therefore only experienced reciprocal decrease in their C2–7 plumb line alignment (33.8° to 26.6°; p = 0.01).

TABLE 3.

One-year HRQOL scores

Total CohortSymptomatic (n = 21)Asymptomatic (n = 11)p Value
1-yr HRQOL scores
 NDI30.940.10.40
 NRS score for back pain5.83.270.04
 NRS score for neck pain5.34.090.32
 EQ-5D0.740.810.09
 mJOA score13.314.670.38

Boldface type indicates statistical significance.

Predictive Model for the Development of Symptomatic DJK

Multivariate analysis indicated that most baseline demographic factors did not show a relationship when predicting symptomatic against no DJK, except for patient frailty (OR 34.8, 95% CI 1.4–21890.9; p = 0.28). HRQOL scores at baseline such as mJOA (OR 0.9, 95% CI 0.82–1.02; p = 0.13) and NDI (OR 0.9, 95% CI 0.94–1.03; p = 0.68) were identified in the multivariate analysis as being associated with development of symptomatic DJK, as were levels fused (OR 0.8, 95% CI 0.64–1.05; p = 0.12); UIV (OR 1.5, 95% CI 0.93–2.7; p = 0.08); and receiving a combined approach (OR 6.5, 95% CI 1.4–29.2; p = 0.01). Radiographic variables at baseline were the most numerous predictors of DJK incidence—the majority of these predictors pertained to structures in the cervical region, with cervical flexibility and location of primary deformity having the greatest effect (Table 4). The predictive model for developing symptomatic DJK had high accuracy (AUC 88.2%) using the following factors: combined surgical approach; frail presentation; baseline moderate mJOA score by Ames criteria (12–14); UIV at or cranial to C3 relative to the cervicothoracic junction; number of levels fused > 7; and preoperative hypermobility (extension minus flexion > 9°).

TABLE 4.

Formal model predicting symptomatic DJK versus no DJK

CutoffORLower CIUpper CIp Value
Predictive model factors
 InterceptNA0.0090.000.190.003
 Combined approachNA4.91.318.10.016
 Baseline frailtyNA60.60.8940950.05
 Baseline mJOA score12–140.920.831.020.13
 UIVC31.61.022.50.04
 No. of levels fused>70.840.681.040.11
 Cervical hypermobilityNA1.031.0031.070.03

NA = not applicable.

AUC 88.2%. Boldface type indicates statistical significance.

Predictive Model for Symptomatic Versus Asymptomatic DJK

Baseline demographic factors did not show a relationship when predicting symptomatic versus asymptomatic DJK. Clinically, the LIV of the index surgery was selected by our multivariate analysis predicting symptomatic DJK (OR 0.90, 95% CI 0.6–1.2; p = 0.52). Radiographic variables at baseline or within 3 months postoperatively were the most numerous in the multivariate analysis—their effect size in decreasing magnitude was as follows: primary driver thoracic (OR 1.15, 95% CI 0.01–1.15; p = 0.95); 3-month C2–T3 ≥ 1.7 (OR 1.045, 95% CI 0.9–1.19; p = 0.53); baseline S1-PI ≥ 54.1° (OR 1.04, 95% CI 0.98–1.09; p = 0.13); and baseline TS−CL ≥ 51.6° (OR 0.96, 95% CI 0.87–1.06; p = 0.49). A predictive model for symptomatic versus asymptomatic patients yielded an AUC of 85% and included being frail, having a TS−CL > 20°, and a PI > 46.3° (Table 5). Controlling for baseline deformity and disability, symptomatic patients had greater cSVA (4–8 cm: 47.6% vs 27%) and were more malaligned according to their Scoliosis Research Society (SRS)–SVA (0.1 [range 0.02–0.76]) than patients without DJK at 1 year (all p < 0.05). The same trend was seen for these parameters at 3 months (p < 0.05).

TABLE 5.

Formal model predicting symptomatic DJK versus asymptomatic DJK

Cutoff ORLower CIUpper CIp Value
Predictive model factors
 InterceptNA0.0160.001.50.077
 Baseline frailNA3.0 × 1060.432.1 × 10110.06
 Baseline TS–CL>20°0.950.891.010.12
 Baseline S1-PI>46.3°1.040.991.090.07

AUC 85.0%.

