Standardized translaminar spinal tethering to prevent proximal junctional kyphosis in adult spinal deformity correction surgery

doi:10.21203/rs.3.rs-5291632/v1

Purpose:This study evaluated whether standardized proximal translaminar spinal tethering at the upper instrumented vertebra (UIV) +1 and UIV+2 reduces the incidence of proximal junctional kyphosis (PJK) and the need for revision surgery in patients undergoing thoraco-lumbar deformity correction for adult spinal deformity (ASD).

Methods:A retrospective cohort study was conducted on 59 adult patients who underwent thoraco-lumbar deformity correction surgery between October 2019 and August 2023. Patients were categorized into tethered (T) and non-tethered (NT) groups. Radiographic measurements were performed preoperatively, early postoperatively (≤3 months), and late postoperatively (>3 months) to assess PJK, defined as a proximal junctional angle (PJA) ≥ 10° and ≥ 10° greater than the corresponding preoperative measurement.

Results:Overall, 18 patients (30.5%) developed PJK, with no significant difference between tethered (12%) and non-tethered (20.5%) patients within the first 3 months (p=0.384). However, at late follow-up, the PJK rate was significantly higher in non-tethered (41.1%) compared to tethered (16%) patients (p=0.037), with non-tethered patients being 3.67 times more likely to develop PJK (95% CI = 1.03-13.07). Kaplan-Meier analysis showed a significant reduction in time-dependent PJK development for tethered patients (p=0.027). Revision surgery was required in 11.8% of non-tethered patients compared to 4% of tethered patients (p=0.289).

Conclusion:Proximal translaminar tethering at UIV+1 and UIV+2 effectively reduces the incidence of PJK in patients undergoing thoraco-lumbar deformity correction. However, the effect on surgical revision rates due to PJK remains unclear, warranting further long-term prospective studies.

The treatment of adult spinal deformity (ASD) is becoming increasingly important due to the aging global population, with nearly two-thirds of patients over the age of 59 affected.[1] Currently, instrumented spinal fusion and deformity correction surgery is the main approach for operative treatment of ASD. However, multi-segmental instrumentation continues to pose clinical challenges due to high biomechanical demands and overall complication rates up to 55%.[2]

One of the most frequently encountered complications following deformity correction surgery for ASD is adjacent segment degeneration. Here, fixed segments after spinal instrumentation may create an increased load on the proximal segments, leading to accelerated degeneration and potential radiographic and clinical deterioration.[3] A radiographically prevalent form of adjacent segment degeneration is proximal junctional kyphosis (PJK) with reported incidence rates up to 61.7%.[4] Risk factors of developing PJK include advanced age, high body mass index, and low bone quality.[5] Importantly, PJK carries the risk of proximal junctional failure (PJF), which is defined as fracture of the upper instrumented vertebra (UIV) or UIV + 1, posterior osseo-ligamentous disruption, or pull out of instrumentation at UIV, and symptomatic PJK requiring surgical treatment.[3]

To limit the risk of adjacent segment degeneration in deformity correction surgery, several techniques have meanwhile been proposed to more evenly distribute the load on the proximal segments of long spinal instrumentation constructs. Among these, proximal semi-rigid spinal tethering has demonstrated promising results in both biomechanical and clinical studies. However, these techniques are not yet standardized, widespread and the clinical evidence supporting their effectiveness still remains limited.[6] Against this background, here we assessed the effect of standardized proximal translaminar spinal tethering on the development of PJK in patients undergoing thoraco-lumbar deformity correction surgery for ASD.

Design and patient selection

The present retrospective cohort study was approved by the ethics committee of the Charité – Universitätsmedizin Berlin (approval number EA2/09/13). Patient consent was not required due to the retrospective design and regular clinical care. Following the introduction of the proximal translaminar tethering technique in our department in October 2019, we identified all consecutive adult patients with spinal deformity that underwent thoraco-lumbar deformity correction surgery involving more than 6 motion segments with or without proximal tethering of the upper instrumented vertebra (UIV) + 1 and UIV + 2. In all patients, a complete set of preoperative, early postoperative (≤ 3 months), and late postoperative (> 3 months) whole spine (long-standing) lateral radiographs were required.

