Bone loss or osteolysis after cervical disc arthroplasty? A systematic review on clinical differentiation.

PURPOSE: To differentiate between bone loss and osteolysis following cervical disc arthroplasty (CDA), elucidate their distinct pathophysiological mechanisms, and guide clinical management. METHODS: A PRISMA-guided systematic search of PubMed, Web of Science and Embase databases identified 41 articles. Evidence synthesis was stratified by study quality, prosthesis type, and outcome category. Core quantitative findings on incidence, onset, and prognosis were derived exclusively from high- and moderate-quality cohort studies, while case series and reports were used to describe rare or severe phenotypes. RESULTS: Analysis of high- and moderate-quality cohort studies revealed two distinct clinical entities with opposing trajectories. Bone loss (20 studies) occurs as an early, self-limiting phenomenon within three to 12 months postoperatively, with a high incidence (52.4%-79.5%). Bone loss does not compromise mid- to long-term clinical outcomes or necessitate revision surgery. In contrast, osteolysis (21 studies) is a late-onset, progressive pathological process with a lower incidence (13.4%-35.9%) and typically emerges more than 13 months after surgery and peaks around three years later. Osteolysis is frequently associated with complications such as implant subsidence and heterotopic ossification, and a significant proportion of symptomatic cases require revision surgery. CONCLUSIONS: Bone loss is an early, non-progressive and self-limiting phase of adaptive bone remodelling with benign clinical implications. Conversely, osteolysis is a delayed, progressive, inflammatory, osteodestructive process that impacts clinical outcomes and often necessitates surgical intervention. The potential for a developmental continuum between the two conditions remains an open question requiring further investigation.