Radiographic and Clinical Outcomes After Treatment

After receiving treatment for their DJK, symptomatic patients significantly improved in their SVA C7–S1 alignment (−11.07 to 35.5 mm; p < 0.05). After treatment, symptomatic patients had significantly lower NDI scores (51.27 to 13.27; p < 0.05), yet they trended toward an increase in NRS–back pain (3.3 to 4.7; p = 0.061; Fig. 1). Likewise, asymptomatic patients significantly decreased their NDI scores (45.8 to 12.5) as well as their NRS–neck pain scores (4.6 to 3.2; all p < 0.05; Fig. 2). However, these patients had significantly increased their NRS–back pain scores (3.6 to 4.8; p = 0.02).

FIG. 1.
FIG. 1.

A: Baseline radiograph obtained in a 57-year-old woman who presented with a TK of −37.3°. The patient had been diagnosed with diabetes and osteoporosis at that time. Concomitantly, the patient suffered from neurological bowel, bladder, gait, and hand issues. The patient underwent a posterior cervical fusion that consisted of 16 levels (UIV C2, LIV T11) and had a baseline DJKA of −3.2°. B: Radiographs obtained 3 months postoperatively. By 3 months postoperatively, the patient developed symptomatic DJK and had an increase in TK of −70.5°. From baseline to 1 year, the patient had worsened in her NRS–back pain scores by 2 points (from 5 to 7) and had a worse EQ-5D VAS score (from 90 to 48).

FIG. 2.
FIG. 2.

A: Baseline radiograph obtained in a 76-year-old woman who presented with a TK −59.1° and with moderate myelopathy. The patient underwent a posterior cervical fusion that consisted of 13 levels (UIV C2, LIV T8) and had a baseline DJKA of −21.6°. B: Radiograph obtained 1 year postoperatively. By 1 year postoperatively, the patient developed asymptomatic DJK and had an increase in TK of −63.5°. From baseline to 1 year, the patient had improvement in her NRS–neck pain (from 6 to 4), EQ-5D (from 0.832 to 0.80), and EQ-5D VAS (from 50 to 80) scores.

Discussion

The advancements brought on by increased research and development of novel techniques/technologies have allowed surgeons to treat complex adult CDs. However, the postoperative development of junctional kyphosis has increased with modern instrumentation, including pedicle screw constructs and aggressive realignments.22,23 In many cases, DJK may be associated with an observed loss in regional or global sagittal alignment that requires surgical correction, but others may remain clinically asymptomatic despite the degree of kyphosis.24 With most of the literature focusing on adult spinal deformity and identifying risk factors, etiologies, and types of kyphosis in this patient population, there has been a lack of literature distinguishing these patients with asymptomatic and symptomatic cervical DJK as well as the specific factors predictive of either occurrence.24,25 Our study identified parameters that can be used with high reliability in order to preoperatively predict the occurrence of symptomatic DJK and further distinguish it from asymptomatic DJK with consideration of relevant baseline factors including severity of cervicothoracic deformity and PI.

The current study created a predictive model for severe clinically relevant DJK and a model that provided further distinction of these symptomatic cases from mild asymptomatic episodes, with the overall incidence rate of DJK being 32.2% for patients with surgically treatable CD. This rate is slightly higher than that reported by Passias et al.,26 which found a DJK incidence of 23.8% over 1 year in a population of 101 patients with CD. Of those who developed DJK, we identified 65.7% who had at least one or more documented postoperative neurological sequelae either not present preoperatively or neurologically deteriorating postoperatively, in conjunction with a curve of 20° (symptomatic DJK), whereas the rest of the patients with 10° DJK (34.3%) possessed neither attribute and were considered asymptomatic. This prevalence identified for symptomatic patients is supported by Protopsaltis et al.; they found neuromuscular etiologies such as cervical myelopathy, Parkinson disease, or other neuromuscular diseases present in 76% of patients with junctional kyphosis.12 Other such studies have identified that there is a correlation between neurological comorbidities and development of DJK, some of which state that the neurological component worsens a patient’s DJK or is more of a reflection of those with less neurological reserve.26