Radiographic measurements

In order to judge PJK, the proximal junctional angle (PJA) was measured as the sagittal Cobb angle between the inferior endplate of UIV and the superior endplate of UIV + 2. As defined by Glattes et al., proximal junctional kyphosis (PJK) was considered if PJA was more than 10° larger than the preoperative measurement (Fig. 1).[7] Sagittal vertical axis (SVA), pelvic tilt (PT), pelvic incidence (PI), lumbar lordosis (LL), PI-LL mismatch, and thoracic kyphosis (TK) were evaluated as radiological measurements before and after surgery.

Tethering technique

All tethers were placed using the same technique, characterized by tethering of UIV + 1 and UIV + 2 to the rod of the instrumentation between UIV and UIV-1. In each patient, one tether and two rod connectors were used (Translace™, Medtronic Sofamor Danek, Menphis, TN, USA). Briefly, a 2mm high-speed diamond burr was used to create a translaminar perforation in the spinous processes of UIV + 1 and UIV + 2. Next, the polyester tether was attached to a suture (1 − 0 Vicryl Polyglactin 910, Ethicon, USA) and passed through the translaminar burr holes in UIV + 1, UIV + 2, and back through UIV + 1 in a figure-of-eight-shaped loop. In the last step, the tethers were passed through rod connectors that were then secured to the proximal end of the rod between UIV and UIV-1. The tension of the tether was applied manually with the goal of applying equal but not excessive force on both sides using a torque instrument (Fig. 2 and Fig. 3).

Statistical analysis

Continuous variables are presented as means with standard deviations, while categorical variables are expressed as frequencies. Pearson’s Chi square and Fischer’s exact test were used to compare baseline characteristics of the cohorts, PJK rates, revision surgery rates, total radiographic follow-up times, and time-to-PJK, as appropriate. Odds ratios (ORs) were derived from 2 × 2 contingency tables. To evaluate PJK as a time-dependent variable and compare survival rates, Kaplan-Meier analysis was conducted. Independent variables were analyzed using binary logistic regression to identify factors associated with PJK. Model fit was assessed using the Hosmer-Lemeshow goodness-of-fit test.[8] To determine the effect of the multiple covariates on survival time, a Cox proportional hazard model was employed. Statistical analysis was performed using SPSS (Inc. Version 20.0, IBM Corp., NY, SA). The level of significance was set at p < 0.05.

Patient demographics

Between October 2019 and August 2023, we identified 59 out of 71 patients (83%) that met the inclusion criteria and achieved a minimum 3-month follow-up (mean: 7.8 months, range: 3-48 months, mean age: 70.2 years, 55.9% female). Overall, the cohort consisted of 25 tethered (T) and 34 non-tethered (NT) patients. Patient demographics and surgical data regarding instrumentation length, pelvic fixation and 3-column osteotomy were comparable between both groups (Table 1).

Sagittal plane radiographic parameters

Also, between both groups no significant difference was noted in pre- and postoperative radiographic sagittal plane parameters as well as the amount of the achieved SVA and LL correction (Table 2). Additionally, the amount of postoperative change in SVA and LL was also comparable.

PJK development and revision surgery

All patients had an early follow-up at 3 months but the duration of follow-up beyond this time-point was highly variable. Therefore, time-to-PJK was calculated based on PJK rates at early (3-month) and late (>3-month) follow-up. Importantly, the overall duration of radiographic follow-up did not differ between groups with early follow-up at 16.2±5.2 weeks and 14.3±3.1 weeks (p = 0.128), and late follow-up at 37.2 ± 44.7 weeks and 35.8 ± 41.9 weeks (p=0.90) for tethered and non-tethered patients, respectively.

