Atypical Heterotopic Bone Formation Rear to the Functioning Cervical Artificial Disc Prosthesis Causing Cervical Spondylotic Myelopathy

Abstract

Although heterotopic ossification (HO) might occur in a substantial proportion of cervical disc arthroplasty-switched spinal segments, it is predominantly discovered at the anterior vertebral edges of the treated interspace. Herein, we present the case of a 63-year-old woman who presented with clinical signs of myelopathy almost 5 years after the implantation of a Mobi-C disc prosthesis for C6-7 soft disc herniation. As shown by magnetic resonance imaging and computed tomography, spinal cord compression and a consequent signal change inside the cord were attributed to bony spurs from HO posterior to the still-moving prosthesis. Initial full posterior decompression through C6-7 bilateral laminectomy added to posterior stabilization almost fully relieved the patient’s functional and sensory changes from myelopathy. However, the device, as well as the ectopic bone deposits, had to be removed, and switching to anterior arthrodesis was necessary due to the imminent aggravation and progression of cervical kyphotic curvature from the still-functioning device. To the authors’ knowledge, such extensive bone accumulation posterior to a functional Mobi-C cervical prosthesis causing myelopathy has not yet been reported in the literature. Conversion to solid fusion would be preferred to posterior decompression for the sake of maintaining cervical curvature.