The most radiographically relevant cutoff point identified for development of symptomatic DJK was having a hypermobile (> 11°) cervical spine at presentation, and further distinctions from mild cases were TS−CL > 20° and S1-PI > 46.3°. The T1 slope has been previously identified to be a useful parameter for predicting DJK, but has been associated with a greater degree of deformity than what was identified in our cohort (> 36.4°).27 In addition to these radiographic parameters, surgical variables that were identified to predict symptomatic occurrence were as follows: receiving a combined approach, having a UIV of C3–4, and receiving > 7 levels fused. Kim and Iyer identified that receiving a combined approach increased a patient’s risk of proximal junctional kyphosis (PJK) development by 3 times, whereas in our cohort a combined approach doubled these odds of DJK development, with an OR of 6.2 (p = 0.01).28 The choice of UIV placement and number of levels fused can have further biomechanical consequences that may lead to development of DJK, given that it has been previously shown to affect PJK development. A study done by Bridwell et al. found that for cases of severe PJK, having shorter constructs (median of 8 levels fused) and a UIV in the thoracic spine (T8 and lower) significantly increased the risk of PJK.29 In the current study, we identified through our univariate analysis that number of levels fused played a role in predicting symptomatic DJK. Once we formalized our predictive model, we saw that having > 7 levels fused increased a patient’s odds of developing symptomatic DJK by 0.84 (p = 0.11), which is a reflection of how longer, rigid constructs affect the spine’s biomechanics by creating additional junctional strain on adjacent segments.

Demographically, a patient’s age, BMI, sex, Charlson Comorbidity Index, and ambulatory status did not have a significant effect on the development of DJK. Even though osteoporosis is commonly associated with poor bone quality and is often reported as a risk factor for development of DJK,5 in the current study we only identified 5 patients having a comorbidity of osteoporosis, and all were symptomatic. As a result, this study was not able to reach an accurate conclusion about the effect that osteoporosis has on the development of DJK. Additionally, DJK development was not found to significantly alter HRQOL outcomes. We ascribe this to the low power of the sample as well as the comparison of patients without DJK to a combined cohort of patients with asymptomatic and symptomatic DJK.

Limitations of the present study include a relatively small cohort size of patients with DJK when stratifying patients by severe symptomatic and mild asymptomatic. In addition, the CD cohort included in our analysis presented with severe baseline sagittal malalignment and were elderly. This may limit the overall generalizability of our findings for a clinically relevant DJK, given that younger patients with less deformity may be less prone to neurological sequelae, more resistant to pain, and more able to compensate following correction. In addition, we could not imply causation of the neurological sequelae due to the DJK, which represents a broader limitation of our retrospective analysis. Still, the temporal association between each patient’s neurological sequelae and their DJK, coupled with the multicenter, prospective nature of our study, allows for a compelling theme on how differentiating between clinically relevant and asymptomatic DJK can prove useful during preoperative assessment. Last, there may be selection bias due to exclusion criteria leaving out patients with incomplete or improperly reported HRQOL data.

Conclusions

In a surgical cohort of patients with CD, we found an overall 32% incidence of DJK. Severe symptomatic DJK can be predicted with high reliability by using combined determinants of baseline spinal cord dysfunction, mobility, frailty, and surgical factors including end levels, number of levels fused, and use of a combined approach. It can be further distinguished from asymptomatic occurrences by taking into account PI and baseline severity of cervicothoracic deformity.