The univariate analysis comparing tethered and non-tethered patients for the primary outcome of postoperative PJK development across the entire duration of follow-up is summarized in Table 3. Out of all 59 patients, 18 (30.5%) developed PJK, out of which 10 (55.5%) developed PJK within the first 3 months but without difference between tethered (3/25; 12%) and non-tethered (7/34; 20.5%) patients (p=0.384). At late follow-up, however, the PJK rate was significantly higher in non-tethered (14/34; 41.1%) compared to tethered (4/25; 16%) patients (p=0.037) and overall, non-tethered patients were 3.67 times more likely to develop PJK (95%CI = 1.03-13.07). Further, Kaplan-Meier analysis suggested a significant reduction in time-dependent PJK development for tethered patients (p=0.027) (Figure 4, A). Four out of 34 (11.8%) non-tethered patients required revision surgery due to PJK, compared to 1/25 (4%) tethered patients (p = 0.289).

Predictors of PJK development

The results of the binary logistic regression are shown in Table 4 and BMI emerged as a significant independent predictor for PJK (OR=1.23, CI95% 1.04-1.46; p=0.02). The regression model did not significantly differ from a null model without the explanatory variables, indicating a good fit (p=0.06). The Cox regression hazard model indicated that tethering was associated with a reduced risk of developing PJK. However, the effect was not statistically significant (HR=0.33, 95%CI 0.08-1.31; p=0.11) (Table 5 and Figure 4, B).

PJK poses a substantial burden on patients and contributes to worsened health-related quality of life outcomes and dissatisfaction after surgery.[9] Moreover, the need for additional interventions or revision surgeries to address PJK exacerbates the already complex treatment journey, prolonging recovery and imposing financial and emotional stress. Given its common occurrence and substantial impact, understanding and mitigating PJK is important to optimize patient outcomes.

Various surgical techniques have been proposed for PJK prevention;[6, 10] these include the use of tethers at the proximal junction in various configuartions,[11, 12] prophylactic 2-level vertebroplasty,[13, 14] transverse process hooks,[15] flexible rods,[16] multilevel stabilization screws,[17] and sublaminar tapes.[18] Among these, 2-level vertebroplasty, posterior tethers and transverse process hooks are the most frequently studied techniques and show promising results.[10] Biomechanically, Bess und colleagues demonstrated through a finite element model of long instrumented spine constructs that posterior tethers, compared to segmental pedicle screws and transverse process hooks, facilitated a more gradual transition in range of movement and stress on adjacent spinal segments.[19] Many of these techniques have been traditionally implemented at the UIV + 1 level.[6] However, we have extended the application of tethers at both the UIV + 1 and UIV + 2 levels. Our analysis revealed notable differences in the rates and predictors of PJK between tethered and non-tethered patients. Univariable analysis showed that tethered patients had lower overall rates of PJK. When dichotomised based on the follow-up periods, tethers did not protect against PJK within the first 3 months postoperatively. However, beyond 3 months, tethers significantly reduced PJK incidence. Similar trends have been reported by Rodriguez-Fontan et al., who used Mersilene tape stabilisation at the UIV + 1. They observed greater change in the sagittal Cobb angle at 2 years follow-up in the control group compared to the immediate postoperative period and the 1.5 months follow-up, concluding that the protective effect becomes evident within 2 years postoperatively.[20] Additionally, Buell et al. found no significant PJK reduction with the use of tethers at 3 months but observed significantly lower rates at 6 months.[11]

The multivariable analysis indicated that, among all examined risk factors for PJK, body mass index (BMI) emerged as the only significant independent predictor of PJK risk. However, when evaluating the time-to-development of PJK, more nuanced insights were obtained. The Kaplan-Meier survivorship analysis demonstrated that the use of tethers resulted in a higher probability of remaining PJK-free in the weeks following surgery. Although not statistically significant, the Cox regression analysis demonstrated that the use of tether resulted in a lower cumulative risk of developing PJK. This discrepancy between odd ratios and time-dependant analysis underscore the temporal dimension of risk, which is crucial for a comprehensive understanding of PJK development.

