Elsevier

The Spine Journal

Volume 18, Issue 10, October 2018, Pages 1779-1786
The Spine Journal

Clinical Study
Effect of posterior instrumented fusion on three-dimensional volumetric growth of cervical ossification of the posterior longitudinal ligament: a multiple regression analysis

https://doi.org/10.1016/j.spinee.2018.03.002Get rights and content

Abstract

Background Context

Despite the fact that ossification of posterior longitudinal ligament (OPLL) is a three-dimensional disease, conventional studies have focused mainly on a two-dimensional measurement, and it is difficult to accurately determine the volume of OPLL growth and analyze the factors affecting OPLL growth after posterior decompression (laminoplasty or laminectomy and fusion).

Purpose

The present study aimed to investigate the factors affecting OPLL volume growth using a three-dimensional measurement.

Study Design/Setting

This was a retrospective case study.

Patient Sample

Eighty-three patients with cervical OPLL who were diagnosed as having multilevel cervical OPLL of more than three levels on cervical computed tomography (CT) scans were retrospectively reviewed from June 1, 1998, to December 31, 2015.

Outcome Measures

The OPLL volume from the C1 vertebrae to the C7 vertebrae was measured on preoperative and the most recent follow-up CT scans.

Methods

Eighty-three patients were retrospectively examined for age, gender, body mass index, hypertension, diabetes, type of OPLL, surgical method, preoperative cervical curvature, and preoperative and postoperative cervical range of motion. Preoperative cervical CT and the most recent follow-up cervical CT scans were converted to Digital Imaging and Communications in Medicine data, and the OPLL volume was three-dimensionally measured using the Mimics program (Materialise, Leuven, Belgium). The OPLL volume growth was analyzed using univariate and multivariate analyses.

Results

The average follow-up period was 32.36 (±23.39) months. Patients' mean age was 54.92 (±8.21) years. In univariate analysis, younger age (p=.037) and laminoplasty (p=.012) were significantly associated with a higher mean annual growth rate of OPLL (%/y). In multivariate analysis, only laminoplasty (p=.027) was significantly associated with a higher mean annual growth rate of OPLL (%/y). The mean annual growth rate of OPLL was about seven times faster with laminoplasty (8.00±13.06%/y) than with laminectomy and fusion (1.16±9.23%/y).

Conclusions

Posterior instrumented fusion has the effect of reducing OPLL growth rate compared with motion-preserving laminoplasty. Patients' age and the surgical method need to be considered in surgically managing the multilevel OPLL.

Introduction

Evidence & Methods

Laminoplasty and laminectomy with fusion are two options for the surgical treatment of OPLL. The authors compared the two in regards to OPLL growth following surgery using 3D CT.

They found that laminectomy and fusion appears to result in less progression of growth than open-door laminoplasty.

The limitations are discussed by the authors; the unclear clinical implications being most important.

Ossification of the posterior longitudinal ligament (OPLL) is a condition caused by abnormal calcification and growth of the posterior longitudinal ligament. The growth of OPLL sometimes causes narrowing of the spinal canal and cord compression, which may require surgical intervention [1], [2]. Additionally, the growth of OPLL after decompressive operation has been considered a main cause of delayed reoperation 2 years after the index operation [3], [4], [5]. Therefore, it is clinically important to understand factors affecting OPLL volume growth to better counsel patients and to determine the optimal surgical method. In previous studies, the surgical intervention, a young age, the type of OPLL, and the surgical methods have been indicated as factors for OPLL growth [6], [7], [8], [9], [10]. However, these studies used two-dimensional measurements on plain radiographs and plain computed tomography (CT) scans, making it difficult to demonstrate the total volume and volumetric growth of OPLL. In addition, OPLL gradually increased over a long period, and sometimes OPLL increased by a small amount. Thus, it was difficult to quantify the exact growth volume of OPLL and to analyze various factors affecting OPLL growth. Recently, studies on the measurement of OPLL volume using three-dimensional methods have been introduced [11], [12], [13]. However, studies on factors that affect volumetric growth of OPLL are still inadequate [11], [12], [13]. No previous reports have performed multivariate regression to identify factors exclusively associated with volumetric growth of OPLL. Therefore, in the present study, we measured OPLL growth using a three-dimensional measurement and analyzed the factors affecting OPLL growth after posterior decompressive operation. Moreover, we compared the growth rate between the surgical levels and the non-surgical levels and determined whether instrumented fusion reduced OPLL growth.

