Does bearing size influence metal ion levels in large-head metal-on-metal total hip arthroplasty? A comparison of three total hip systems.
BACKGROUND
The purpose of the study was twofold: first, to determine whether there is a statistically significant difference in the metal ion levels among three different large-head metal-on-metal (MOM) total hip systems. The second objective was to assess whether position of the implanted prostheses, patient demographics or factors such as activity levels influence overall blood metal ion levels and whether there is a difference in the functional outcomes between the systems.


METHODS
In a cross-sectional cohort study, three different metal-on-metal total hip systems were assessed: two monoblock heads, the Durom socket (Zimmer, Warsaw, IN, USA) and the Birmingham socket (Smith and Nephew, Memphis, TN, USA), and one modular metal-on-metal total hip system (Pinnacle, Depuy Orthopedics, Warsaw, IN, USA). Fifty-four patients were recruited, with a mean age of 59.7 years and a mean follow-up time of 41 months (12 to 60). Patients were evaluated clinically, radiologically and biochemically. Statistical analysis was performed on all collected data to assess any differences between the three groups in terms of overall blood metal ion levels and also to identify whether there was any other factor within the group demographics and outcomes that could influence the mean levels of Co and Cr.


RESULTS
Although the functional outcome scores were similar in all three groups, the blood metal ion levels in the larger monoblock large heads (Durom, Birmingham sockets) were significantly raised compared with those of the Pinnacle group. In addition, the metal ion levels were not found to have a statistically significant relationship to the anteversion or abduction angles as measured on the radiographs.


CONCLUSIONS
When considering a MOM THR, the use of a monoblock large-head system leads to higher elevations in whole blood metal ions and offers no advantage over a smaller head modular system.
James
J
Smith
David
D
Lee
Kamal
K
Bali
Pam
P
Railton
David
D
Kinniburgh
Peter
P
Faris
Deborah
D
Marshall
Brian
B
Burkart
Orthopaedic Trauma and Lower Extremity Reconstruction, University of Calgary, #0444 3134 Hospital Drive NW Calgary AB T2N 5A1, Canada. jnpowellemail@yahoo.ca.
James
J
Powell
D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation* / Q000592:standards*; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006622:Hip Prosthesis / Q000592:standards*; D006801:Humans; D017136:Ion Transport / Q000502:physiology; D008297:Male; D008670:Metals / Q000097:blood*; D008875:Middle Aged
D008670:Metals