In this study, the correlation between patient symptoms and clinical outcomes with radiographic findings of PJK was not assessed. Instead, the rate of revision surgery was used as an indirect indicator of the severity of symptoms or radiographic findings necessitating surgical intervention. We reported an overall incidence of surgical PJK of 8.5%, which is comparable to the 6.7% incidence reported in a meta-analysis conducted by Luo et al.[21] Additionally, consistent with the findings of Buell et al.[22], we observed lower revision rates with the use of tethers; however, the difference did not reach statistical significance.

The limitations of this study include its retrospective design. However, no other surgical techniques to address PJK, which may confound the outcomes, were utilised. Furthermore, the baseline patient characteristics, surgical data, pre- and postoperative sagittal radiographic measurements, as well as the degree of correction were comparable between the two groups. Another limitation is the relatively short follow-up periods; the average long-term follow-up in this study ranged between 35–37 weeks, thus constraining the assessment of long-term outcomes associated with the use of tethers. Nevertheless, the literature indicates that most PJK occurs within the first 3 months postoperatively. [23, 24] For example, Yagi et al., demonstrated in a study with a minimum of 5-year follow-up, that 76% of PJK occurred within the first 12 weeks postoperatively, and no patient demonstrated PJK after 5 years of follow-up. [24] In addition, the average PJ angle increase at 12 weeks postoperatively accounted for 53% of the total PJ angle increase at final follow-up. In our study, more than half of the patients (55%) who developed PJK, did so in the first 3 months after the surgery.

Use of polyester tethers at the UIV + 1 and UIV + 2 in patients undergoing thoraco-lumbar deformity correction significantly reduced the overall PJK incidence and increased the PJK-free probability following surgery. The association between translaminar tether augmentation and surgical revision rates due to PJK still remains unclear. Prospective long-term observation is needed to determine the course of PJK and its effect on clinical outcome over time.

The authors have no conflicts of interest to declare that are relevant to the content of this article. No funding was received to assist with the preparation of this manuscript. The study was approved by the ethics committee (EA4/093/13)

Author Contribution

TAS* : Conceptualisation, methodology, data curation, writing – original draft, project administrationAA* : Methodology, data curation, statistics, writing – original draftEV: Data curationLF: Prepared figuresJA: Data curationDT: Data curationAF: StatisticsSB: MethodologyNH: Conceptualisation, methodology, writing – original draft, project administrationPV: Conceptualisation, supervisionAll authors reviewed the manuscript* These two authors contributed equally to this work.

Data Availability

All collected personal and medical data are coded and recorded by the rules of good clinical practice. Data is provided within the manuscript or supplementary information files

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Table 1. Patient demographics and surgical data^a
	Non-tethered (NT, n = 34)	Tethered (T, n = 25)	P^b
Age at surgery (years)	70.44 ± 9.19	69.92 ± 11.01	0.424
Gender (female/male)	15/19	11/14	0.992
Body mass index (kg/m²)	27.64 ± 5.59	28.78 ± 7.39	0.248
Number of instrumented vertebrae	10.17 ± 3.31	10.56 ± 2.52	0.307
Pelvic fixation (yes/no)	33/1	24/1	0.158
3-column osteotomy (yes/no)	31/3	23/2	0.91
^aValues are expressed as the mean ± standard deviation or frequency for continuous and categorical variables, respectively. ^bComparison of the two groups analyzed with Pearson’s chi square or Fischer’s exact test

