Estimation of proximal junctional failure and associated risk factors in adult spine deformity surgery: an observational study from a single institution

Article information

Asian Spine J. 2025;.asj.2024.0405

Publication date (electronic) : 2025 March 4

doi : https://doi.org/10.31616/asj.2024.0405

Vishwajeet Singh¹, Marcelo Oppermann², Nathan Evaniew³, Alexandra Soroceanu³, Fred Nicholls³, Bradley Jacobs⁴, Kenneth Thomas³, Ganesh Swamy³

¹Division of Orthopaedic Surgery, Calgary Spine Program, University of Calgary, Calgary, AB, Canada

²Division of Neurosurgery, Department of Surgery, Western University, London, ON, Canada

³Division of Orthopaedic Surgery Spine Program, Department of Surgery, University of Calgary, Calgary, AB, Canada

⁴Division of Neurosurgery Spine Program, Department of Clinical Neurosciences, University of Calgary, Calgary, AB, Canada

Corresponding author: Vishwajeet Singh, Division of Orthopaedic Surgery, Department of Surgery, University of Calgary, Foothills Medical Center, 1403 29th ST NW, Calgary, Alberta T2N 2T9, Canada, Tel: +1-859-562-0207, Fax: +1-859-562-0207, E-mail: vishwajeet.singh@uky.edu

Received 2024 September 27; Revised 2024 November 4; Accepted 2024 December 12.

Abstract

Introduction

Mechanical failure at the proximal junctions remains the most challenging complication of adult spine deformity (ASD) surgery. Although a consensus definition of proximal junctional kyphosis (PJK) has been widely accepted and used, the description of proximal junctional failure (PJF) continues to evolve [1,2]. Glattes et al. [1] utilized the sagittal angle between the upper instrumented vertebra (UIV) and the vertebra above (UIV+1) to describe the proximal junctional angle (PJA). They defined PJK as having a PJA of >10° and a >10° difference in PJA between postoperative and preoperative lateral radiographs [2–5]. However, most patients identified as having PJK using this definition have been clinically asymptomatic [6]. The description appears simple because of its poor correlation with clinical outcomes [5]. A new PJK criterion has been proposed using 28° PJA and 22° PJA differences as cutoff values; however, its performance is yet to be tested in future studies [5]. PJF is increasingly employed to describe proximal junctional malalignment that requires intervention because of its strong correlation with patient outcomes [2,5,7].

PJF leads to worsening pain, disability, and neurological deficits and consequently is clinically more relevant than the radiological findings of PJK to describe junctional failure [4,7]. Apart from the magnitude of the PJA, several measurable radiological features have been included to present an objective description of PJF. PJA changes along with partial or complete fixation failure, UIV or UIV+1 fracture, or vertebral translation in the proximal junctional region strongly correlate with poor patient outcomes [4]. These findings represent an advanced junctional issue and often require extensive revision surgery [7]. The reported incidence of PJF ranges from 1.4% to 19%; however, the studies are limited by shorter follow-up duration, heterogeneous deformity cohorts, or single-surgeon series [8,9]. Given the limited tolerance for appropriate correction, a bias exists in the databases from which the knowledge is derived toward high numbers of revision cases and, thus, high numbers of three-column osteotomies.

PJF is a highly relevant indicator of junctional pathologies to clinicians; thus, PJF rates must be established from a constrained, homogenous spinal deformity dataset. Since 2010, the investigators at the University of Calgary have primarily employed anterolateral interbody fusion (IF) approaches for degenerated lumbar disc segments, which has led to a noticeable improvement in lumbar lordosis restoration in our practice. The institutional ASD dataset was used to estimate the PJF rates in this constrained primary spinal deformity cohort treated with anterolateral IF approaches. For this study, we hypothesized that we would experience fewer PJFs with improved alignment restoration and the use of PJK prophylaxis measures. The primary objective was to estimate the PJF rate using the institutional ASD dataset. The secondary objective was to assess the performance of prophylaxis measures and alignment changes in predicting PJF.

Materials and Methods

Results

In total, 157 adult patients who underwent surgery between 2011 and 2018 met the inclusion criteria, of which 130 were included in the sample after applying the exclusion criteria (<2 years of follow-up, n=22; incomplete radiological series, n=5). The baseline demographic, surgical, and radiographic characteristics of the patients are summarized in Tables 1 and 2 and Supplement 1.

