Ligament Augmentation With Mersilene Tape Reduces the Rates of Proximal Junctional Kyphosis and Failure in Adult Spinal Deformity

Functional Alignment Within the Fusion in Adult Spinal Deformity (ASD) Improves Outcomes and Minimizes Mechanical Failures

STUDY DESIGN

Retrospective review of an adult deformity database.

OBJECTIVE

To identify pelvic incidence (PI) and age-appropriate physical function alignment targets using a component angle of T1-pelvic angle within the fusion to define correction and their relationship to proximal junctional kyphosis (PJK) and clinical outcomes.

SUMMARY OF BACKGROUND DATA

In preoperative planning, a patient's PI is often utilized to determine the alignment target. In a trend toward more patient-specific planning, age-specific alignment has been shown to reduce the risk of mechanical failures. PI and age have not been analyzed with respect to defining a functional alignment.

METHODS

A database of patients with operative adult spinal deformity was analyzed. Patients fused to the pelvis and upper-instrumented vertebrae above T11 were included. Alignment within the fusion correlated with clinical outcomes and PI. Short form 36-Physical Component Score (SF36-PCS) normative data and PI were used to compute functional alignment for each patient. Overcorrected, under-corrected, and functionally corrected groups were determined using T10-pelvic angle (T10PA).

RESULTS

In all, 1052 patients met the inclusion criteria. T10PA correlated with SF36-PCS and PI (R=0.601). At six weeks, 40.7% were functionally corrected, 39.4% were overcorrected, and 20.9% were under-corrected. The PJK incidence rate was 13.6%. Overcorrected patients had the highest PJK rate (18.1%) compared with functionally (11.3%) and under-corrected (9.5%) patients ( P <0.05). Overcorrected patients had a trend toward more PJK revisions. All groups improved in HRQL; however, under-corrected patients had the worst 1-year SF36-PCS offset relative to normative patients of equivalent age (-8.1) versus functional (-6.1) and overcorrected (-4.5), P <0.05.

CONCLUSIONS

T10PA was used to determine functional alignment, an alignment based on PI and age-appropriate physical function. Correcting patients to functional alignment produced improvements in clinical outcomes, with the lowest rates of PJK. This patient-specific approach to spinal alignment provides adult spinal deformity correction targets that can be used intraoperatively.

Use of Tethers for Proximal Junctional Kyphosis Prophylaxis in Adult Spinal Deformity Surgery: A Review of Current Clinical Evidence

BACKGROUND

Surgery for adult spinal deformity (ASD) often involves long-segment posterior instrumentation that introduces stress at the proximal junction that can result in proximal junctional kyphosis (PJK) or proximal junctional failure (PJF). Recently, the use of tethers at the proximal junction has been proposed as a means of buffering the transitional stresses and reducing the risk of PJK/PJF. Our objectives are to summarize the clinical literature on proximal junctional tethers for PJK/PJF prophylaxis.

METHODS

Articles published between 1 January 2000 and 10 November 2022 were identified via a PubMed search using combinations of the search terms "spine surgery," "ASD," "complication," "surgery," "PJK," "PJF," "tether," "sublaminar band," and "prophylaxis." No restrictions were placed on the number of patients, surgical indications, or surgical procedures. Relevant articles were reviewed and summarized.

RESULTS

Fifteen articles were identified, including 2 prospective cohorts (Level II), 10 retrospective cohorts (Level III), and 3 retrospective case series (Level IV). All studies were published between 2016 and 2022, and all focused on ASD patient populations. The mean age in each study ranged from 55 to 69 years, and most studies had a mean follow-up of at least 12 months (range, 5.5-45.4 months). Eleven studies used a polyethylene tether, 2 used soft sublaminar cables, and 2 used semitendinous allograft. The tether extended to the UIV+1 or UIV+2, passing either through or around the spinous processes, in 13 studies. In the remaining 2 studies, the tether was passed sublaminar at the UIV+1. Fourteen studies favored the use of tethers with regard to reduction of PJK/PJF rates, and one demonstrated similar rates of PJK between the tether and no-tether groups.

CONCLUSIONS

PJK/PJF remain major challenges in ASD surgery. Most early studies suggest that the use of tethers for ligamentous augmentation may help to mitigate the development of PJK/PJF. However, the multifactorial etiology of PJK/PJF makes it unlikely that any single technique will solve this complex problem. Further study is needed to address not only the effectiveness of junctional tethers but also to clarify whether there are optimal tether configurations, tether materials, and tether tension.

