Introduction: The C-stem (DePuy, Leeds, UK) is triple tapered, polished and collarless. These features can facilitate distal stem migration within the cement mantle, a phenomenon first noticed on radiographs and later confirmed by radiostrereometric analysis (RSA) for the double tapered polished Exeter stem (Stryker, Mahwah, NJ). Low revision rates are reported for the Exeter stem and the view that early migration predicts later failure has not been confirmed with double tapered designs. If a triple tapered stem has any advantages is however not known

Patients and methods: 33 primary hip arthroplasties with a median age of 66 (46–74) years were followed for 2 years with radiostereometric analysis (RSA) at 3 months, 6 months, 1, 2 and 3 years. The diagnosis was primary osteoarthrosis in all hips. Both migration and rotation were studied.

Results: All the stems migrated distally and posteriorly within the cement mantle. The median distal migration was 1.47 mm at 3 years and the median posterior migration was 1.56 mm at 3 years. All the stems rotated towards retroversion and median rotation at 3 years was 2.0°. For all the other directions the prosthesis was stable up to 3 years

Discussion: The C-stem migrates and rotates more than cemented prostheses of other designs. Compared with other tapered prostheses the distal migration is at the same level but posterior rotation is higher and furthermore it migrates posteriorly, which the other tapered stems do not. If this migration/rotation pattern is tolerable without risk of prosthetic failure needs to be studied further, but at present there is no indication from the available clinical results for the C-Stem that this pattern is deleterious.

We used roentgen stereophotogrammetric analysis to follow 33 C-stem femoral components for two years after primary total hip arthroplasty. All components migrated distally and posteriorly within the cement mantle. The mean distal migration was 1.35 mm (sd 0.62) at two years and the mean posterior migration was 1.35 mm (sd 0.69) at two years. All the femoral components rotated into retroversion with a mean rotation at two years of 1.9° (sd 1.1). For all other directions, the prosthesis was stable up to two years. Compared with other tapered prostheses, the distal migration of the C-stem is the same, but posterior rotation and posterior migration are greater.