Proposed Classification System of Radiographic Bone Changes After Cervical Disc Replacement

INTRODUCTION: Cervical Disc Replacement (CDR) is an increasingly utilized procedure to address cervical degenerative conditions, as an alternative to discectomy and fusion, for the purpose of preserving natural segmental motion. METHODS: Using serial radiographs from patients, a panel of experts assembled for the purpose of creating a classification system to aid in reproducibly and consistently identifying boney changes and assessing CDR device radiographic appearance. Subdividing the superior and inferior vertebral bodies into 3 equal sections, observed bone loss such as endplate rounding, cystic erosion adjacent to the endplate, and cystic erosion not adjacent to the endplate, is recorded. Determining if bone loss is progressive and estimating severity of bone loss (measured by the percentage of end plate involved) is recorded. Additional relevant boney changes and device observations include radiolucent lines, heterotopic ossification, loss of core implant height, and presence of device migration, subsidence, and olisthesis. RESULTS: Serial radiographs from 26 patients implanted with a variety of CDR products were assessed by 6 investigators including clinicians and scientists experienced in CDR or appendicular skeleton joint replacement. After several iterations, a classification system emerged that had improved concordance among the participating investigators. Next steps include assessing reliability with a broad group of clinicians, using serial radiographs from a significant number of patients, to confirm the proposed classification scheme. CONCLUSIONS: A standardized nomenclature for boney changes following CDR will facilitate accurate and reproducible scientific communications regarding the clinical outcomes of this procedure. The novel system proposed demonstrated good concordance among experienced investigators in this field and represents an important advancement.