Disclosures

Dr. Passias—Allosource: other financial or material support; Cervical Scoliosis Research Society: research support; Globus Medical: paid presenter or speaker; Medicrea: paid consultant; Royal Biologics: paid consultant; SpineWave: paid consultant; Terumo: paid consultant; Zimmer: paid presenter or speaker. Mr. R. Lafage—Nemaris: stock or stock options. Dr. V. Lafage—DePuy, a Johnson & Johnson Company: paid presenter or speaker; European Spine Journal: editorial or governing board; Globus Medical: paid consultant; International Spine Study Group: board or committee member; NuVasive: IP royalties; SRS: board or committee member; The Permanente Medical Group: paid presenter or speaker. Dr. Protopsaltis—Altus: IP royalties; Globus Medical: paid consultant; Medicrea: paid consultant; NuVasive: paid consultant; Spine Align: stock or stock options; Stryker: paid consultant; Torus Medical: stock or stock options. Dr. Kim—AAOS: board or committee member; Alphatec Spine: paid consultant; AO Spine: board or committee member; Cervical Spine Research Society: board or committee member; HSS Journal: editorial or governing board; Asian Spine Journal: editorial or governing board; ISSG Foundation: research support; K2M: IP royalties; SRS: board or committee member; Zimmer: IP royalties. Dr. Eastlack—Aesculap/B. Braun: paid consultant; Alphatec Spine: stock or stock options; Baxter: paid consultant; Biedermann-Motech: paid consultant; Carevature: paid consultant, stock or stock options; Globus Medical: IP royalties; Invuity: stock or stock options; Medtronic: paid consultant; Nocimed: stock or stock options; NuVasive: IP royalties, paid consultant, research support, stock or stock options; Radius: paid presenter or speaker; San Diego Spine Foundation: board or committee member; SRS: board or committee member; SeaSpine: IP royalties, paid consultant, stock or stock options; SI Bone: IP royalties, paid consultant; Society of Lateral Access Surgery: board or committee member; Spine Innovations: stock or stock options; Stryker: paid consultant. Dr. Klineberg—AO Spine: paid presenter or speaker, research support; DePuy, a Johnson & Johnson Company: paid consultant; Medicrea: paid consultant; Medtronic: paid consultant; Stryker: paid consultant. Dr. Hart—American Orthopaedic Association: board or committee member; Cervical Spine Research Society: board or committee member; DePuy, a Johnson & Johnson Company: IP royalties, paid consultant, paid presenter or speaker; Globus Medical: IP royalties, paid consultant, paid presenter or speaker; ISSG: board or committee member; ISSLS Textbook of the Lumbar Spine: editorial or governing board; Medtronic: paid consultant, paid presenter or speaker; North American Spine Society: board or committee member; Orthofix, Inc.: paid consultant, paid presenter or speaker; SRS: board or committee member; SeaSpine: IP royalties; Spine Connect: stock or stock options; Western Orthopaedic Association: board or committee member. Dr. Burton—Bioventus: research support; DePuy, a Johnson & Johnson Company: IP royalties, paid consultant, research support; Pfizer: research support; Progenerative Medical: stock or stock options; SRS: board or committee member; Spine Deformity: editorial or governing board. Dr. Bess—Allosource: paid consultant, research support; Biomet: research support; DePuy, a Johnson & Johnson Company: paid consultant, research support; EOS: research support; Globus Medical: research support; K2 Medical: IP royalties, paid consultant, paid presenter or speaker, research support; Medtronic Sofamor Danek: research support; North American Spine Society: board or committee member; NuVasive: IP royalties, research support; Orthofix, Inc.: research support; SRS: board or committee member; Stryker: IP royalties, paid presenter or speaker. Dr. Schwab—DePuy, a Johnson & Johnson Company: research support; Globus Medical: paid consultant, paid presenter or speaker; K2M: IP royalties, paid consultant, paid presenter or speaker; Medicrea: paid consultant; Medtronic: paid consultant; Medtronic Sofamor Danek: IP royalties, paid presenter or speaker; NuVasive: research support; SRS: board or committee member; Spine Deformity: editorial or governing board; Stryker: research support; ISSG, vice president: board or committee member; Zimmer: IP royalties, paid consultant, paid presenter or speaker. Dr. Shaffrey—AANS: board or committee member; Cervical Spine Research Society: board or committee member; DePuy, a Johnson & Johnson Company: paid presenter or speaker, research support; Globus Medical: research support; Medtronic: other financial or material support, paid consultant; Medtronic Sofamor Danek: IP royalties, paid presenter or speaker, research support; Neurosurgery RRC: board or committee member; NuVasive: IP royalties, paid consultant, paid presenter or speaker, research support, stock or stock options; SI Bone: IP royalties; Spinal Deformity: editorial or governing board; Spine: editorial or governing board. Dr. Smith—Alphatec Spine: stock or stock options; Carlsmed: paid consultant; Cerapedics: paid consultant; DePuy: research support; DePuy, a Johnson & Johnson Company: paid consultant; Journal of Neurosurgery: Spine: editorial or governing board; Neurosurgery: editorial or governing board; NuVasive: IP royalties, paid consultant, research support; Operative Neurosurgery: editorial or governing board; SRS: board or committee member; Spine Deformity: editorial or governing board; Stryker: paid consultant; Thieme: publishing royalties, financial or material support; Zimmer: IP royalties, paid consultant. Dr. Ames—Biomet Spine: IP royalties; DePuy, a Johnson & Johnson Company: IP royalties, paid consultant, research support; Global Spine Analytics, director: other financial or material support; ISSG: research support; ISSG, executive committee: other financial or material support; K2M: IP royalties, paid consultant; Medicrea: IP royalties, paid consultant; Medtronic: paid consultant; Next Orthosurgical: IP royalties; NuVasive: IP royalties; Operative Neurosurgery, editorial board: other financial or material support; SRS, grant funding: other financial or material support; Stryker: IP royalties; Titan Spine: research support.

