171. Overcorrection of the upper instrumented vertebra relative to the center of the femoral heads is associated with proximal junctional kyphosis

Abstract Introduction Although matching lumbar lordosis (LL) with pelvic incidence (PI) is an important surgical goal for adult spinal deformity (ASD), there is concern that overcorrection may lead to proximal junctional kyphosis (PJK). We introduce the upper instrumented vertebra–femoral angle (UIVFA) as a measure of appropriate postoperative position in the setting of lower thoracic to pelvis surgical correction for patients with sagittal imbalance. We hypothesize that a more posterior UIV position in relation to the center of the femoral head is associated with an increased risk of PJK given compensatory hyperkyphosis above the UIV. Methods In this retrospective cohort study, adult patients undergoing lower thoracic (T9–T12) to pelvis correction of ASD with a minimum of 2-year follow-up were included. UIVFA was measured as the angle subtended by a line from the UIV centroid to the femoral head center to the vertical axis. Patients who developed PJK and those who did not were compared with preoperative and postoperative UIVFA as well as change between postoperative and preoperative UIVFA (deltaUIVFA). Results Of 119 patients included with an average 3.6-year follow-up, 51 (42.9%) had PJK and 24 (20.2%) had PJF. Patients with PJK had significantly higher postoperative UIVFA (12.6 ± 4.8° vs. 9.4 ± 6.6°, p = 0.04), deltaUIVFA (6.1 ± 7.6° vs. 2.1 ± 5.6°, p < 0.01), postoperative pelvic tilt (27.3 ± 9.2 vs. 23.3 ± 11, p = 0.04), postoperative lumbar lordosis (47.7 ± 13.9° vs. 42.4 ± 13.1, p = 0.04) and postoperative thoracic kyphosis (44.9 ± 13.2 vs. 31.6 ± 18.8) than patients without PJK. With multivariate logistic regression, postoperative UIVFA and deltaUIVFA were found to be independent risk factors for PJK (p < 0.05). DeltaUIVFA was found to be an independent risk factor for PJF (p < 0.05). A receiver operating characteristic (ROC) curve for UIVFA as a predictor for PJK was established with an area under the curve of 0.67 (95% CI 0.59–0.76). Per the Youden index, the optimal UIVFA cut-off value is 11.5 degrees. Conclusion The more posterior the UIV is from the femoral head center after lower thoracic to pelvis surgical correction for ASD, the more patients are at risk for PJK. The greater the magnitude of posterior translation of the UIV from the femoral head center from preop to postop, the greater the likelihood for PJF.

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Open versus Minimally Invasive Approach (MIS) in Placement of Pedicle Screws at the Upper-Instrumented Vertebra (UIV) and the Effect on the Incidence of Proximal Junctional Kyphosis (PJK): A Prospective Randomized Controlled Study

The Spine Journal ◽

10.1016/j.spinee.2016.07.168 ◽

2016 ◽

Vol 16 (10) ◽

pp. S254

Author(s):

Emily Miller ◽

Tina Raman ◽

Floreana Naef ◽

Richard L. Skolasky ◽

Khaled M. Kebaish

Keyword(s):

Minimally Invasive ◽

Pedicle Screws ◽

Controlled Study ◽

Proximal Junctional Kyphosis ◽

Minimally Invasive Approach ◽

Invasive Approach ◽

Randomized Controlled ◽

Open Versus ◽

Upper Instrumented Vertebra ◽

Junctional Kyphosis

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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

Neurosurgical FOCUS ◽

10.3171/2020.5.focus20192 ◽

2020 ◽

Vol 49 (2) ◽

pp. E7

Author(s):

Ping-Guo Duan ◽

Praveen V. Mummaneni ◽

Joshua Rivera ◽

Jeremy M. V. Guinn ◽

Minghao Wang ◽

...

