James A. Rand Young Investigator's Award: Questioning the “Nickel Free” Total Knee Arthroplasty

Background: A study was performed to measure metal ions present in the knee joint after performing a total knee arthroplasty (TKA) with standard cobalt chromium (CoCr) components as well as with “nickel-free” oxidized zirconium femoral and titanium tibial (OxZr/Ti) components. Methods: Knee joint fluid was collected prior to arthrotomy, and on postoperative day one to determine the amount of metal debris generated when performing a TKA with standard instrumentation from consecutive cases with CoCr components (n = 24) and OxZr/Ti components (n = 16). Results: CoCr implant patients had statistically higher levels of nickel (Ni) (29.7%, P =.033), cobalt (Co), (1,100.7%, P <.0001) and chromium (Cr) (118.9%, P <.0001) postoperatively. The cutting blocks and sawblades do not contain Co, which therefore must have come from the components. The metal ions generated from the sawblades and cutting blocks, therefore, could be discerned from the OxZr/Ti whose components don't contain Co, Cr, or Ni. The OxZr patients had significantly higher Cr (9.5×, P <.001) and Ni (5.1×, P <.001) post-TKA vs pre-TKA; Co levels were not significantly different as expected with the absence of Co in the components (P =.60). The Ni levels generated in performing an Oxinium TKA was 3.3 times higher than when performing a CoCr TKA (1.37 vs. 41 ppb, P <.001). Conclusions: The substantial degree of Ni generation resulting from performing a hypoallergenic “nickel-free” TKA calls into questions the rationale of utilizing more expensive lower Ni components on the basis of known or suspected Ni or Cr allergy.