161. Metal-on-metal vs metal-on-plastic artificial discs in 2-level anterior cervical disc replacement: a meta-analysis with follow up of 5 years or more

Abstract

<h3>BACKGROUND CONTEXT</h3> Anterior cervical discectomy and fusion (ACDF) is a well-established procedure that has long been considered the standard treatment for degenerative disc disease (DDD). Despite positive clinical outcomes, accelerated rates of adjacent segment disease (ASD) in ACDF, especially in two-level surgery, has led spinal surgeons to increasingly use anterior cervical disc replacement (ACDR) as an alternative. However, long-term success may be limited by the properties inherent to the devices utilized. The use of metal-on-metal (MM) bearings in total joint replacement, for example, has been hypothesized to significantly decrease volumetric wear rates, but subsequent complications associated with metallosis have prompted joint surgeons toward using metal-on-plastic (MP) or ceramic implants more commonly. Furthermore, MP implants in total hip arthroplasty have been associated with superior clinical outcomes and durability when compared to MM implants. Although highlighted in joint arthroplasty studies, long-term outcomes between differing biomaterial composites in ACDR have not been thoroughly investigated. <h3>PURPOSE</h3> The purpose of this study was to evaluate the rates of ASD, reoperation rates, complications and patient reported clinical outcomes of MM vs MP artificial discs in two-level ACDR for the treatment of cervical DDD. <h3>STUDY DESIGN/SETTING</h3> Meta-analysis and systematic review. <h3>PATIENT SAMPLE</h3> A total of 980 patients (442 MM, 538 MP). <h3>OUTCOME MEASURES</h3> 1) Rate of ASD, 2) reoperation rate, 3) complications, 4) patient reported clinical outcomes (NDI, VAS-neck, VAS-arm). <h3>Methods</h3> A systematic search strategy of three electronic databases (PubMed, CINAHL Plus and SCOPUS) was conducted utilizing terms related to 2-level ACDR. All studies included were published in the past 5 years, had a sample size of >10 patients, and reported data on adjacent segment disease. Cadaver studies, non-English manuscripts and studies in which only single-level ACDR was investigated were excluded. A total of 7 studies were included in this analysis. Studies were analyzed for demographic data, clinical outcome scores (NDI, VAS-neck and VAS-arm), rates of ASD, complications and reoperation proportions. A random-effects model of meta-analysis was used for groups that were determined to be heterogenous and a fixed-effects model was utilized for groups that were not. An overlap of 95% confidence intervals suggests no statistically significant difference at the p<0.05 level. <h3>Results</h3> Seven studies were included with data on 980 patients (442 MM, 538 MP). 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 NDI was 34.42 (95% CI, 32.49-36.36) and 29.72 (95% CI, 27.15-32.29) for the MM and MP groups, respectively. The mean improvement in VAS-neck was 11.20 (95% CI, 10.69-11.70) and 8.78 (95% CI, 7.81-9.74) for the MM and MP groups, respectively. The mean improvement in VAS-arm was 10.73 (95% CI, 9.83-11.63) and 8.49 (95% CI, 7.59-9.39) for the MM and MP groups, respectively. Reoperation was needed in 1.36% (95% CI, 0.61-2.99) of patients who underwent ACDR with an MM implant compared to 5.33% (95% CI, 3.68-7.65) of patients with an MP implant. The MM cohort had a larger proportion of patients with ASD who underwent subsequent surgery at an adjacent level (7.89% MM vs 1.91% MP). Heterotopic ossification and dysphagia were the most common complications in both groups, and the incidence of each was significantly higher in the MP cohort. <h3>Conclusions</h3> Our present meta-analysis suggests that the use of MM artificial discs in 2-level ACDR results in superior clinical outcome scores with a lower complication profile and reoperation rate, but higher rates of ASD compared to MP discs after a follow-up period of 5 years or more. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.