Strengths and limitations
A limitation of this study is the relatively small cohort of 64 patients with modular femoral implants. It might not be adequate to characterize a relatively infrequent condition like trunnion corrosion. The size of our cohorts contributed to the large interquartile range seen in metal ion levels, and despite difference in some median levels between the head material groups, these failed to reach statistical difference.Furthermore, we did not have a control group of patients with native hip, without implants. Yet, the monoblock stainless steel Charnley prosthesis had similar metal ion levels as the modular Spectron EF prosthesis, regardless of femoral head material. Trunnionosis cannot account for the metal ion levels with the monoblock Charnley, showing that systemic metal ions may stem from other sources than the trunnion. The Spectron EF femoral stem was more stable than the Charnley stem in a RSA‐study when evaluated at 2 years.Our results highlight the importance of retrieval centers for understanding cause and effect relationships in THA.Another limitation with the study is that 50 patients had hip prosthesis in the other hip. Some patients also had prostheses in the knee (One strength of this study is that it was part of a randomized study, reducing the risk of selection bias. To our knowledge this is the first RCT who compares metal ion release from the femoral head materials Oxinium, CoCrMo and stainless steel. Another strong point of this study is that the taper design was identical between the CoCrMo and Oxinium modular head groups. Taper design is associated with the degree of crevice corrosion at the modular head and neck interface. Our results are therefore solely associated with head–neck material, not variance in taper design.Detecting differences in blood ion levels between groups is demanding due to small detection limits.Our study patients were quite old, so our results may not apply to younger and more active patients, who are increasingly becoming eligible for the THA procedure. The mechanical demands at the head‐trunnion in a younger population interface may be higher. Thus, any mechanically driven corrosion and rise in blood ion levels may be underestimated in the population of this study.