Clinical and radiological outcomes of single-level cervical disc arthroplasty in the patients with preoperative reversible kyphosis: A matched cohort study

Highlights

• Patients with preoperative reversible kyphosis and lordosis were matched.

• Both groups achieved satisfactory and comparable clinical outcomes.

• The cervical alignment of RK group was inferior to that of lordosis group.

• More HO formation occurred in RK group.

• We did not recommend CDA to the patients with preoperative RK.

Abstract

Objective

The performance of cervical disc arthroplasty (CDA) in the spine with malalignment was unclear. The purpose of the study was to report the clinical and radiological outcomes of single-level CDA in the patients with preoperative reversible kyphosis (RK) and compare these results with a matched cohort of preoperative lordosis.

Patients and Methods

From 2014 to 2018, 36 patients with preoperative RK were matched with 229 patients with preoperative lordosis. The Japanese Orthopedic Association score, Neck Disability Index, Visual Analog Scale were used to evaluate clinical outcomes. Radiological evaluations included range of motion (ROM), C2−7 Cobb angle, shell angle (SA) at surgical level, functional spinal unit (FSU) angle and heterotopic ossification (HO).

Results

The mean follow-up was 40.1 months. Both groups achieved significant improvements in clinical outcomes without significant intergroup differences. Before surgery, lordosis group had significantly greater C2−7 angle (9.5° vs -8.4°), SA (1.6° vs -3.7°), and FSU (2.9° vs -3.7°). After surgery, RK group experienced significant improvements in C2−7 angle and SA compared with preoperative data. In lordosis group, C2−7 angle, SA, and FSU were maintained. At the last follow-up, the intergroup difference of C2−7 angle, SA, and FSU remained significant. ROMs were preserved in both groups. The ROM of RK group was slightly lower than that of lordosis group but failing to reach a significance. Eleven patients in lordosis group and 21 patients in RK group developed HO (P = 0.127). There was a significant greater incidence of high-grade HO (grade Ⅲ, Ⅳ) in RK group (33.3 % vs 11.1 %, P = 0.034).

Conclusion

Both groups achieved satisfactory and comparable clinical outcomes after CDA. Despite the remarkable improvements compared with preoperative values, the cervical alignment of RK group was still significantly inferior to that of lordosis group. More HO formation occurred in RK group. Based on these results, we did not recommend CDA to the patients with preoperative RK.

Introduction

Generally, lordosis has been considered as the normal and physiological posture of cervical spine, as opposed to the kyphosis that is regarded as the abnormal deformity or morbid status [1]. However, many authors hold a different opinion that cervical kyphosis might naturally occur in asymptomatic individuals. Yu et al. [2] reported that lordosis only account for 28.3 % in the asymptomatic population while 21.7 % normal people had the kyphotic alignment. In a cross-sectional radiographic study with 1026 asymptomatic subjects [3], cervical kyphosis was found in 26.3 % participants, and 16.7 % of the kyphotic individuals had the irreducible kyphosis. Although the prevalence and degree of normal cervical alignment is currently debated in the literature, most surgeons reach a unanimous view on the restoration of a lordotic spinal curvature when it comes to surgical decision-making in front of a kyphotic cervical spine.

In recent decades, cervical disc arthroplasty (CDA) has been presented as a promising new technology to treat patients with refractory cervical disc degenerative disease. By preserving of the mobility of the implanted segment and decreasing the biomechanical stress on adjacent levels, CDA could theoretically slow down adjacent segment degeneration. In several meta-analyses and randomized controlled studies with long-term follow-up, CDA achieved equivalent or superior clinical and radiological outcomes compared with anterior cervical discectomy and fusion (ACDF) [[4], [5], [6], [7]]. However, due to relatively strict indications and reasonable prudence towards this new surgical technique, most studies reported the application of CDA in cervical spine with lordosis. The performance of CDA in patients with malalignment was unclear.

On the one hand, many surgeons regarded preoperative malalignment as a contraindication for CDA surgery [8], because the cervical disc prostheses lacked anterior column support, and the kyphotic segmental alignment was widely reported after insertion with BRYAN® Cervical Disc (Medtronic, Sofamor Danek, Memphis) [9,10]. On the other hand, a few studies [4,[11], [12], [13], [14]] indicated that CDA had the potential to improve or even reconstruct cervical alignment to some extent. Chen et al. found that CDA might be a possible option for the single-level cervical disc degenerative disease with flexible kyphosis [12,14]. But to our knowledge, the supporting evidence for the latter view was scarce.

The purpose of this study was to report the clinical and radiological outcomes of single-level CDA in the patients with preoperative reversible kyphosis (RK), and to compare these results with those of a matched cohort with preoperative lordosis. In this study, special attention was paid to the change of cervical alignment and postoperative complications.