Background Periprosthetic bone loss is a common observation following arthroplasty. Recognizing and understanding the nature of bone loss is vital as it determines the subsequent performance of the device and the overall outcome. Despite its significance, the term “bone loss” is often misused to describe inflammatory osteolysis, a complication with vastly different clinical outcomes and treatment plans. Therefore, the goal of this review was to report major findings related to vertebral radiographic bone changes around cervical disc replacements, mitigate discrepancies in clinical reports by introducing uniform terminology to the field, and establish a precedence that can be used to identify the important nuances between these distinct complications. Methods A systematic review of the literature was conducted following PRISMA guidelines, using the keywords “cervical,” “disc replacement,” “osteolysis,” “bone loss,” “radiograph,” and “complications.” A total of 23 articles met the inclusion criteria with the majority being retrospective or case reports. Results Fourteen studies reported periprosthetic osteolysis in a total of 46 patients with onset ranging from 15–96 months after the index procedure. Reported causes included: metal hypersensitivity, infection, mechanical failure, and wear debris. Osteolysis was generally progressive and led to reoperation. Nine articles reported non-inflammatory bone loss in 527 patients (52.5%), typically within 3–6 months following implantation. The reported causes included: micromotion, stress shielding, and interrupted blood supply. With one exception, bone loss was reported to be non-progressive and had no effect on clinical outcome measures. Conclusions Non-progressive, early onset bone loss is a common finding after CDA and typically does not affect the reported short-term pain scores or lead to early revision. By contrast, osteolysis was less common, presenting more than a year post-operative and often accompanied by additional complications, leading to revision surgery. A greater understanding of the clinical significance is limited by the lack of long-term studies, inconsistent terminology, and infrequent use of histology and explant analyses. Uniform reporting and adoption of consistent terminology can mitigate some of these limitations. Executing these actionable items is critical to assess device performance and the risk of revision. Level of Evidence IV Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.

Background: Reviews of total disc arthroplasty (TDA) performance have focused on prospective randomized controlled trials (RCTs), excluding potentially important clinical information reported by others. The goal of the present study was to perform a comprehensive review, including both RCTs and non-randomized cohorts with more than five years of clinical outcome. We further explored the differences in outcome between prospective RCT and non-randomized, including retrospective studies. Methods: A systematic literature review was performed following PRISMA guidelines. Inclusion criteria were: clinical follow-up ≥ 5 years with quantitative clinical and radiographic outcome. All studies that met these criteria, including retrospective and non-randomized studies, were included, for a total of 62 studies. As anterior cervical discectomies and fusion (ACDF) was included as a control group in the majority of the studies, comparisons between TDA and ACDF were conducted. Results: Overall, there was a statistically significant difference between the rates of secondary surgeries reported for prospective RCTs and all other studies, with reoperation rates of 5.4% for prospective RCT studies v. 7.5% in all others (P<0.01). Including all studies, the reoperation rate for TDA patients was 5.6% and for fusion patients (included as control groups), 7.8%, (P=0.06). Overall, the reported incidence of adjacent segment degeneration was 26.2% in TDA patients and 43.9% in fusion patients (P<0.001). Conclusions: These findings demonstrated the need for including all available data to assess the current outcomes of cervical disc arthroplasty and account for potential biases.

Total disc replacements utilize textured coatings to maximize bony ongrowth. However, the contribution of direct bony attachment to overall fixation for total disc replacements has not been reported. The goal of the present study was to document the extent of bony attachment to the surfaces of two clinically functional total disc replacements that were securely fixed at the time of revision. Two metal‐and‐polymeric disc replacements, one cervical and one lumbar, were evaluated following surgical retrieval. The cervical device was retrieved at 8 months and the lumbar device at 28 months post‐operative. Both devices were reported well‐fixed at the time of removal, with large bone masses attached to one endplate of each device. Visual inspections, non‐destructive gravimetric measurements, and surface metrology were performed to assess fixation. These inspections suggested that both devices had been fixed at the time of removal with little in vivo mechanical damage, as surgical extraction damage was noted on both devices and provided imaging showed a lack of device migration. Devices were then embedded and sectioned to evaluate the bone‐implant interface. High resolution photographs and contact microradiographs were taken to assess bony attachment. In contrast to initial analysis, these images revealed radiolucent gaps between the endplates and bone masses. Little direct contact between the bone and endplate surface was identified and the original surgical cuts were still visible. Both devices were clinically fixed at the time of removal and neither had complications associated with loosening. However, osseointegration was minimal in one of the devices and altogether absent from the other. The findings of the present study suggest that other factors may influence overall clinical fixation such as the surgical preparation of the vertebral bone or the surface roughness of the treated endplates. Despite the limitations of the present study, this information is unique to the current total disc replacement literature and the ongrowth and fixation of devices should be considered as a topic for future investigation.