Author Contributions

Conception and design: Passias, Naessig, R Lafage, V Lafage, Diebo, Protopsaltis, Kim, Eastlack, Soroceanu, Klineberg, Hart, Burton, Bess, Schwab, Shaffrey, Smith, Ames. Acquisition of data: Passias, Naessig, R Lafage, V Lafage, Line, Protopsaltis, Kim, Eastlack, Soroceanu, Klineberg, Hart, Burton, Bess, Schwab, Shaffrey, Smith, Ames. Analysis and interpretation of data: Passias, Naessig, Kummer, Passfall, Diebo. Drafting the article: Naessig, Kummer, Passfall. Critically revising the article: all authors. Reviewed submitted version of manuscript: Naessig, Kummer, Passfall, R Lafage, V Lafage, Line, Diebo, Protopsaltis, Kim, Eastlack, Soroceanu, Klineberg, Hart, Burton, Bess, Schwab, Shaffrey, Smith, Ames. Approved the final version of the manuscript on behalf of all authors: Passias. Statistical analysis: Passias, Naessig. Administrative/technical/material support: Passias, R Lafage, V Lafage, Line. Study supervision: Passias, V Lafage.

Supplemental Information

Previous Presentations

North American Spine Society Conference (NASS 2020; podium), San Diego, CA; and the SRS 55th Annual Meeting (SRS 2020; poster), Phoenix, AZ.

References

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    Smith JS, Line B, Bess S, Shaffrey CI, Kim HJ, Mundis G, et al. The Health Impact of Adult Cervical Deformity in Patients Presenting for Surgical Treatment: Comparison to United States Population Norms and Chronic Disease States Based on the EuroQuol-5 Dimensions Questionnaire. Neurosurgery. 2017;80(5):716725.

    • Crossref
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    Passias PG, Soroceanu A, Smith J, Boniello A, Yang S, Scheer JK, et al. Postoperative cervical deformity in 215 thoracolumbar patients with adult spinal deformity: prevalence, risk factors, and impact on patient-reported outcome and satisfaction at 2-year follow-up. Spine (Phila Pa 1976).2015;40(5):283291.

    • Crossref
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  • 3

    Bogduk N. Functional anatomy of the spine. Handb Clin Neurol. 2016;136(675):688.

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    Uchida K, Nakajima H, Sato R, Yayama T, Mwaka ES, Kobayashi S, Baba H. Cervical spondylotic myelopathy associated with kyphosis or sagittal sigmoid alignment: outcome after anterior or posterior decompression. J Neurosurg Spine. 2009;11(5):521528.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5

    Caruso L, Barone G, Farneti A, Caraffa A. Pedicle subtraction osteotomy for the treatment of chin-on-chest deformity in a post-radiotherapy dropped head syndrome: a case report and review of literature. Eur Spine J. 2014;23(suppl 6):634643.

    • Crossref
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    • Export Citation
  • 6

    Patel PD, Arutyunyan G, Plusch K, Vaccaro A Jr, Vaccaro AR. A review of cervical spine alignment in the normal and degenerative spine. J Spine Surg. 2020;6(1):106123.

    • Crossref
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    • Search Google Scholar
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  • 7

    Hills JM, Weisenthal B, Sivaganesan A, Bydon M, Archer KR, Devin CJ. Value based spine care: paying for outcomes, not volume. Semin Spine Surg. 2019;31(1):1219.

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    Lafage R, Schwab F, Glassman S, Bess S, Harris B, Sheer J, et al. Age-adjusted alignment goals have the potential to reduce PJK. Spine (Phila Pa 1976).2017;42(17):12751282.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9

    Schwab FJ, Lafage R, Glassman SD, Bess S, Harris B, Sheer J, et al. Age-adjusted alignment goals have the potential to reduce PJK. Spine (Phila Pa 1976).2017;42(17):12751282.