Table 1

Summary of the baseline demographic and radiological parameters of the patients in the study

Table 2

The surgical characteristics of the patients in the study

The mean patient age was 64.6±8 years, and 73% of patients were females. Thirty-six patients (27.6%) had a history of single-level fusion or decompression surgery, and seven patients (5.4%) had osteoporosis and were on preoperative teriparatide. The median number of comorbidities was 2 (IQR, 1). An all-anterolateral or combined (anterolateral and posterior) IF approach was used. The combined IF approach was used in 121 patients (93%). Patients underwent multiple-level IF and thoracolumbar instrumentation, including sacropelvic fixation. The median instrumentation level was 8 (IQR, 7–8). The median levels of TLIF, ALIF, and LLIF performed were 1 (IQR, 1–1), 1 (1–1), and 3 (3–4), respectively. The UIV was the upper thoracic (T2–T4) in 31 (24%), lower thoracic (T10–T12) in 92 (71%), and upper lumbar (L1) in seven patients (5%). Fifty patients (38%) had posterior column osteotomies (PCO; Schwab types 1 and 2), and 9 (7%) had pedicle subtraction osteotomy. The employed PJK prophylaxis measures were proximal hooks in 18 (14%), UIV vertebroplasty in 33 (25.3%), and proximal tethers in 23 patients (17.7%). The median follow-up duration was 4.3 years (IQR, 2.5 years).

Moreover, 42 patients (32%) developed PJF, whereas no PJF developed in 88 (68%) during the follow-up. The mean patient ages in the PJF and non-PJF groups were 66.7±8 and 63.6±7.7, respectively (p=0.03). Thirty-two patients (36%) in the PJF group and 4 (10%) in the non-PJF group had a prior surgery (p=0.01). Other demographic, surgical, and preoperative radiological characteristics were comparable in both groups. Six patients (14.3%) with PJF had an upper thoracic UIV (T2–T4), and 34 (81%) had a lower thoracic (T10–T12) UIV. The mean follow-up durations for the PJF and non-PJF groups were 5.2±2.1 years and 4.4±2 years, respectively (p=0.03). The mean postop Cobb angles were 12.4°±6° in the PJF group and 18.4°±12.4° in the no-PJF group (p<0.01). The mean postop PJA values were 16.1°±7.4° in the PJF group and 13.1°±8.4° in the no-PJF group (p=0.04). Other postoperative radiological parameters were similar in both groups. Similarly, differences in the postoperative and preoperative radiological parameters were comparable in both groups, except for the difference in TK, PI–LL mismatch, and PJA. The TK differences for the PJF and non-PJF groups were 16.5°±10° and 14.6°±10.6° (p<0.01), PI–LL mismatch differences were 20.8°±16° and 15°±16° (p=0.05), and PJA differences were 10°±6.3° and 4.5°±4° (p<0.01), respectively (Fig. 1).

Fig. 1

Radiographs of a 50-year-old female with adult idiopathic scoliosis patient showing right thoracic, left thoracolumbar, and thoracolumbar kyphosis (A). The patient underwent T3-pelvis instrumented fusion. Postoperative images demonstrate reasonable sagittal and coronal correction. Postoperative proximal junctional angle (PJA) measures 5° and a change of 2° from preoperative images (B). Five-year follow-up images demonstrate maintained PJA (5°). The patient had a slight loss of coronal balance following revision surgery for L5–S1 pseudoarthrosis (C).

Characteristics of patients with PJF

At the final follow-up, 42 patients (32.3%) had PJF. Their mean ΔPJA was 26°±8.2° (Table 3). Thirty-three patients (79%) had a final PJA >20°, 4 (10%) had an additional UIV/UIV+1 fracture, and 5 (12%) had an additional screw dislodgement or fixation failure (Fig. 2).

Table 3

Summary of the characteristics of patients in the PJF group

Fig. 2

Radiographs of a 68-year-old female with degenerative scoliosis show predominant right lumbar curve and lumbar kyphosis (A). The patient underwent L1–S1 anterolateral interbody fusion, posterior T10-pelvis instrumented fusion, and T9–T10 vertebroplasty. Postoperative proximal junctional angle (PJA) was 10°, a difference of 5° from preoperative, as demonstrated by images obtained after the surgery (B). The final PJA at 5-year follow-up images was 30°. This patient remained clinically asymptomatic despite worsening in PJA (C).

