How to reconstruct the lordosis of cervical spine in patients with Hirayama disease? A finite element analysis of biomechanical changes focusing on adjacent segments after anterior cervical discectomy and fusion

Lu et al. Journal of Orthopaedic Surgery and Research https://doi.org/10.1186/s13018-022-02984-y (2022) 17:101 Open Access RESEARCH ARTICLE How to reconstruct the lordosis of cervical spine in patients with Hirayama disease? A finite element analysis of biomechanical changes focusing on adjacent segments after anterior cervical discectomy and fusion Xiao Lu†, Fei Zou†, Feizhou Lu, Xiaosheng Ma, Xinlei Xia and Jianyuan Jiang* Abstract Purpose: To compare the biomechanical changes of adjacent segments between patients with Hirayama disease and non-pathological people after anterior cervical discectomy and fusion (ACDF) operation, and to explore the optimal degree of local lordosis reconstruction during surgery. Methods: A young male volunteer was recruited to establish a three-dimensional finite element model of the lower cervical spine based on the CT data. By adjusting the bony structures and simulating the operation process, the models of non-pathological individuals before and after ACDF, patients with Hirayama disease before and after ACDF, and different local lordosis angles were established. Then, the postoperative range of motion (RoM) and stress of the adjacent segments under flexion, extension, left bending, right bending, left rotation and right rotation were recorded and compared. Results: The RoM and stress of all segments of lower cervical spine in patients with Hirayama disease are higher than those in non-pathological individual, and this trend still exists after ACDF surgery. When the local lordosis angle is under physiological conditions, the RoM and stress of the adjacent segments are minimum. Conclusion: Compared with non-pathological people, Hirayama disease patients have differences in cervical biomechanics, which may lead to cervical hypermobility and overload. After ACDF, the possibility of adjacent segments degeneration is greater than that of non-pathological people. When the operation maintains the physiological local lordosis angle, it can slow down the degeneration. Keywords: Hirayama disease, Finite element analysis, ACDF, Biomechanics, Degeneration *Correspondence: † Xiao Lu and Fei Zou have contributed equally to this work Department of Orthopedics, Huashan Hospital, Fudan University, No. 12, Middle Wulumuqi Road, Jing’an District, Shanghai 200040, China Introduction Hirayama disease, also known as juvenile muscular atrophy of distal upper extremity, is a disease characterized by asymmetrical atrophy of the intrinsic muscles of the hand and forearm muscles. It occurs frequently in adolescents, with an average age of 15–20 years old [1, 2]. Its clinical manifestations are asymmetrical muscle atrophy and weakness in the distal part of the unilateral upper © The Author(s) 2022. 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The Creative Commons Public Domain Dedication waiver (http://creativeco mmons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Lu et al. Journal of Orthopaedic Surgery and Research (2022) 17:101 limb, with tremor and cold paralysis, no sensory disturbance and pyramidal tract damage [3, 4]. Hirayama disease mainly affects the hand function of teenagers, resulting in the decline or even loss of patients’ ability to work, which brings a heavy burden to individuals, families and society. In the treatment of Hirayama disease, a neck brace can be worn at an early stage, but for those who cannot adhere to wearing it or whose disease course is rapidly progressing, anterior cervical discectomy and fusion (ACDF) surgery is considered one of the effective treatments. The purpose of the operation is to reconstruct the physiological curvature of the cervical spine, reduce the range of motion (RoM) of the cervical spine, and prevent the forward compression of the spinal cord in the flexion position. Both imaging and clinical scores have proved its effectiveness [5–7]. The bony structure of the cervical spine in Hirayama disease is different from that in non-pathological people, and the curvature of the cervical spine becomes straight or kyphosis [8, 9]. We found that when the cervical curvature was reconstructed to normal physiological curvature during ACDF, the upper adjacent segment would have compensatory kyphosis, so how to reconstruct the cervical curvature of Hirayama disease patients remains unclear. In this study, eight three-dimensional (3D) finite element models of non-pathological lower cervical spine (NLCS), NLCS + C4–6 ACDF, NLCS + C5–7 ACDF, lower cervical spine of Hirayama disease (LCSHD), LCSHD + C4–6 ACDF, LCSHD + C5–7 ACDF, LCSHD + C4–6 ACDF + C4–6 posterior wall angle (PWA) 0°, and LCSHD + C4–6 ACDF + C4–6 PWA 5° were established by 3D finite element analysis, and the biomechanical differences of adjacent segments of intervertebral discs between non-pathological people and patients with Hirayama disease after ACDF were compared. The main purpose of this study was to compare the biomechanical changes of adjacent segments in Hirayama disease patients and non-pathological controls by 3D finite element analysis. Then, we explored how to reconstruct the cervical curvature of Hirayama disease patients through ACDF to minimize the impact on adjacent segments. Materials and methods Establishment of 3D finite element model A healthy male volunteer, aged 24 years, with a height of 170 cm and a weight of 60 kg, was recruited. There was no previous history of neck disease. 64 slice CT (Siemen Company; Germany) was performed in the CT room of medical imaging center, Huashan Hospital, Fudan University (120 kV, 125 mA, scanning thickness 0.625 mm, Page 2 of 10 range C2–T2). The CT scan data were exported and saved in DICOM format, and a total of 260 images were obtained. And the project was approved by the ethics committee of Huashan Hospital (KY-2019-546). The CT data were imported into Mimics 21.0 (Materialise, Belgium) software to segment each vertebral body and establish the non-pathological lower cervical spine model of C3–C7. Then, the file was imported into Geomagic wrap 2017 (Geomagic company, USA) for polishing, smoothing and other pr (...truncated)