LEVEL EVIDENCE

3.

Clinical and Economic Impact of Proximal Junctional Kyphosis on Pediatric and Adult Spinal Deformity Patients

The common goal of pediatric and adult spinal reconstructive procedures is to minimize long-term risk of disability, pain, and mortality. A common complication that has proved particularly problematic in the adult spinal deformity population and that has been an area of increased research and clinical focus is proximal junctional kyphosis (PJK). The incidence of PJK ranges from 10%-40% based on criteria used to define the condition. Clinically, PJK complication is associated with increased pain, decreased self-image and Scoliosis Research Society scores, and severe neurological injuries affecting the patient's quality of life. Economically, direct costs of PJK complication-associated revision surgery ranges from $20,000 to $120,000, which places an enormous burden on patients, providers, and payers. To mitigate the risk of PJK occurrence postoperatively, it is paramount to develop consistent guidelines in defining and classifying PJK in addition to extensive preoperative planning and risk stratification that is patient specific. This article will provide an overview on the clinical and economic impact of PJK in pediatric and adult spine deformity patients with an emphasis on the role of patient factors and predictive analytics, challenges in developing a consistent PJK classification, and current treatment and prevention strategies.

Introduction of a New Radiographic Parameter to Predict Proximal Junctional Kyphosis in Adult Spinal Deformity: UIVPTA (Uppermost Instrumented Vertebra-Pelvic Tilt Angle)

OBJECTIVE

To introduce a new sagittal parameter, uppermost instrumented vertebra-pelvic tilt angle (UIVPTA), and to determine the effects on the proximal junctional kyphosis (PJK) development in adult spinal deformity (ASD) surgery.

METHODS

Patients ≥ 60 years with ASD who underwent low thoracic spine to pelvis fusion with a minimum of 2-years of follow-up were included in this study. Two groups were created according to PJK development. Various clinical and radiographic factors were compared between PJK and non-PJK groups to identify the risk factors for PJK. Cutoff value of UIVPTA for PJK development was calculated using receiver operating characteristic curve according to different pelvic incidence groups. Linear regression analysis was performed to identify factors to affect UIVPTA.

RESULTS

One hundred fifity-one patients were included in this study. There were 135 female patients (89.4%). Mean age was 70.5 years. PJK developed in 65 patients (43.0%). Multivariate analysis showed that overcorrection relative to age-adjusted pelvic incidence (PI) minus lumbar lordosis (LL) (PI-LL) target and lower UIVPTA were independent risk factors for PJK. The cutoff value of UIVPTA for PJK development was calculated as 4.0° in patients with PI less than 45°, 9.5° in patients with PI between 45° and 60°, and 13.0° in patients with PI greater than 60°. Linear regression analysis showed that UIVPTA was positively affected by postoperative values of LL (coefficient = 0.505), PI-LL (coefficient = 0.674), and pelvic tilt (coefficient = 0.286).

CONCLUSION

Optimal correction within the age-adjusted PI-LL combined with keeping UIVPTA within optimal range is suggested for the prevention of PJK.

Proximal Junctional Failure in Adult Spinal Deformity Surgery: An In-depth Review

Adult spinal deformity (ASD) surgery aims to correct abnormal spinal curvature in adults, leading to improved functionality and reduced pain. However, this surgery is associated with various complications, one of which is proximal junctional failure (PJF). PJF can have a significant impact on a patient's quality of life, necessitating a comprehensive understanding of its causes and the development of effective management strategies. This review aims to provide an in-depth understanding of PJF in ASD surgery. PJF is a complex complication resulting from a multitude of factors including patient characteristics, surgical techniques, and postoperative management. Age, osteoporosis, overcorrection of sagittal alignment, and poor bone quality are identified as significant risk factors. The clinical implications of PJF are substantial, often requiring revision surgery and causing a considerable decrease in patients' quality of life. Prevention strategies include careful preoperative planning, appropriate patient selection, and optimization of surgical techniques. Treatment often necessitates a multifaceted approach, including surgical intervention and the management of underlying risk factors. Predictive modeling is an emerging field that may offer a promising avenue for the risk stratification of patients and individualized preventive strategies. A thorough understanding of PJF's pathogenesis, risk factors, and clinical implications is essential for surgeons involved in ASD surgery. Current preventive measures and treatment strategies aim to mitigate the risk and manage the complications of PJF, but the complication cannot be entirely prevented. Future research should focus on the development of more effective preventive and treatment strategies, and predictive models could be valuable in this pursuit.

