Study characteristics of included randomized controlled trials (RCTs).

Gathered information refer to patients with at least one metallic part of the bearing being investigated on metal ions.
Studies were summarized due to multiple reporting of identical patient population.
RCT: randomised controlled trial; comparison of 2 interventions, being different regarding e.g. bearing or type of implant; incl. metal ion measurement for all groups.1: Number of patients (with at least one metallic part of the bearing) being investigated on metal ions/total number of patients being investigated.
on metal ions.
2: Rounded mean age of patients with at least one metallic part of the bearing/rounded mean age of total number of patients being investigated.
on metal ions.
*: Rounded weighted mean.
3: BMI  =  Body Mass Index.
4: THA  =  Total hip replacement.
5: HRA  =  Hip resurfacing arthroplasty.
MoM: Metal-on-Metal bearing.
MoP: Metal-on-Polyethylene bearing.
MoC: Metall-on-Ceramic bearing.
CoC: Ceramic-on-Ceramic bearing.
CoP: Ceramic-on-Polyethylene bearing.
6: Femoral head size 28–32 mm; small head.
7: Femoral head size ≥36 mm; large head.
**incl. Protek, AlloPro, Sulzer Orthop., Centerpulse, Zimmer.
***incl. Landander.
UCLA: Activity Score, University of California, Los Angeles.