Table 2. Sagittal plane radiographic parameters^a
	Non-tethered (NT, n = 34)	Tethered (T, n = 25)	P^b
Preoperative
Sagittal vertical axis (cm)	8.62 ± 5.7	10.14 ± 3.27	0.119
Pelvic tilt (°)	27.33 ± 8.15	23.82 ± 8.89	0.064
Pelvic incidence (°)	68.81 ± 11.72	63.2 ± 14.5	0.12
Lumbar lordosis (°)	27.9 ± 12.63	28.6 ± 14.84	0.186
PI-LL mismatch (°)	40.9 ± 15.36	34.6 ± 20.44	0.101
Thoracic kyphosis (°)	37.67 ± 17.14	34.44 ± 19.55	0.256
Postoperative
Sagittal vertical axis (cm)	4.26 ± 2.42	4.93 ± 2.39	0.147
Pelvic tilt (°)	25.68 ± 8.82	23.76 ± 7.1	0.361
Pelvic incidence (°)	67.66 ± 12.92	63.36 ± 15.27	0.131
Lumbar lordosis (°)	43.65 ± 14.18	47.16 ± 10.19	0.138
PI-LL mismatch (°)	23.3 ± 17.62	16.2 ± 17.07	0.062
Thoracic kyphosis (°)	39.16 ± 15.89	44.24 ± 16.41	0.122
Amount of correction
Sagittal vertical axis (cm)	4.36 ± 5.38	5.2 ± 3.46	0.234
Lumbar lordosis (°)	15.28 ± 13.53	18.56 ± 15.75	0.203
PI; pelvic incidence, LL; lumbar lordosis. ^aValues are expressed as the mean ± standard deviation for continuous variables. ^bComparison of the two groups analyzed with Fischer’s exact test.

Table 3. Postoperative rates of PJK, revision surgery, and change in proximal junctional angle (PJA) at late follow up (> 3 months).
	Non-tethered (NT, n = 34)	Tethered (T, n = 25)	P^a
3-months PJK (%)^a	20.5	12	0.384 (χ 2 = 0.754)
Yes	7	3
No	27	22
>3-months PJK (%)^a	41.1	16	0.037 (χ 2 = 4,307)
Yes	14	4
No	20	21
Revision for PJK (%)^a	11.8	4	0.289 (χ 2 = 1.119)
Yes	4	1
No	30	24
Change in PJA (°)^b	5.97 ± 11.04	2.26 ± 9.7	0.088
^aPearson’s chi square test with 2 x 2 contingency table. ^bAnalyzed using Fischer’s exact test.

Table 4. Multivariable analysis of patients dichotomized based on development of PJK on late follow-up (beyond 3 months) after the surgery^a
	OR (95% CI)	P
Age at surgery	0.94 (0.87-1.02)	0.13
Female gender	1.75 (0.41-7.52)	0.45
Body mass index	1.23 (1.04-1.46)	0.02
Number of instrumented vertebrae	1.11 (0.89-1.37)	0.35
Pelvic fixation	0.65 (0.03-15.59)	0.79
3-column osteotomy	1.82 (0.24-13.56)	0.56
Use of polyester tether	0.18 (0.02-1.32)	0.09
Preoperative sagittal vertical axis	0.95 (0.81-1.12)	0.52
Amount of correction
Sagittal vertical axis	0.95 (0.93-1.02)	0.29
Lumbar lordosis	1.06 (0.99-1.14)	0.08
CI; confidence interval, OR; odds ratio. ^aExplanatory variables were entered in a stepwise, multivariable model using binary logistic regression

Table 5. Cox proportional hazard regression analysis for development of PJK
	HR (95% CI)	P
Age at surgery	0.97 (0.92-1.03)	0.3
Female gender	1.17 (0.4-3.41)	0.78
Body mass index	1.03 (0.96-1.09)	0.42
Number of instrumented vertebrae	0.99 (0.84-1.17)	0.91
Pelvic fixation	1.09 (0.13-9.37)	0.94
3-column osteotomy	1.31 (0.31-5.44)	0.72
Use of polyester tether	0.33 (0.08-1.31)	0.11
Preoperative sagittal vertical axis	1.00 (0.89-1.12)	0.99
Amount of correction
Sagittal vertical axis	0.99 (0.96-1.03)	0.72
Lumbar lordosis	1.04 (0.99-1.08)	0.09
CI; confidence interval, HR; hazard ratio.

No competing interests reported.

Standardized translaminar spinal tethering to prevent proximal junctional kyphosis in adult spinal deformity correction surgery

Status:

Version 1

Abstract

Figures

INTRODUCTION

METHODS

Design and patient selection

Radiographic measurements

Tethering technique

Statistical analysis

RESULTS

DISCUSSION

Conclusion

Declarations

Author Contribution

Data Availability

References

Tables

Additional Declarations

Status:

Version 1