Keyword(s):

Spinal Deformity ◽

Adult Spinal Deformity ◽

Youden Index ◽

Proximal Junctional Kyphosis ◽

Mineral Density ◽

Hounsfield Units ◽

Significant Difference ◽

Upper Instrumented Vertebra ◽

Junctional Kyphosis

OBJECTIVEPatients 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.METHODSThe 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.RESULTSThe 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).CONCLUSIONSIn 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.

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Optimal tether configurations and preload tensioning to prevent proximal junctional kyphosis: a finite element analysis

Journal of Neurosurgery Spine ◽

10.3171/2018.10.spine18429 ◽

2019 ◽

Vol 30 (5) ◽

pp. 574-584 ◽

Cited By ~ 2

Author(s):

Thomas J. Buell ◽

Shay Bess ◽

Ming Xu ◽

Frank J. Schwab ◽

Virginie Lafage ◽

...

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Element Model ◽

Adjacent Segment ◽

Proximal Junctional Kyphosis ◽

Element Analysis ◽

Distal Fixation ◽

Upper Instrumented Vertebra ◽

The Impact ◽

Junctional Kyphosis

OBJECTIVEProximal junctional kyphosis (PJK) is, in part, due to altered segmental biomechanics at the junction of rigid instrumented spine and relatively hypermobile non-instrumented adjacent segments. Proper application of posteriorly anchored polyethylene tethers (i.e., optimal configuration and tension) may mitigate adjacent-segment stress and help prevent PJK. The purpose of this study was to investigate the impact of different tether configurations and tensioning (preloading) on junctional range-of-motion (ROM) and other biomechanical indices for PJK in long instrumented spine constructs.METHODSUsing a validated finite element model of a T7–L5 spine segment, testing was performed on intact spine, a multilevel posterior screw-rod construct (PS construct; T11–L5) without tether, and 15 PS constructs with different tether configurations that varied according to 1) proximal tether fixation of upper instrumented vertebra +1 (UIV+1) and/or UIV+2; 2) distal tether fixation to UIV, to UIV−1, or to rods; and 3) use of a loop (single proximal fixation) or weave (UIV and/or UIV+1 fixation in addition to UIV+1 and/or UIV+2 proximal attachment) of the tether. Segmental ROM, intradiscal pressure (IDP), inter- and supraspinous ligament (ISL/SSL) forces, and screw loads were assessed under variable tether preload.RESULTSPS construct junctional ROM increased abruptly from 10% (T11–12) to 99% (T10–11) of baseline. After tethers were grouped by most cranial proximal fixation (UIV+1 vs UIV+2) and use of loop versus weave, UIV+2 Loop and/or Weave most effectively dampened junctional ROM and adjacent-segment stress. Different distal fixation and use of loop versus weave had minimal effect. The mean segmental ROM at T11–12, T10–11, and T9–10, respectively, was 6%, 40%, and 99% for UIV+1 Loop; 6%, 44%, and 99% for UIV+1 Weave; 5%, 23%, and 26% for UIV+2 Loop; and 5%, 24%, and 31% for UIV+2 Weave.Tethers shared loads with posterior ligaments; consequently, increasing tether preload tension reduced ISL/SSL forces, but screw loads increased. Further attenuation of junctional ROM and IDP reversed above approximately 100 N tether preload, suggesting diminished benefit for biomechanical PJK prophylaxis at higher preload tensioning.CONCLUSIONSIn this study, finite element analysis demonstrated UIV+2 Loop and/or Weave tether configurations most effectively mitigated adjacent-segment stress in long instrumented spine constructs. Tether preload dampened ligament forces at the expense of screw loads, and an inflection point (approximately 100 N) was demonstrated above which junctional ROM and IDP worsened (i.e., avoid over-tightening tethers). Results suggest tether configuration and tension influence PJK biomechanics and further clinical research is warranted.

