The role of fretting damage in total hip arthroplasty with modular design hip joints -evaluation of retrieval studies and experimental simulation methods.

Retrieval studies of total hip arthroplasty were reviewed to assess the clinical relevance of fretting damage on the clinical outcome of total hip arthroplasty with modular design artificial hip joints. In this case, fretting denotes the small rel-ative displacement between the two contacting surfaces at the taper joint of a modular hip prosthesis under cyclic loading caused by walking. Fretting causes a local disruption of the passivation surface layer exposing new metal to the aggressive body envi-ronment. The most important consequence is the release of metal ions and small particles. In spite of evidence that fretting plays a role in the corrosion of taper joints in modular hip implants, the statistics of the retrieval studies is too poor for a quantita-tive assessment. Moreover, the complexity of interacting mechanical loading, surface damage and corrosion leads to apprecia-ble difficulties in the experimental description of the phenomenon and the terminology used. A rather exhaustive list of experi-mental methods for in vitro fretting testing is presented. The difficulties related with accelerated testing using excessive dis-placement amplitudes or high frequencies are discussed. The necessity for alternative methods that allow in situ monitoring of metal ion and particle release with sufficient sensitivity under meaningful experimental conditions has been underlined. As an alternative to electrochemical methods, the possibility to measure subnanogram material release by using radiotracer techniques is demonstrated. (Journal of Applied Biomaterials & Biomechanics 2004; 2: 121-35).