To unlock this feature and to subscribe to our weekly evidence emails, please create a FREE orthoEvidence account.


Already Have an Account?

Visit our Evidence-Based Covid-19 Website and Stay Up to Date with the latest Research.
Ace Report Cover

Increased mortality with metal-on-metal total hip arthroplasty over long-term follow-up

Cite This
+ Favorites
Cite This
+ Favorites
Author Verified

Increased mortality with metal-on-metal total hip arthroplasty over long-term follow-up

Vol: 6| Issue: 1| Number:27| ISSN#: 2564-2537
Study Type:Therapy
OE Level Evidence:2
Journal Level of Evidence:N/A

Increased Mortality in Metal-on-Metal versus Non-Metal-on-Metal Primary Total Hip Arthroplasty at 10 Years and Longer Follow-Up: A Systematic Review and Meta-Analysis.

PLoS One. 2016 Jun 13;11(6):e0156051. doi: 10.1371/journal.pone.0156051. eCollection 2016

Did you know you're eligible to earn 0.5 CME credits for reading this report? Click Here


38 randomized controlled trials and 9 observational studies were included in this systematic review and meta-analysis to compare mortality and morbidity rates between metal-on-metal total hip arthroplasty (MOM THA) and non-metal-on-metal THA (non-MOM THA). Results of the meta-analysis indicate no significant differences in mortality rate within 5 years, or from 5-10 years. However, mortality rate was significantly higher among MOM THA groups compared to non-MOM THA groups in studies with >10-year follow-up. Additionally, a trend towards a greater rate of surgical revision was observed in the MOM THA group.

Publication Funding Details +
None disclosed

Risk of Bias


Reporting Criteria


Fragility Index


Were the search methods used to find evidence (original research) on the primary question or questions stated?

Was the search for evidence reasonably comprehensive?

Were the criteria used for deciding which studies to include in the overview reported?

Was the bias in the selection of studies avoided?

Were the criteria used for assessing the validity of the included studies reported?

Was the validity of all of the studies referred to in the text assessed with use of appropriate criteria (either in selecting the studies for inclusion or in analyzing the studies that were cited)?

Were the methods used to combine the findings of the relevant studies (to reach a conclusion) reported?

Were the findings of the relevant studies combined appropriately relative to the primary question that the overview addresses?

Were the conclusions made by the author or authors supported by the data and or analysis reported in the overview?

How would you rate the scientific quality of this evidence?

Yes = 1

Uncertain = 0.5

Not Relevant = 0

No = 0

The Reporting Criteria Assessment evaluates the transparency with which authors report the methodological and trial characteristics of the trial within the publication. The assessment is divided into five categories which are presented below.




Accessing Data


Analysing Data





Detsky AS, Naylor CD, O'Rourke K, McGeer AJ, L'Abbé KA. J Clin Epidemiol. 1992;45:255-65

The Fragility Index is a tool that aids in the interpretation of significant findings, providing a measure of strength for a result. The Fragility Index represents the number of consecutive events that need to be added to a dichotomous outcome to make the finding no longer significant. A small number represents a weaker finding and a large number represents a stronger finding.

Why was this study needed now?

Recent observational studies providing long-term follow-up have demonstrated an increased risk of mortality with the first generation of metal-on-metal total hip arthroplasty implants. However, conflicting data has been presented for second-generation metal-on-metal implants. Metal-on-metal total hip arthroplasty implants are still in use today in some settings and a comprehensive meta-analysis is needed to determine the mortality and morbidity of the different generations of MOM THA implants over the long-term.

What was the principal research question?

What are the overall mortality and morbidity rates of first- and second-generation metal-on-metal bearings when compared to non-metal-on-metal bearings in primary total hip arthroplasties evaluated in randomized controlled trials and observational studies?