Assessment of PJF predictors

The adjusted analysis using the multivariable regression model demonstrated a lower association between PJF and proximal hook use (OR, 0.12; 95% CI, 0.02–0.59; p=0.01) and proximal tether use (OR, 0.22; 95% CI, 0.04–0.82; p=0.03). PJF exhibited an increased association with postoperative changes in TK (OR, 1.06; 95% CI, 1.02–1.11; p<0.01) and PJA (OR, 1.23; 95% CI, 1.12–1.37; p<0.01). Bootstrapped sampling demonstrated a large uncertainty in the estimates (standard error=4.16) and high bias (−1.3) for the proximal hook variable. Other predictor variables, including age and osteoporosis, were not significantly associated with PJF (Table 4).

Table 4

Association measures of PJF and the covariates from the multivariate regression model, including their respective ORs and 95% CIs

Characteristics of patients with PJF who underwent reoperation

Twenty-eight patients (67%) with PJF underwent reoperation until the last recorded follow-up. The mean time-to-reoperation from the index surgery was 12.2±10 months. Based on the Kaplan-Meier survival curve, the PJF reoperation rates were 12.3%, 19.3%, 22.6%, 23.9%, and 26.8% at 12, 24, 36, 48, and 60 months, respectively (Fig. 3). The mean ΔPJA in this subset was 26°±9.2°. Nineteen patients (68%) had a final PJA of >20°, 4 (14.2%) had an additional UIV/UIV+1 fracture, and 5 (18%) had an additional screw dislodgement or fixation failure. For those who underwent reoperations for PJFs, 6 (21%) had upper thoracic UIV, 20 (71%) had lower thoracic UIV, and 2 (7.1%) had upper lumbar UIV (Fig. 4). All patients underwent reoperation with cephalad extension of instrumentation, of which recurrent PJF developed in six patients (21%) who required reoperation (Supplement 2).

Fig. 3

The Kaplan-Meier survivor curve shows reoperation rates for patients with proximal junctional failure during their follow-up. CI, confidence interval.

Fig. 4

Radiographs of a 70-year-old female with degenerative scoliosis, left lumbar curve, loss of lumbar lordosis, and reasonable coronal and sagittal balance (A). The patient underwent L1–L4 lateral interbody fusion, L4–S1 transforaminal lumbar interbody fusion and posterior T10-pelvis instrumented fusion. Postoperative proximal junctional angle (PJA) worsened by 5° to 18° (B). Eighteen months follow-up radiographs demonstrate further worsening of PJA to 35° with evidence of screw loosening. This patient was clinically symptomatic and was reoperated with the extension of instrumentation to the upper thoracic region (C).

Discussion

PJF is a commonly encountered junctional complication in ASD surgeries [10,11]. Junctional failures, described as PJK using the Glattes criteria, tend to overestimate the burden of mechanical complications [5,7]. PJF strongly correlates with the PROs and reoperation risks, and the definition aids in clinical decision-making [7]. In this study, the Hart-ISSG criteria was used to define PJF, and the estimated PJF rate was 32%. Of all patients with PJF, 78% had >20° of postoperative PJA difference, 10% had an additional UIV/UIV+1 fracture or translation, and 12% had an additional fixation failure. Twenty-eight patients (67%) with PJF and 22% (28/130) of the entire cohort underwent reoperation within 2 years of the index procedure. The use of proximal tethers and the postoperative differences in PJA and TK demonstrated a significant association with PJF development.

PJK rates have been extensively studied, with reported rates varying from 17% and 61.7% [6,12]. Several large series have indicated a poor correlation between PJK and PROs or reoperations [5,6,10]. Given the limited clinical utility of the PJK definition, PJF estimation has become significant. A large retrospective series of patients with ASD reported a PJF rate of 1.4% [8]. The authors defined PJF as symptomatic PJKs that require surgery. In another study, the same authors reported a PJF rate of 19% in 119 patients with ASD using a revised PJF definition [13], where PJF was defined as increased PJA >20° from the preoperative value, PJK requiring reoperation or worsening in one Scoliosis Research Society [SRS]-Schwab sagittal modifier domain [14]. The lower PJF rate in these studies could be attributed to the inclusion of a heterogeneous patient cohort with pathology ranging from primary idiopathic to iatrogenic deformities following revision surgery or fixed sagittal imbalance. These studies have also inconsistently used sacropelvic fixation. Hart et al. [15] proposed a modification in the PJF definition by including radiological findings (UIV/UIV fracture and fixation failure or posterior ligamentous disruption) to the Glattes criteria. In their series, 57 patients (4.7%) with ASD had PJF; however, their patient population was also heterogeneous, comprising revisions, iatrogenic deformity, fixed sagittal imbalance, and inconsistent instrumentation length [15]. In the present study, PJF was defined using Hart’s and additional PJA criteria (final PJA >20°) as described by Lazaro et al. [7]. In this retrospective review of 160 patients with adult thoracolumbar deformity, the authors reported a PJF rate of 28.7%. Their patient enrollment criteria were similar to ours and included patients with primary adult deformity having extended instrumentation to the pelvis. Although our PJF rate is higher than that in previous reports, it closely follows the PJF rate reported by Lazaro et al. [7].