Proximal Junctional Kyphosis or Failure After Adult Spinal Deformity Surgery - Review of Risk Factors and Its Prevention

Proximal junction kyphosis (PJK) is a common imaging finding after long-level fusion, and proximal junctional failure (PJF) is an aggravated form of the progressive disease spectrum of PJK. This includes vertebral fracture of upper instrumented vertebra (UIV) or UIV+1, instability between UIV and UIV+1, neurological deterioration requiring surgery. Many studies have reported on PJK and PJF after long segment instrumentation for adult spinal deformity (ASD). In particular, for spine deformity surgeons, risk factors and prevention strategies of PJK and PJF are very important to minimize reoperation. Therefore, this review aims to help reduce the occurrence of PJK and PJF by updating the latest contents of PJK and PJF by 2023, focusing on the risk factors and prevention strategies of PJK and PJF. We conducted a search on multiple database for articles published until February 2023 using the search keywords "proximal junctional kyphosis," "proximal junctional failure," "proximal junctional disease," and "adult spinal deformity." Finally, 103 papers were included in this study. Numerous factors have been suggested as potential risks for the development of PJK and PJF, including a high body mass index, inadequate postoperative sagittal balance and overcorrection, advanced age, pelvic instrumentation, and osteoporosis. Recently, with the increasing elderly population, sarcopenia has been emphasized. The quality and quantity of muscle in the surgical site have been suggested as new risk factor. Therefore, spine surgeon should understand the pathophysiology of PJK and PJF, as well as individual risk factors, in order to develop appropriate prevention strategies for each patient.

The efficacy of prophylactic vertebroplasty for preventing proximal junctional complications after spinal fusion: a systematic review

BACKGROUND CONTEXT

Prophylactic vertebroplasty (VP) is performed at the upper level of instrumentation during spinal fusion to reduce the risk of proximal junctional kyphosis (PJK), proximal junctional fracture (PJFx), and proximal junctional failure (PJF). This study investigated the effect of VP on patient outcomes after spinal fusion.

PURPOSE

The aim of this systematic review was to evaluate the effect of prophylactic VP on the incidence of PJK in patients with spinal fusion.

STUDY DESIGN/SETTING

Level III, systematic review without meta-analysis.

PATIENT SAMPLE

Adult patients undergoing spinal fusion with VP.

METHODS

A PRISMA-compliant systematic literature review was conducted using PubMed/MEDLINE, Cochrane, and Embase. Included studies were published in English between January 1, 2001, and May 27, 2021, and reported primary data on adult patients undergoing spinal fusion with VP. Studies were excluded for insufficient surgical details; treatment for vertebral compression fracture; and case series and/or reports with <5 patients. The Newcastle-Ottawa Scale was used to assess risk of bias. The primary outcome of interest was PJK. Other outcomes included PJFx, PJF, and adverse events (eg, cement extravasation). Data were expressed as descriptive statistics.

RESULTS

Eight studies with 685 total patients (VP: 293 [42.8%]; No VP: 392 (57.2%)) were included. Five studies were comparative and three were single-arm. PJK incidence was reported in five studies (three comparatives, two single-arm) and ranged from 7.9% to 46.4%; incidence was lower in patients with VP in two of three (66.7%) comparative studies, and equal in one of three (33.3%). PJFx was reported in five studies (four comparatives, one single-arm) and ranged from 0.0% to 39.3%; incidence was lower in the VP group in two of four (50.0%) comparative studies, equal in one of four (25.0%), and higher in one of four (25.0%). PJF was reported in five studies (three comparatives, two single-arm) and ranged from 0.0% to 39.3%; incidence was lower in the VP group in two of three (66.7%) comparative studies and equal in one of three (33.3%). Cement extravasation was reported by four studies and ranged from 0% (0/36) to 48.3% (57/118) in patients with prophylactic VP.

CONCLUSIONS

Evidence on whether prophylactic VP decreases the incidence of PJK, PJFx, and PJF after spinal fusion is inconclusive and conflicting. Additionally, the risk of cement extravasation following prophylactic VP could not be evaluated due to insufficient evidence. Further research is needed to determine whether VP has a significant impact on patient outcomes and risks.