Section snippets

Materials and methods

The present study was approved by the institutional review board (IRB) of Yonsei University Severance Hospital (IRB number 4-2014-0529). We performed a retrospective analysis of patients with multilevel cervical OPLL (more than three levels) identified on cervical CT scans. We included patients surgically treated with laminoplasty (LP) or laminectomy and fusion (LF) at our institution from June 1, 1998, to December 31, 2015 by two senior authors (HCS and YH), with a minimum follow-up of 2

Patients' demographic characteristics

Overall, we found a total of 282 patients with multilevel cervical OPLL, with 83 patients meeting the inclusion criteria. We excluded a total of 199 patients: 13 patients with trauma and fracture or tumor, 85 patients who underwent anterior cervical surgery, 17 patients with previous history of cervical operation, 15 patients who underwent circumferential fusion, and 69 patients who were lost to follow-up. The mean follow-up period was 32.36 (±23.39) months, and patients' mean age was 54.92

Discussion

Previous literatures have compared LF and LP for OPLL growth. Ota et al. [17] reported that the progression of the thickness of OPLL was significantly smaller in the posterior decompression with instrumented fusion group (−0.1±0.4 mm) than in the LP group (0.6±0.7 mm, p=.0002). Lee et al. [20] found that OPLL growth was more frequently observed in LP than in LF (45.5% vs. 30.0%). In the study by Katsumi et al. [11], 19 LF groups and 22 LP groups were compared using the three-dimensional

Limitations of the study

The present study has some limitations. First, as described in the previous three-dimensional studies [11], [28], [29], the three-dimensional measurement process is semi-automatic, resulting in interobserver and intraobserver errors. However, previous studies have shown high intraobserver and interobserver reliability in three-dimensional measurements [29], [30]. It is also considered a more accurate method because it is fundamentally measured in several precise axial CT cuts rather than

Conclusions

The mean annual growth rate of OPLL was about seven times faster in the LP group (8.00±13.06%/y) than in the LF group (1.16±9.23%/y) in the present study. We conclude that posterior instrumented fusion has the effect of reducing OPLL growth rate compared with motion-preserving LP, which was similar to the results of the previous studies [11], [17], [20]. Patients' age and the surgical method need to be considered in surgically managing the multilevel OPLL.

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      After removal of duplicates and abstract screening, 73 articles were identified for full text assessment. Finally, 30 cohort studies involving 2038 patients met the inclusion criteria (Figure 1).6,7,9-36 Six studies were prospective cohort studies, and the remaining studies were retrospective cohort studies.

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      Therefore, a larger prospective study is needed to verify our findings. Second, a longer follow-up period will be needed to observe the effect of ACAF on OPLL growth, although investigators have previously reported that fusion surgery can suppress OPLL growth or even decrease OPLL mass, which is in accord with our clinical observations [21,36,37]. Third, the hoisting distance for the VOC is controllable in ACAF, and our study established the standard for hoisting distance.

    • Extended Laminoplasty for Ossification of Posterior Longitudinal Ligament Involving the C2 Segment

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      When considering postoperative OPLL progression, cervical fixation with fusion seemed to be more suitable. However, as reported in previous studies, the incidence of late neurologic deterioration after the laminoplasty was rare,15,16 and when compared with laminoplasty, implants of bilateral C2 pedicle screws, C1/2 and C2/3 transarticular screws were of higher risk of vertebral artery injury. In this study, a lower JOA score before the operation in Group A should be contributed to prolonged extent of cord compression when compared with that in Group B or Group C. However, comparable neurologic RR and similar distribution of its classification among the 3 groups at the final visit (Table 2) suggested that extended laminoplasty up to the C2 segment could provide satisfactory neurologic improvement for cases with C2 OPLL.17

    • Postoperative Progression of Cervical Ossification of Posterior Longitudinal Ligament: A Systematic Review

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      Ota et al.’s study30 showed that progression of the thickness of OPLL in the fusion surgery group (–0.1 ± 0.4 mm) was significantly smaller than in the laminoplasty group (0.6 ± 0.7 mm). Lee et al.35 investigated the effect of posterior instrumented fusion on 3D volumetric growth of ossification in 83 cases of multilevel OPLL. The research found that the mean annual growth rate of OPLL was about 7 times faster with laminoplasty (8.00 ± 13.06%/year) than with laminectomy and fusion (1.16 ± 9.23%/year), which indicated that posterior instrumented fusion has the effect of reducing OPLL growth rate more than does laminoplasty.

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    FDA device/drug status: Not applicable.

    Author disclosures: JJL: Nothing to disclose. DAS: Nothing to disclose. SY: Nothing to disclose. KNK: Nothing to disclose. DHY: Nothing to disclose. HCS: Nothing to disclose. YH: Nothing to disclose.

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