    • Crossref
    • Search Google Scholar
    • Export Citation
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    Scheer JK, Fakurnejad S, Lau D, Daubs MD, Coe JD, Paonessa KJ, et al. Results of the 2014 SRS Survey on PJK/PJF: a report on variation of select SRS member practice patterns, treatment indications, and opinions on classification development. Spine (Phila Pa 1976).2015;40(11):829840.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11

    Lowe TG, Lenke L, Betz R, Newton P, Clements D, Haher T, et al. Distal junctional kyphosis of adolescent idiopathic thoracic curves following anterior or posterior instrumented fusion: incidence, risk factors, and prevention. Spine (Phila Pa 1976).2006;31(3):299302.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12

    Protopsaltis TS, Stekas N, Lafage R, Smith JS, Soroceaunu A, Sciubba DM, et al. Impact of adult deformity correction: 261. Can we define clinically relevant DJK in cervical deformity surgery? Spine J. 2018;18(8 Suppl):S129S130.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13

    Protopsaltis TS, Ramchandran S, Kim HJ, et al. Analysis of early distal junctional kyphosis (DJK) after cervical deformity correction. Spine J. 2016;16(10):S355S356.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14

    Charlson M, Szatrowski TP, Peterson J, Gold J. Validation of a combined comorbidity index. J Clin Epidemiol. 1994;47(11):12451251.

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    Miller EK, Neuman BJ, Jain A, Daniels AH, Ailon T, Sciubba DM, et al. An assessment of frailty as a tool for risk stratification in adult spinal deformity surgery. Neurosurg Focus. 2017;43(6):E3.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Searle SD, Mitnitski A, Gahbauer EA, Gill TM, Rockwood K. A standard procedure for creating a frailty index. BMC Geriatr. 2008;8 24.

  • 17

    Vernon H, Mior S. The Neck Disability Index: a study of reliability and validity. J Manipulative Physiol Ther. 1991;14(7):409415.

  • 18

    Tetreault L, Kopjar B, Nouri A, Arnold P, Barbagallo G, Bartels R, et al. The modified Japanese Orthopaedic Association scale: establishing criteria for mild, moderate and severe impairment in patients with degenerative cervical myelopathy. Eur Spine J. 2017;26(1):7884.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 19

    Smith JS, Eastlack RK, Blaskiewicz DJ, Shaffrey CI, Schwab FJ, Bess S, et al. Reliability assessment of a novel cervical deformity classification system. In: International Meeting on Advanced Spine Techniques (IMAST). SRS;2014.Accessed September 30, 2021. https://www.srs.org/UserFiles/file/meetings/imast2014/IMAST14-Final-4web3.pdf

    • Search Google Scholar
    • Export Citation
  • 20

    Moses MJ, Tishelman JC, Zhou PL, Moon JY, Beaubrun BM, Buckland AJ, Protopsaltis TS. McGregor’s slope and slope of line of sight: two surrogate markers for chin-brow vertical angle in the setting of cervical spine pathology. Spine J. 2019;19(9):15121517.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 21

    Ayres EW, Protopsaltis TS, Lafage R, et al. 298. Predicting the magnitude of distal junctional kyphosis following cervical deformity correction. Spine J. 2019;19(9):S145.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 22

    Blondel B, Lafage V, Farcy JPP, Schwab F, Bollini G, Jouve JLL. Influence of screw type on initial coronal and sagittal radiological correction with hybrid constructs in adolescent idiopathic scoliosis. Correction priorities. Orthop Traumatol Surg Res. 2012;98(8):873878.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23

    Arbash MA, Parambathkandi AM, Baco AM, Alhammoud A. Impact of screw type on kyphotic deformity correction after spine fracture fixation: cannulated versus solid pedicle screw. Asian Spine J. 2018;12(6):10531059.

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    Lundine K, Turner P, Johnson M. Thoracic hyperkyphosis: assessment of the distal fusion level. Global Spine J. 2012;2(2):6570.

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    Liabaud B, Lafage R, Hart RA, Schwab FJ, Smith JS, Kim HJ, et al. Proximal junctional kyphosis (PJK) can be predicted following adult spinal deformity (ASD) surgery: models based on regional alignment changes within the fusion area. Spine J. 2016;16(10)(suppl):S132.

