Fretting Corrosion Test Method Development and Application to Orthopaedic Implant Design

Recent advances in modularity of total hip replacement offer the surgeon greater intraoperative flexibility to accurately reconstruct the hip joint. Numerous design and clinical factors are associated with the fretting and corrosion performance of implant modularity. To predict the clinical performance of modular implant designs in a timely manner, it is necessary to accelerate testing using load and environmental parameters. Retrieval examination and testing of two femoral hip modular head/stem taper designs was conducted to refine the test parameters to match the clinical observations. Specifically, load, number of cycles, temperature and acidity (pH) of the environment were varied. Using qualitative examination, the final combination of test parameters that produced taper wear that most resembled the retrieved taper surfaces was selected. A methodology for quantitative assessment was then developed to provide a measure of differentiation between designs.

We aimed to compare the wear debris generation of a clinical proven CoCr femoral head on Tivanium (Ti-6Al-4V) fixed (non-modular) neck implant to the wear debris generation of modular neck femoral implants using a Tivanium neck or CoCr neck in combination with a Tivanium stem. In agreement with previous retrieval studies, testing of head/neck tapers demonstrated that femoral head offset plays a significant role in the fretting corrosion performance. Interestingly, at the longest femoral neck offset, the Tivanium modular neck implant (M/L Taper with Kinectiv Technology) demonstrated less total wear debris generation than that demonstrated by the fixed neck implant. The CoCr modular neck combination demonstrated significantly more wear debris than the Tivanium neck construct. Material selection is critical to the fretting corrosion performance of modular neck implant designs. Titanium alloy was found to be superior to CoCr alloys when paired with Ti-6Al-4V femoral stems. This result is consistent with the increased observation of fretting corrosion of mixed-alloy head/neck taper systems previously reported.