Influence of configuration and anchor in ligamentous augmentation to prevent proximal junctional kyphosis: A finite element study

Ligament augmentation has been applied during spinal surgery to prevent proximal junctional kyphosis (PJK), but the configuration and distal anchor strategies are diverse and inconsistent. The biomechanics of different ligament augmentation strategies are, therefore, unclear. We aimed to create a finite element model of the spine for segments T6–S1. Model Intact was the native form, and Model IF was instrumented with a pedicle screw from segments T10 to S1. The remaining models were based on Model IF, with ligament augmentation configurations as common (CM), chained (CH), common and chained (CHM); and distal anchors to the spinous process (SP), crosslink (CL), and pedicle screw (PS), creating SP-CH, PS-CHM, PS-CH, PS-CM, CL-CHM, CL-CH, and CL-CM models. The range of motion (ROM) and maximum stress on the intervertebral disc (IVD), PS, and interspinous and supraspinous ligaments (ISL/SSL) was measured. In the PS-CH model, the ROM for segments T9–T10 was 73% (of Model Intact). In the CL-CHM, CL-CH, CL-CM, PS-CM, and PS-CHM models, the ROM was 8%, 17%, 7%, 13%, and 30%, respectively. The PS-CH method had the highest maximum stress on IVD and ISL/SSL, at 80% and 72%, respectively. The crosslink was more preferable as the distal anchor. In the uppermost instrumented vertebrae (UIV) + 1/UIV segment, the CM was the most effective configuration. The PS-CH model had the highest flexion load on the UIV + 1/UIV segment and the CL-CM model provided the greatest reduction. The CL-CM model should be verified in a clinical trial. The influence of configuration and anchor in ligament augmentation is important for the choice of surgical strategy and improvement of technique.

Association between lower Hounsfield units and proximal junctional kyphosis and failure at the upper thoracic spine

OBJECTIVE

The aim of this study was to analyze risk factors and avoidance techniques for proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) in the upper thoracic spine with an emphasis on bone mineral density (BMD) as estimated by Hounsfield units (HU).

METHODS

A retrospective chart review identified patients at least 50 years of age who underwent instrumented fusion extending from the pelvis to an upper instrumented vertebra (UIV) between T1 and T6 and had a preoperative CT, pre- and postoperative radiographs, and a minimum follow-up of 12 months. HU were measured in the UIV, the vertebral body cephalad to the UIV (UIV+1), and the L3 and L4 vertebral bodies. Numerous perioperative variables were collected, including basic demographics, smoking and steroid use, preoperative osteoporosis treatment, multiple frailty indices, use of a proximal junctional tether, UIV soft landing, preoperative dual-energy x-ray absorptiometry, spinopelvic parameters, UIV screw tip distance to the superior endplate, UIV pedicle screw/pedicle diameter ratio, lumbar lordosis distribution, and postoperative spinopelvic parameters compared with age-adjusted normal values.

RESULTS

Eighty-one patients were included in the study (21 men and 60 women) with a mean (SD) age of 66 years (6.9 years), BMI of 29 (5.5), and follow-up of 38 months (25 months). Spinal fusion constructs at the time of surgery extended from the pelvis to a UIV of T1 (5%), T2 (15%), T3 (25%), T4 (33%), T5 (21%), and T6 (1%). Twenty-seven patients (33%) developed PJK and/or PJF; 21 (26%) had PJK and 15 (19%) had PJF. Variables associated with PJK/PJF with p < 0.05 were included in the multivariable analysis, including HU at the UIV/UIV+1, HU at L3/L4, DXA femoral neck T-score, UIV screw tip distance to the superior endplate, UIV pedicle screw/pedicle diameter ratio, and postoperative lumbar lordosis distribution. Multivariable analysis (area under the curve = 0.77) demonstrated HU at the UIV/UIV+1 to be the only independent predictor of PJK and PJF with an OR of 0.96 (p = 0.005). Patients with < 147 HU (n = 27), 147-195 HU (n = 27), and > 195 HU (n = 27) at the UIV/UIV+1 had PJK/PJF rates of 59%, 33%, and 7%, respectively.

CONCLUSIONS

In patients with upper thoracic-to-pelvis spinal reconstruction, lower HU at the UIV and UIV+1 were independently associated with PJK and PJF, with an optimal cutoff of 159 HU that maximizes sensitivity and specificity.

Clinically relevant biomechanical properties of three different fixation techniques of the upper instrumented vertebra in deformity surgery

OBJECTIVE

Adjacent segment disease, junctional kyphosis/failure and pseudarthrosis can negatively impact the mid to long-term outcome in spinal deformity surgery. These complications might be influenced by upper instrumented vertebra (UIV) fixation techniques. In this study we analyze key biomechanical properties of three different UIV fixation techniques and define their ideal clinical use based on patient-specific risk profiles using a finite element analysis (FEA) model.