    • Crossref
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    Passias PG, Vasquez-Montes D, Poorman GW, Protopsaltis T, Horn SR, Bortz CA, et al. Predictive model for distal junctional kyphosis after cervical deformity surgery. Spine J. 2018;18(12):21872194.

    • Crossref
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    Passias PG, Horn SR, Oh C, Lafage R, Lafage V, Smith JS, et al. Predicting the occurrence of postoperative distal junctional kyphosis in cervical deformity patients. Neurosurgery. 2020;86(1):E38E46.

    • Crossref
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    Kim HJ, Iyer S. Proximal junctional kyphosis. J Am Acad Orthop Surg. 2016;24(5):318326.

  • 29

    Bridwell KH, Lenke LG, Cho SK, Pahys JM, Zebala LP, Dorward IG, et al. Proximal junctional kyphosis in primary adult deformity surgery: evaluation of 20 degrees as a critical angle. Neurosurgery. 2013;72(6):899906.

    • Crossref
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  • Collapse
  • Expand

Schematic image of the spine (L1–pelvis) instrumented with transforaminal (upper left), anterior (center left), and lateral (lower left) lumbar interbody fixation devices as a standalone cage (upper right) and with supplemental posterior fixation (lower right) at the L4–5 level. © Margaret Sten, published with permission. See the article by Kiapour et al. (pp 928–936).

  • View in gallery
    FIG. 1.

    A: Baseline radiograph obtained in a 57-year-old woman who presented with a TK of −37.3°. The patient had been diagnosed with diabetes and osteoporosis at that time. Concomitantly, the patient suffered from neurological bowel, bladder, gait, and hand issues. The patient underwent a posterior cervical fusion that consisted of 16 levels (UIV C2, LIV T11) and had a baseline DJKA of −3.2°. B: Radiographs obtained 3 months postoperatively. By 3 months postoperatively, the patient developed symptomatic DJK and had an increase in TK of −70.5°. From baseline to 1 year, the patient had worsened in her NRS–back pain scores by 2 points (from 5 to 7) and had a worse EQ-5D VAS score (from 90 to 48).

  • View in gallery
    FIG. 2.

    A: Baseline radiograph obtained in a 76-year-old woman who presented with a TK −59.1° and with moderate myelopathy. The patient underwent a posterior cervical fusion that consisted of 13 levels (UIV C2, LIV T8) and had a baseline DJKA of −21.6°. B: Radiograph obtained 1 year postoperatively. By 1 year postoperatively, the patient developed asymptomatic DJK and had an increase in TK of −63.5°. From baseline to 1 year, the patient had improvement in her NRS–neck pain (from 6 to 4), EQ-5D (from 0.832 to 0.80), and EQ-5D VAS (from 50 to 80) scores.

  • 1

    Smith JS, Line B, Bess S, Shaffrey CI, Kim HJ, Mundis G, et al. The Health Impact of Adult Cervical Deformity in Patients Presenting for Surgical Treatment: Comparison to United States Population Norms and Chronic Disease States Based on the EuroQuol-5 Dimensions Questionnaire. Neurosurgery. 2017;80(5):716725.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Passias PG, Soroceanu A, Smith J, Boniello A, Yang S, Scheer JK, et al. Postoperative cervical deformity in 215 thoracolumbar patients with adult spinal deformity: prevalence, risk factors, and impact on patient-reported outcome and satisfaction at 2-year follow-up. Spine (Phila Pa 1976).2015;40(5):283291.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3

    Bogduk N. Functional anatomy of the spine. Handb Clin Neurol. 2016;136(675):688.

  • 4

    Uchida K, Nakajima H, Sato R, Yayama T, Mwaka ES, Kobayashi S, Baba H. Cervical spondylotic myelopathy associated with kyphosis or sagittal sigmoid alignment: outcome after anterior or posterior decompression. J Neurosurg Spine. 2009;11(5):521528.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5

    Caruso L, Barone G, Farneti A, Caraffa A. Pedicle subtraction osteotomy for the treatment of chin-on-chest deformity in a post-radiotherapy dropped head syndrome: a case report and review of literature. Eur Spine J. 2014;23(suppl 6):634643.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6

