Comparison between component designs with different femoral head size in metal-on-metal total hip arthroplasty; multicenter randomized prospective study.

We prospectively studied 78 prostheses with conventional femoral head and 86 prostheses with large head (Magnum) of metal-on-metal total hip arthroplasty (MoM THA) with two years follow-up.Clinical outcomes and blood metal ion were evaluated.There were no significant differences of clinical outcomes between groups. 1.17 ± 1.01 μg/L of blood cobalt ion in Magnum was significantly lower than 1.99 ± 2.34 μg/L in conventional group. No dislocation was observed in Magnum while one dislocation in conventional group. MoM THA with large head is useful if the implants are positioned in appropriate alignment, however longer follow-up will be necessary. Clinical Trial Registration: NCT01010763 (registered on ClinicalTrials.gov).