Reduced Wear of Cross-linked UHMWPE Using Magnesia-stabilized Zirconia Femoral Heads in a Hip Simulator

Background To reduce wear, the ideal bearing surface in joint arthroplasty should be smooth and hydrophilic. Ceramics generally offer better wettability than metals and can be polished to a smoother finish. However, clinical studies have found no reduction in liner wear when using yttria-stabilized zirconia (Y-TZP) instead of cobalt chromium alloy (CoCr) femoral heads.

Question/purposes We (1) determined whether a hard, diamond-like carbon (DLC) coating would enhance the wettability of CoCr and magnesia-stabilized zirconia (Mg-PSZ) femoral heads without increasing roughness, and (2) compared their wear performance.

Methods In an observational study limited to CoCr and Mg-PSZ heads, we measured roughness and contact angle on as-received and DLC-coated heads. Eight heads then were subjected to 11 million cycles of wear in a hip simulator against cross-linked ultrahigh molecular weight polyethylene (XLPE) liners.

Results Mg-PSZ femoral heads were smoother and more hydrophilic than CoCr heads. Although DLC coatings did not reduce roughness, they reduced the contact angle of CoCr and Mg-PSZ substrates, which may provide enhanced lubrication in vivo. In hip simulator tests, liners bearing against CoCr heads wore at a greater rate compared with Mg-PSZ heads. The DLC coating on Mg-PSZ heads did not reduce wear further.

Conclusions The wear rate of XLPE versus Mg-PSZ was seven times less than CoCr heads, probably owing to lower roughness and greater wettability of Mg-PSZ heads.

Clinical relevance The use of Mg-PSZ femoral heads should lead to reduced wear in vivo compared with CoCr heads, but the clinical benefit of DLC-coated Mg-PSZ is unclear.