Study Characteristics -
Data Source:
Electronic databases PubMed, MEDLINE, EMBASE, Web of Science, Cochrane, CINAHL, and Academic Premier were searched from their inception to the end of March 2015. Additionally, journal publishers ScienceDirect & Wiley and clinical trial registries;, WHO International Clinical Trials Registry Platform, Multi-register, and the DutchTrial Registry were searched.
Index Terms:
Searches were tailored to each individual search engine. Search terms that related to; 1) implant types (metal-on-metal, resurfacing, and brand names), 2) total hip arthroplasty, and 3)randomized controlled trials were used.
Study Selection:
Study selection was performed independently by two reviewers and disagreements were resolved by consensus or a separate reviewer. inclusion criteria for RCTs included; 1) primary total hip arthroplasty, 2) comparison of metal-on-metal bearing with non-metal-on-metal bearings, 3) randomized controlled trial or quasi-randomized controlled trial, 4) follow-up for at least 3 months. Studies were excluded if they only included bilateral cases that compared these two types of prostheses or did not report mortality/morbidity. Inclusion for observation studies included; 1) primary total hip arthroplasty, 2) comparison of metal-on-metal bearing with non-metal-on-metal bearings, 3) mortality reported, 4) follow-up for at least 3 months. A total of 38 randomized controlled trials (3,957 patients; MOM THA: 1,806, Non-MOM THA: 2,151) and 9 observational studies were selected for final inclusion.
Data Extraction:
Data extraction was performed by two independent reviewers. Data extracted included mortality and morbidity, patient demographics, study characteristics, implant specifications, and risk of bias. Disagreements were resolved by consensus or by an independent reviewer.
Data Synthesis:
An overall risk difference was calculated by pooling individual risk differences using a random effects model. All analyses were performed using the metafor package R statistics. Heterogeneity was assessed by visual inspection of forest plots and tau-squared and I-squared statistics. Randomized controlled trials of first and second generation MOM THA and observational trials of first generation MOM THA were eligible for meta-analysis. Observation trials of second generation MOM THA were considered subject to strong bias and were not eligible for meta-analysis.

What were the important findings?

  • Mortality risk difference was assessed between MOM THA and non-MOM THA at three different follow-up periods; <5 years, 5-10 years, and >10 years. No significant difference was observed within 5 year follow-up (13 RCTs; RD 0.1% [95%CI -1.3% to 1.0%]) or from 5-10 year follow-up (9; RD 0.7% [95%CI -3.0% to 1.7%]). In studies with >10-year follow-up, a significantly higher rate of mortality was observed among MOM THA groups compared to non-MOM THA groups (3 RCTs/1 Observational; RD 4.4% [95%CI1.4% to 7.4%]).
  • Observational studies of first-generation MOM THA demonstrated a trend toward increased mortality compared to non-MOM THA (RR 1.05) This finding was in line with the results from RCTs. Observational studies evaluating second generation MOM demonstrated a decreased risk of mortality for MOM THA compared to non-MOM THA, which was in contrast to long-term results from RCTs.
  • Morbidity in the form of surgical complications was reported in 26 RCTs, all evaluating second generation MOM THA in comparison to non-MOM THA. The risk of revision was greater in the MOM group RD: 0.8% [95%CI -0.1% to 1.7%] I-squared 0%, but this difference was not significant.
  • The risk of cancer was reported in 4 observational studies: 1 evaluating first generation MOM THA and 3 evaluating second generation MOM THA. The first generation MOM THA demonstrated a greater risk of cancer compared to non-MOM THA, but this increased risk was not significant, while the second generation demonstrated no difference compared to non-MOM THA.

What should I remember most?

The long-term mortality rates appear to be increased in metal-on-metal total hip arthroplasty compared to non-metal-on-metal hip arthroplasty, while mortality rate within 10 years does not appear to differ significantly. Additionally, the rate of surgical revision appears to be higher with the use of metal-on-metal total hip arthroplasty compared to non-metal-on-metal total hip arthroplasty.

How will this affect the care of my patients?

The results of this meta-analysis demonstrated a higher rate of mortality with the use of metal-on-metal implants in total hip arthroplasty in randomized controlled trials with long-term follow-up. In addition to the higher rate of mortality, there was a trend towards increased morbidity requiring surgical revision. The result from this study highlights the need for patients who have received a metal-on-metal implant in the past to be closely followed. Additionally, the result of this trial indicates that there is no case for the use of metal-on-metal THA implants due to the increased risk of mortality.

CME Image

Did you know that you’re eligible to earn 0.5 CME credits for reading this report!


Join the Conversation

Please Login or Join to leave comments.

Learn about our AI Driven
High Impact Search Feature

High Impact Icon

The OE High Impact metric uses AI to determine the impact a study will have by considering the content of the article itself. Built using the latest advances of natural language processing techniques. OE High Impact predicts an article’s future number of citations than impact factor alone.