Polyethylene Dual Mobility Liners Show Minimal Polyethylene Changes in Early Retrievals

Area of Science:

• Orthopedic Surgery
• Biomaterials Science
• Medical Device Engineering

Background:

• Dual mobility (DM) liners aim to reduce instability in total hip arthroplasty.
• Motion in DM liners occurs primarily at the femoral head and acetabular liner's inner bearing.
• The impact of this motion on polyethylene material characteristics remains largely unknown.

Purpose of the Study:

• To assess cross-link (XL) density and oxidation index (OI) in the inner and outer bearing articulations of DM liners.
• To investigate if the motion within DM liners alters polyethylene material properties.

Main Methods:

• Thirty-seven DM liners implanted for over 2 years were analyzed.
• Polyethylene segments from inner and outer bearings were tested for XL density using swell ratio.
• Oxidation index (OI) was measured using Fourier transform infrared spectroscopy on microtome slices.

Main Results:

• Median XL densities were similar between the inner and outer bearings (0.17 mol/dm³).
• The inner bearing exhibited a significantly higher OI (0.16) compared to the outer bearing (0.13).
• OI was inversely correlated with XL density (r = -0.50, P = .002).

Conclusions:

• Minor differences in oxidation were observed between the inner and outer bearings of DM constructs.
• Low oxidation levels, even after an average of 3 years, are unlikely to compromise the mechanical integrity of the polyethylene material.