    Patel PD, Arutyunyan G, Plusch K, Vaccaro A Jr, Vaccaro AR. A review of cervical spine alignment in the normal and degenerative spine. J Spine Surg. 2020;6(1):106123.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7

    Hills JM, Weisenthal B, Sivaganesan A, Bydon M, Archer KR, Devin CJ. Value based spine care: paying for outcomes, not volume. Semin Spine Surg. 2019;31(1):1219.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8

    Lafage R, Schwab F, Glassman S, Bess S, Harris B, Sheer J, et al. Age-adjusted alignment goals have the potential to reduce PJK. Spine (Phila Pa 1976).2017;42(17):12751282.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9

    Schwab FJ, Lafage R, Glassman SD, Bess S, Harris B, Sheer J, et al. Age-adjusted alignment goals have the potential to reduce PJK. Spine (Phila Pa 1976).2017;42(17):12751282.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10

    Scheer JK, Fakurnejad S, Lau D, Daubs MD, Coe JD, Paonessa KJ, et al. Results of the 2014 SRS Survey on PJK/PJF: a report on variation of select SRS member practice patterns, treatment indications, and opinions on classification development. Spine (Phila Pa 1976).2015;40(11):829840.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11

    Lowe TG, Lenke L, Betz R, Newton P, Clements D, Haher T, et al. Distal junctional kyphosis of adolescent idiopathic thoracic curves following anterior or posterior instrumented fusion: incidence, risk factors, and prevention. Spine (Phila Pa 1976).2006;31(3):299302.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12

    Protopsaltis TS, Stekas N, Lafage R, Smith JS, Soroceaunu A, Sciubba DM, et al. Impact of adult deformity correction: 261. Can we define clinically relevant DJK in cervical deformity surgery? Spine J. 2018;18(8 Suppl):S129S130.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13

    Protopsaltis TS, Ramchandran S, Kim HJ, et al. Analysis of early distal junctional kyphosis (DJK) after cervical deformity correction. Spine J. 2016;16(10):S355S356.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14

    Charlson M, Szatrowski TP, Peterson J, Gold J. Validation of a combined comorbidity index. J Clin Epidemiol. 1994;47(11):12451251.

  • 15

    Miller EK, Neuman BJ, Jain A, Daniels AH, Ailon T, Sciubba DM, et al. An assessment of frailty as a tool for risk stratification in adult spinal deformity surgery. Neurosurg Focus. 2017;43(6):E3.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Searle SD, Mitnitski A, Gahbauer EA, Gill TM, Rockwood K. A standard procedure for creating a frailty index. BMC Geriatr. 2008;8 24.

  • 17

    Vernon H, Mior S. The Neck Disability Index: a study of reliability and validity. J Manipulative Physiol Ther. 1991;14(7):409415.

  • 18

    Tetreault L, Kopjar B, Nouri A, Arnold P, Barbagallo G, Bartels R, et al. The modified Japanese Orthopaedic Association scale: establishing criteria for mild, moderate and severe impairment in patients with degenerative cervical myelopathy. Eur Spine J. 2017;26(1):7884.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 19

    Smith JS, Eastlack RK, Blaskiewicz DJ, Shaffrey CI, Schwab FJ, Bess S, et al. Reliability assessment of a novel cervical deformity classification system. In: International Meeting on Advanced Spine Techniques (IMAST). SRS;2014.Accessed September 30, 2021. https://www.srs.org/UserFiles/file/meetings/imast2014/IMAST14-Final-4web3.pdf

    • Search Google Scholar
    • Export Citation
  • 20

    Moses MJ, Tishelman JC, Zhou PL, Moon JY, Beaubrun BM, Buckland AJ, Protopsaltis TS. McGregor’s slope and slope of line of sight: two surrogate markers for chin-brow vertical angle in the setting of cervical spine pathology. Spine J. 2019;19(9):15121517.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 21

    Ayres EW, Protopsaltis TS, Lafage R, et al. 298. Predicting the magnitude of distal junctional kyphosis following cervical deformity correction. Spine J. 2019;19(9):S145.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 22

    Blondel B, Lafage V, Farcy JPP, Schwab F, Bollini G, Jouve JLL. Influence of screw type on initial coronal and sagittal radiological correction with hybrid constructs in adolescent idiopathic scoliosis. Correction priorities. Orthop Traumatol Surg Res. 2012;98(8):873878.

    • Crossref
    • PubMed
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