Aims: The aim of this study is to report the pre-clinical validation and clinical experience with modular neck primary prosthesis.

Introduction: Modular acetabular designs are widespread used in primary THA for their versatility while little experience is reported with modular femoral designs. Stem modularity could be useful when the anatomy is overthrown and for mini-incision approaches, providing an increased adaptability without any need for a large inventory or expensive custom made prostheses.

Methods: The fretting-corrosion behavior of the neck-stem coupling and the amount of particulate released under simulated physiological activities were investigated. In vitro tests were performed in Ringer’s solution loading the stem up to 20 millions cycles (i.e. 20 yrs) according to ISO 7206. From January 1995 to December 2001, 864 primary surgeries were performed with a modular stem. There were 458 women and 406 men; the mean age was 55 years (16–81 years). The main pre-operative diagnosis was primary arthritis (58.1%), the second CHD (22.2%). The stem survival was estimated by the Kaplan-Meier method.

Results: Evidence of primary corrosion was not found, conversely areas showing fretting damage were seen. The amount of fretted material was estimated in less than 1mg/year. Clinically 3 stems were revised, 2 for recurrent dislocation, 1 for stem subsidence, none for mechanical failure. At 6 years the estimated stem survival is 99.4%.

Conclusions: Modular stems have shown excellent clinical and mechanical behavior. The amount of fretting debris product is negligible taking that a stable prosthesis is likely to produce more than 10mg/year of metal debris.