146. A LARGE DIAMETER HEAD METAL-METAL THA RELEASES A SIGNIFICANTLY GREATER AMOUNT OF METAL ION COMPARED TO HIP RESURFACING

Abstract

Purpose: The long term exposure to metal ions released from metal-metal articulations is worrying. Studies have shown comparable ion level between metal-metal HR and 28mmTHA. No study has analyzed the amount of ion released from LDH-THA. We compared the amount of ion released from HR and LDH-THA from the same manufacturer.

Method: Whole-blood concentrations of Cobalt was measured prospectively (pre op, 3, 6, 12, 24 months) with HR-ICPMS in 74 HR and 54 LDH-THA with the same metal bearing characteristics and acetabular component (monoblock Cobalt-Chrome with titanium plasma-spray coating). The femoral head of LDH-THA was inserted on a titanium stem with a Cobalt-Chrome adapter sleeve to adjust offset and leg length.

Results: Demographic data was similar. The pre op Cobalt level (ug/L) were 0.10 vs. 0.11, 3 months 0.90 vs. 0.84, 6 months 0.90 vs. 1.28, 12 months 0.68 vs.1.75, and 24 months 0.56 (5.6X preop level) vs. 1.82 (16.5X preop level) in the HR and LDH-THA groups, respectively. The cobalt level decreased after 6 months in HR, whereas it was still increasing at 2y with LDH-THA.

Conclusion: In order to reduce wear and ion release from metal-metal bearing, most manufacturers focus research on improvements at the bearing surfaces. This study has shown that the simple addition of a sleeve with 2 modular junctions can results in a dramatic increase in ion release, diminishing the value of improvements made at the bearing surface. The total amount of ion released from a metal-metal implant should be considered globally and as such, better modular taper designs should be developed.