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The Impact of Global Alignment and Proportion Score and Bracing on Proximal Junctional Kyphosis in Adult Spinal Deformity

Global Spine Journal ◽

10.1177/21925682211001812 ◽

2021 ◽

pp. 219256822110018

Author(s):

Elizabeth L. Lord ◽

Ethan Ayres ◽

Dainn Woo ◽

Dennis Vasquez-Montes ◽

Yesha Parekh ◽

...

Keyword(s):

Spinal Deformity ◽

Chart Review ◽

Adult Spinal Deformity ◽

Retrospective Chart Review ◽

Global Alignment ◽

X Rays ◽

Proximal Junctional Kyphosis ◽

Upper Instrumented Vertebra ◽

The Impact ◽

Junctional Kyphosis

Study Design: Retrospective chart review. Objective: The goal of this study is to examine the relationship between global alignment and proportion (GAP) score and postoperative orthoses with likelihood of developing proximal junctional kyphosis (PJK). Methods: Patients who underwent thoracic or lumbar fusions of ≥4 levels for adult spinal deformity (ASD) with 1-year post-operative alignment x-rays were included. Chart review was conducted to determine spinopelvic alignment parameters, PJK, and reoperation. Results: A total of 81 patients were included; baseline and 1-year postoperative alignment did not differ between patients with and without PJK. There was no PJK in 53.1%, 29.6% had PJK from 10-20°, and 17.3% had severe PJK over 20° (sPJK). At baseline, 80% of patients had severely disproportioned GAP, 13.75% moderate, 6.25% proportioned. GAP improved across the population, but improved GAP was not associated with sPJK. Greater correction of the upper instrumented vertebra to pelvic angle (UIV-PA) was associated with a larger PJK angle (PJKA) change (R = -0.28) as was the 1 year T1-upper instrumented vertebra (T1-UIV) angle (R = 0.30), both P < .05. GAP change was not correlated with PJKA change. Postoperative orthoses were used in 46% of patients and did not impact sPJK. Conclusions: There was no correlation between PJK and GAP or change in GAP. Greater correction of UIV-PA and larger postop T1-UIV was associated with greater PJKA change; suggesting that the greater alignment correction led to greater likelihood of failure. Postoperative orthoses had no impact on PJK.

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Surgical Design Optimization of Proximal Junctional Kyphosis

Journal of Healthcare Engineering ◽

10.1155/2020/8886599 ◽

2020 ◽

Vol 2020 ◽

pp. 1-8

Author(s):

Li Peng ◽

Guangming Zhang ◽

Heng Zuo ◽

Lan Lan ◽

Xiaobo Zhou

Keyword(s):

Area Under The Curve ◽

Proximal Junctional Kyphosis ◽

Before And After ◽

The Difference ◽

Procedural Planning ◽

Upper Instrumented Vertebra ◽

Leave One Out ◽

Fully Connected ◽

The Relationship ◽

Junctional Kyphosis

Purpose. The objective of this study was to construct a procedural planning tool to optimize the proximal junction angle (PJA) to prevent postoperative proximal junctional kyphosis (PJK) for each scoliosis patient. Methods. Twelve patients (9 patients without PJK and 3 patients with PJK) who have been followed up for at least 2 years after surgery were included. After calculating the loading force on the cephalad intervertebral disc of upper instrumented vertebra of each patient, the finite-element method (FEM) was performed to calculate the stress of each element. The stress information was summarized into the difference value before and after operation in different regions of interest. A two-layer fully connected neural network method was applied to model the relationship between the stress information and the risk of PJK. Leave-one-out cross-validation and sensitivity analysis were implemented to assess the accuracy and stability of the trained model. The optimal PJA was predicted based on the learned model by optimization algorithm. Results. The mean prediction accuracy was 83.3% for all these cases, and the area under the curve (AUC) of prediction was 0.889. And the output variance of this model was less than 5% when the important factor values were perturbed in a range of 5%. Conclusion. Our approach integrated biomechanics and machine learning to support the surgical decision. For a new individual, the risk of PJK and optimal PJA can be simultaneously predicted based on the learned model.

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