Proposed Classification System of Radiographic Bony 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. Radiographic bone changes are a common observation around hip and knee arthroplasty as well as CDR prostheses. Historically, classification systems have been common tools used to assist communication and perioperative evaluation, as well as to provide guidance for potential treatment options. A classification system with a common nomenclature for radiographic observations of periprosthetic bone changes following CDR is proposed.

Methods:
A panel of experts was assembled for the purpose of creating a classification system for radiographic observations following CDR. Using serial radiographs from patients, a classification system has been proposed to aid in reproducibly and consistently identifying bony changes and assessing CDR device radiographic appearance. Subdividing the superior and inferior vertebral bodies into 3 equal sections (anterior, middle, posterior), observed bone loss is recorded. Bone loss categories of interest include endplate rounding, cystic erosion adjacent to the endplate with diffuse and/or sclerotic margins, and cystic erosion not adjacent to the endplate. Serial radiographs are important in determining if the bone loss is progressive and it is informative to estimate the severity of bone loss measured by the percentage of the endplate involved. Additional bony changes that may be relevant in the assessment of the radiographic appearance and device performance include progressive or non-progressive radiolucent lines (with and without sclerotic margins), as well as heterotopic ossification (HO), using the McAfee classification system. Other important radiographic observations include loss of core implant height and the presence or absence of device migration, subsidence, and olisthesis. Several iterations were conducted involving radiographs from 34 patients with 44 implants from 7 implant systems to refine the categories and usability of the classification system.

Results:
To assess the classification system, serial radiographs from 19 patients implanted with 25 CDRs from 7 different implant systems were evaluated. The implant in situ duration of these implants ranged between 3 months to 7 years. This provided a broad range of radiographic scenarios for the assessment. The serial radiographs were reviewed by 6 investigators including clinicians and scientists experienced in CDR or appendicular skeleton joint replacement to develop an accurate and reproducible classification scheme. The classification system that emerged had improved concordance among the participating investigators, with inferior anterior and posterior HO, inferior medial, superior medial, inferior posterior bone loss, and loss of core implant height all having agreement >90%. Next steps include assessing reliability with a broad group of clinicians and scientists, using serial radiographs from a significant number of patients, to confirm the proposed classification scheme.

Conclusions:
A standardized nomenclature for bony changes following CDR will be useful to facilitate accurate and reproducible scientific communications regarding the clinical outcomes of this procedure. It is also an important step in supporting clinical management discussions regarding CDR. The novel system proposed here demonstrated good concordance among experienced investigators in this field and represents an important advancement.