138 With uncemented ﬁxation, primary stability is most important, as it facilitates osseointegration and thereby secondary stability. Both uncemented stems and cemented loaded taper stems are meant to be somewhat ‘‘loose’’ shortly after surgery. A relatively high amount of migration is conse- quently expected when the patients start weight-bearing. In contrast, the composite construction should be mechani- cally stable after setting the cement. Only a small amount of migration is then to be expected during early postoper- ative rehabilitation. When levels of early migration are expected to vary due to differences in ﬁxation, implant design, etc., it could be wise to disregard early migration data so as to make study comparisons more comprehensive. Early postoperative RSA measurements typically serve as a baseline for mea- sures of implant movement. To overcome expected dif- ferences in early implant movements, 2 or 3 years of data have been suggested for use as the baseline when com- paring levels of migration [10]. The rationale of predicting medium- to long-term prosthetic loosening based on short-term migration data is based on publications that focus on different implants and different measurement techniques [6, 7, 11, 12]. Implant-speciﬁc migration data could be useful to improve the prediction of late implant loosening based on short-term migration data. Background data from well- functional, nonrevised total hip replacements are then needed to establish acceptable limits of femoral stem migration. In the present RSA study, we describe the migration pattern of the Charnley hip stem in a group of well-functioning patients at 5-year follow-up. Materials and methods The study was approved by the Norwegian Technical and Scientiﬁc University Central Region Ethics Committee (reference 094-02), and conducted in accordance with the Declaration of Helsinki. Originally, this study was designed as a 2-year prospective randomized cohort RSA study to investigate the stability of the Charnley ﬂange 40 femoral stem prosthesis ﬁxated with either Palacos R or SmartSet HV cement. No signiﬁcant dif- ference in stem ﬁxation was found at the 2-year follow-up [13]. According to the clinical evaluation, all patients were performing very well clinically and the study was extended to include a 5-year follow-up. The extension was approved by the Ethics Committee. The main purpose of the study was then to describe the migration pattern of the Charnley stem, regardless of the type of cement employed. The patients were recruited from Trondheim University Hospital and operated on by one experienced surgeon 123 J Orthopaed Traumatol (2012) 13:137–143 (OSH). Thirty-ﬁve patients, representing 36 hips, were asked, and all agreed to participate. Informed patient consent was signed on the day of surgery. Patients with an existing condition, such as malignancy, pregnancy, severe osteoporosis, corticosteroid treatment, disabling musculoskeletal problems (other than in the hips), as well as patients who had already participated in a clinical study with an investigational product within the last 6 months were not invited to participate. No exclusions were made based on these conditions. The 23 patients were operated between October 2002 and October 2003. A bilateral procedure where both hips received the Palacos cement was performed in one patient. Mean (range) age and mean (range) weight at surgery were 69 (60–76) years and 75 (60–98) kg, respectively. At ﬁve- year follow-up 22 patients were diagnosed with osteoar- thritis and one patient with congenital hip dysplasia. The cement randomization was performed preopera- tively by a computer program (SAS version 8). An equal number of hips was allocated to each cement group. No stratiﬁcation based on age or gender was made. The cement type to be used was revealed peroperatively. Differences in color and handling made the surgeon aware of the cement type allocated, while the patients were kept unaware. The Charnley ﬂanged 40 prosthesis (DePuy Interna- tional, Leeds, UK) was implanted. This is a noncollared, shape-closed, stem with a proximal ﬂange. The Charnley prosthesis was manufactured with tantalum beads mounted on stainless towers. One tower was ﬁxed to the distal tip of the stem and one to the proximal shoulder. The central point of the prosthetic head served as the third marker (Fig. 1). All patients received the standard Charnley Ogee cup (DePuy International, Leeds, UK) with no embedded tantalum beads. A third-generation cementing technique incorporating retrograde ﬁlling and distal occlusion (Cement Restrictor, DePuy International) during pressuri- zation was used for all patients. Palacos R was stored at 8 C for a minimum of 24 h before use, while Smar- tSet HV was stored at 21 C. All cements were mixed using a vacuum (Cemvac system, DePuy CMW, Black- pool, UK). For each patient, both the femoral and the acetabular components were ﬁxated with the same type of cement. A posterolateral surgical approach was used, with a lateral incision. The femoral canal was opened through the piriformis fossa and prepared with a 12 mm central reamer, followed by a 1 mm all-direction oversized broach. Intrafemoral pulsed lavage followed by a temporary 1 % adrenalin-soaked sponge were applied to prepare the cavity prior to cementing. We performed the RSA follow-up according to the Selvik method [14]. Nine tantalum beads (0.8 mm in diameter) were implanted to serve as references: ideally