J Orthopaed Traumatol (2012) 13:137–143 DOI 10.1007/s10195-012-0187-x O R I G I N A L A R T I C L E The migration pattern of the Charnley femoral stem: a ﬁve-year follow-up RSA study in a well-functioning patient group Kristin Haugan • Otto S. Husby • Jomar Klaksvik • Olav A. Foss Received: 1 July 2011 / Accepted: 10 March 2012 / Published online: 11 May 2012 The Author(s) 2012. This article is published with open access at Springerlink.com Abstract Background Implant stability is considered vital to long- time implant survival in total hip arthroplasty (THA), since loose implants are reported to be a major cause of hip revision. There is an association between early implant micromotion and increased risk of revision. More implant- speciﬁc data are needed to establish acceptable levels of early implant movement. Materials and methods Thirty-ﬁve patients (36 hips) undergoing Charnley THA were followed with repeated clinical, radiographic, and radiostereometric analysis (RSA) over 5 years. Twenty-three patients attended 5 years postoperatively. Results The patient group was well functioning based on the radiological and clinical evaluations. The stems con- stantly moved up to 5 years postoperatively, with subsi- dence, retroversion, and varus tilt, based on the RSA. Conclusion Continuous movement of the Charnley stem was observed up to 5 years postoperatively in a well- functioning patient group. The migration data presented herein could be useful when deﬁning acceptable migration limits for certain types of cemented femoral stems. Keywords RSA Migration pattern Charnley THR Five-year follow-up K. Haugan (&) O. S. Husby J. Klaksvik O. A. Foss Orthopaedic Research Centre, Trondheim University Hospital, 7006 Trondheim, Norway e-mail: kristin.haugan@ntnu.no O. S. Husby Orthopaedic Department, Trondheim University Hospital, 7006 Trondheim, Norway Introduction Implant stability inﬂuences the revision rate observed in total hip arthroplasty (THA). According to the Swedish, Australian and Norwegian hip registers, aseptic loosening is the most common cause of revision [1–3]. Revision surgery is expensive to both patients and the community. Major efforts have been made to reduce these numbers from the earliest days of THA. Radiostereometric analysis (RSA) has become a gold standard when measuring implant migrations with respect to the cement mantle as well as the surrounding bone [4]. RSA can describe early implant migration, and is therefore well suited and recommended when introducing new implants into clinical use and minimizing the number of enrolled patients [5]. The main rationale for monitoring early implant migration is based on results from clinical studies reporting an association between early subsidence and increased risk of early or mid-term hip implant revision. Early migration [6], continuous migration [7], and subsidence in combination with medial and posterior migration [6] are of concern. However, when deﬁning acceptable limits for migration, factors such as measurement procedures, implant design, and ﬁxation principles should be taken into account. The level of early implant stability is mainly determined by the ﬁxation method used. In cement ﬁxation of femoral stems, two different principles apply [8, 9]. In a composite construction, such as the Charnley stem, there should be perfect bonding between stem and cement. In contrast, there is the construction in which the stem is not intended to be bonded to the cement, but rather to act as a ‘‘loaded taper’’ that is constrained by its surrounding cement man- tle, such as the Exeter stem. 123