METHODS

A T9-pelvis posterior instrumented spinal fusion was assumed. Three different FEA models were created based on the UIV fixation technique: T9 pedicle screws (PS); T9 cortical bone screws (CBS); T9 transverse process hooks (TPH). The three FEA models consisted of T8-T10 bone and ligamentous anatomy derived from a CT scan of a healthy patient as well as spinal implants consisting of either pedicle screws, cortical bone screws or transverse process hooks as well as cobalt chromium rods. The FEA models were constrained at T10, axial load as assumed for a healthy 80 kg male during flexion, extension and lateral bending were applied. As surrogate markers for risk of proximal junctional kyphosis, proximal junctional failure, adjacent segment disease and pseudarthrosis the following biomechanical parameters were calculated: UIV range of motion (ROM); intradiscal stress at UIV/UIV + 1; UIV intravertebral stress and screw pull out forces. One-way ANOVA analyses have been performed to compare biomechanical outcome parameters between the three construct variants under investigation.

RESULTS

UIV-ROM was restricted during flexion/extension/lateral bending by: PS: 73%/80%/86%, CBS: 71%/81%/85% and TPH: 62%/76%/85%. Average intradiscal stress at UIV/UIV + 1 during flexion/extension/lateral bending was (Mega Pascal, MPa): PS 0.42/0.44/0.38, CBS 0.49/0.4/0.44, TPH 0.66/0.51/0.58; average intravertebral stress of the UIV superior endplate during flexion/extension/lateral bending was (MPa): PS 2.23/2.12/2.21, CBS 1.87/1.98/1.8, TPH 1.67/0.98/1.53. Screw pull-out forces (N) at UIV during flexion/extension/lateral bending were: PS 476/320/375, CBS 444/245/308. Statistically significant differences were found for intradiscal stress as well as vertebral body average stress (p = 0.02 and p = 0.02).

CONCLUSION

Different UIV fixation techniques carry different biomechanical properties. Pedicle screw fixation is the most rigid, leading to the highest UIV stress and UIV screw pull out forces. Cortical bones screw fixation is similarly rigid; however, UIV stress and UIV screw pull out is significantly lower. Transverse process hook fixation is the least rigid, with the lowest UIV stress, however highest intradiscal stress at UIV/UIV + 1. Thus, these biomechanical differences may help select optimal UIV fixation techniques according to patient specific risk factors.

Biomechanical Effects of Proximal Polyetheretherketone Rod Extension on the Upper Instrumented and Adjacent Levels in a Human Long-Segment Construct: A Cadaveric Model

OBJECTIVE

The high mechanical stress zone at the sudden transition from a rigid to flexible region is involved in proximal junctional kyphosis (PJK) physiopathology. We evaluated the biomechanical performance of polyetheretherketone (PEEK) rods used as a nontraditional long semirigid transition phase from a long-segment metallic rod construct to the nonfused thoracic spine.

METHODS

Pure moment range of motion (ROM) tests (7.5 Nm) were performed on 7 cadaveric spine segments followed by compression (200 N). Specimens were tested in the following conditions: (1) intact; (2) T10-pelvis pedicle screws and rods (PSRs); and (3) extending the proximal construct to T6 using PEEK rods (PSR+PEEK). T10-11 rod strain, T9 anterolateral bone strain, and T10 screw bending moments were analyzed.

RESULTS

At the upper instrumented vertebra (UIV)+1, PSR+PEEK versus PSR significantly decreased ROM in flexion (115%, p = 0.02), extension (104%, p = 0.003), left lateral bending (46%, p = 0.02), and right lateral bending (63%, p = 0.008). Also, at UIV+1, PSR+PEEK versus intact significantly decreased ROM in flexion (111%, p = 0.01) and extension (105%, p = 0.003). The UIV+1 anterior column bone strain was significantly reduced with PSR+PEEK versus PSR during right lateral bending (p = 0.02). Rod strain polarities reversed with PEEK rods in all loading directions except compression.

CONCLUSION

Extending a long-segment construct using PEEK rods caused a decrease in adjacent-level hypermobility as a consequence of long-segment immobilization and also redistributed the strain on the UIV and adjacent levels, which might contribute to PJK physiopathology. Further studies are necessary to observe the clinical outcomes of this technique.