Anterior bone loss after cervical disc replacement: A systematic review

BACKGROUND Anterior bone loss (ABL) is a relatively easily neglected condition after cervical disc replacement (CDR). Whether this phenomenon is a radiological anomaly or a complication remains controversial. Several studies have reported the clinical characteristics of ABL and speculated on the pathogenic mechanism based on a certain type of artificial disc, while the overall understanding of ABL is lacking. AIM To describe the prevalence, impacts, and risk factors of ABL after CDR. METHODS We searched the PubMed, Cochrane Library, and Excerpta Medica databases using the terms "bone loss" or "bone remodeling" or "bone absorption" or "osteolysis" or "implant loosening" or "implant migration" or "hypersensitivity" or "hyperreactivity", "cervical disc replacement" or "cervical disc arthroplasty" or "total disc replacement". Eligible manuscripts on the prevalence and impacts of ABL were reviewed by the authors. Data extraction was performed using an established extraction form. The results of the included studies were described narratively. RESULTS Six studies met the inclusion and exclusion criteria. One was a prospective study and the others were retrospective studies. A total of 440 patients with 536 segments were included. The artificial cervical discs included Bryan, Baguera-C, Discocerv, and Mobi-C. The prevalence of ABL ranged from 3.13% to 91.89%, with a combined overall prevalence of 41.84%. ABL occurred within 6 mo and stopped 12 mo after surgery. Several cases were noted to have a self-healing process. Severe ABL resulted in segmental kyphosis, implant subsidence, and persistent neck pain. ABL may be related to heterotopic ossification. Multilevel surgery may be one of the risk factors for ABL. CONCLUSION ABL is a common condition after CDR. The underlying mechanisms of ABL may include stress concentration and injury to nutrient vessels. ABL should be considered a complication after CDR as it was associated with neck pain, implant subsidence, and heterotopic ossification.