The use of metal-on-metal (MoM) artificial discs in two-level anterior cervical disc replacement (ACDR) results in superior patient-reported clinical outcome scores compared to metal-on-plastic (MoP) artificial discs, a meta-analysis recently published in The Spine Journal by Daniel Coban (St Joseph’s University Medical Center, Paterson, USA) et al has found.
However, the meta-analysis also indicates higher rates of adjacent segment disease (ASD) requiring secondary surgery when using MoM compared with MoP discs after a follow-up period of five years or more. In addition, the incidence of heterotopic ossification (HO) was found to be significantly higher in the MoM cohort, but the incidence of dysphagia was found to be significantly lower.
Seven studies were included in the meta-analysis with data on 980 patients (442 MoM, 538 MoP). All studies included had a sample size of more than 10 patients, had a minimum five-year follow-up, and reported data on adjacent segment disease. The study population was 52.84% female, with a mean age of 48.01 years, and a mean follow-up of 85.66 months.
The mean improvement in Neck Disability Index (NDI) was 34.42 (95% confidence interval [CI], 32.49–36.36) and 29.72 (95% CI, 27.15–32.29) for the MoM and MoP groups, respectively.
The mean improvement in Visual Analogue Score (VAS)-neck was 11.2 (95% CI, 10.69–11.7) and 8.78 (95% CI, 7.81–9.74) for the MoM and MoP groups respectively, and mean improvement in VAS-arm was 10.73 (95% CI, 9.83–11.63) and 8.49 (95% CI, 7.59–9.39).
A total of 3.85% (95% CI, 2.4–6.1) of patients who underwent ACDR with a MoM implant required reoperation compared to 5.33% (95% CI, 3.68–7.65) of patients with a MoP implant.
HO and dysphagia were the most common complications in both groups. The MoM cohort showed a higher incidence of HO (72.62% vs. 21.07%), but a lower incidence of dysphagia (0.96% vs. 16.31%) compared to the MoP cohort.
The MoM cohort had a larger proportion of patients with ASD who underwent subsequent surgery at an adjacent level (7.89% MoM vs. 1.91% MoP).