PJK has a multifactorial etiology, which is influenced by several patient-related factors such as age, body mass index (BMI), bone mineral density, paraspinal muscle atrophy, preexisting TK, preoperative PJA, sagittal malalignment, and surgical factors such as soft tissue preservation, persistent sagittal malalignment, and sagittal under- or overcorrection [16,17]. Several strategies for achieving harmonious alignment to prevent PJK have been described, including the global alignment and proportion (GAP) scores [18] and age-appropriate SRS-Schwab alignment descriptors [19]. Various PJK prophylaxis measures have varying success [7,20]. In this study, the effect of postoperative alignment correction and prophylaxis measures on the occurrence of PJF was investigated. The postoperative changes in PJA and TK, as well as the use of proximal tethers, were significantly associated with PJF. The use of proximal hooks showed only a weak association with PJF, and its estimates had a high variability. Thus, this may be underpowered to adequately assess this association because of the considerable heterogeneity within the subset of patients treated with proximal hooks. Other changes in the alignment parameters or PJK prophylaxis measures were not associated with PJF. These findings are in contrast to those noted by Lazaro et al. [7], who reported that prophylactic measures did not offer protective benefits.

Rasouligandomani et al. [18] proposed a sagittal alignment and mechanical integrated score (SAMIS) system, which adds to the biomechanical descriptors in the geometrical descriptor-based system of the GAP classification [21]. The SAMIS score is proposed to predict PJF risk better than previous prediction methods. The new SAMIS considers the bending moment to be a function of the BMI. Although BMI, a crucial PJF risk factor, was not collected for each patient in our cohort, we could not assess its effect on PJF. In the present study, no significant association was found between osteoporosis and PJF. The osteoporosis variable had a large effect size (OR, 4.37), indicating a positive association; however, the estimate showed high variability. This finding should be interpreted with caution because the heterogeneity and inadequate sample size in this subset must be considered. In addition, patients with osteoporosis were on teriparatide therapy preoperatively, and a short therapy duration may have been ineffective in preventing PJF in these patients.

In this study, 28 patients (67%) underwent reoperation. Although the decision to reoperate is multifactorial [7,12,15], the patient’s perceived disability and consent are decisive. All patients with acute PJF, i.e., those with an additional fixation failure (14%) or UIV fracture or translation (18%), underwent reoperation. Patients’ choices primarily determined the decision to reoperate. The reoperation rate in this study is higher than that reported in the literature [7,15]. Older patients (mean age, 66.7 years) with higher baseline sagittal decompensation (mean SVA=52 mm, mean TK=32.4°, mean PJA=6.4°) may have contributed to the higher reoperation rates in our cohort. The mean time-to-reoperation (12.2 months) was similar to that described in the literature. The Kaplan-Meier survival plot showed that most patients underwent reoperations within 2 years of the index procedure [7,15].

The result of this study demonstrates that a third of patients with ASD undergoing surgery develop PJFs, and the use of proximal tethers and postoperative PJA and TK changes are associated with PJF. This study is unique in defining the PJF rates in a constrained ASD population and further confirms the findings of Lazaro et al. [7].

The notable strengths of this study are the analysis of a homogenous patient population, patients with primary sagittal decompensation, a constrained patient cohort, and a long follow-up from the prospective institutional database. However, a few limitations require attention. Despite the consecutive patient enrollment, the results are subject to potential selection biases owing to their retrospective nature. PRO scores were not collected for all patients, and their relationship with PJF or PJF reoperations could not be ascertained. BMI and the lack of information on muscle health at the UIV levels are other significant variables not analyzed in this study. This is a multiple-surgeon series from a single institution with a similar case selection and surgical approach; however, a performance bias cannot be excluded. Nevertheless, the results of this study provide valuable information on the PJF rates and their potential risk factors. A larger prospective study incorporating BMI and PROs is warranted to further validate our findings and establish associations with PJF.

Conclusions

PJF is the most challenging junctional complication of adult spinal deformity surgery. In this study, the PJF rate was 32%, of which 67% of the patients underwent reoperation. Postoperative changes in PJA and TK and the use of proximal tethers were significantly associated with PJF.

Supplementary Materials

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