Bilateral total hip replacement: periprosthetic pseudotumor collections are more prevalent in metal-on-metal implants compared to non-metal-on-metal ones

Background Metal-on-metal (MoM) hip prostheses were shown to have high failure rates including the formation of periprosthetic cystic masses called periprosthetic pseudotumor collections (PPCs). Purpose To compare MRI prevalence and size of PPCs in patients after bilateral total-hip-replacement (THR) in which at least one hip was replaced by a MoM prosthesis. Material and Methods All sequential MRI examinations of patients with bilateral THR in which at least one is MoM (2010-2013) were retrospectively evaluated. MRIs were analyzed separately by two readers for the presence and size of PPCs. These were compared between MoM and non-MoM implants and between patients with unilateral or bilateral-MoM prostheses. Blood metal ion levels were also compared. Results Seventy hips of 35 patients (male:female ratio, 9:26; mean age, 64 years; age range, 35-82 years) were assessed. Sixteen patients (45%) underwent bilateral MoM-THRs and 19 (55%) had one MoM and the other non-MoM, yielding 51 MoM THRs and 19 non-MoM THRs. Twenty-eight PPCs were detected in 19 patients (54%): 26 in MoM THRs (51%) and two in non-MoM THRs (10.5%, P=0.00009). The mean PPC volume in the MoM implants (107 mm(3)) was higher than that of the non-MoM implants (18 mm(3), P=0.49). Cobalt/chromium blood levels were 78 mu g/L/25 mu g/L for bilateral MoM THRs and 21 mu g/L/10 mu g/L for unilateral MoM implants (P=0.1 and 0.16, respectively). Conclusion PPCs are more prevalent in MoM THRs compared to non-MoM THRs. Larger PPC volumes and higher blood metal ion levels were detected in patients with bilateral MoM THRs compared to unilateral MoM THRs (P>0.05).