Incidence and clinical relevance of cage subsidence in anterior cervical discectomy and fusion: a systematic review

Background The placement of intervertebral cages in anterior cervical discectomy (ACDF) supposedly maintains foraminal height. The most commonly reported cage-related complication is subsidence, although it is unknown whether a correlation between subsidence and clinical outcome exists. Aim To assess the incidence and relevance of subsidence. Methods Literature searches were performed in PubMed, MEDLINE, Embase, Web of Science, COCHRANE, and CENTRAL. The inclusion criteria were as follows: ≥ 20 patients, ADCF with cage, subsidence assessed, and primary data. Risk of bias was assessed using adjusted Cochrane checklists. Results Seventy-one studies, comprising 4784 patients, were included. Subsidence was generally defined as ≥ 3-mm loss of height comparing postoperative intervertebral heights with heights at last follow-up. Mean incidence of subsidence was 21% (range 0–83%). Of all patients, 46% of patients received polyether-ether-ketone (PEEK) cages, 31% received titanium cages, 18% received cage-screw-combinations, and 5% received polymethyl-methacrylate (PMMA) cages. Patients treated with cage-screw-combinations had significantly less subsidence than patients treated with PEEK, titanium, or PMMA cages (15.1% vs. 23.5% vs. 24.9% vs. 30.2%; p