Introduction: C-stem is a triple taper polished femoral stem. The rationale for this design is to achieve an evenly distributed proximal loading of the cement mantle. This design is thought to enhance stability of the stem inside the mantle and lead to bone remodelling medially. There is to our knowledge no randomized trial comparing this stem to a well documented stem. We chose to compare it to the best documented stem in the Norwegian arthroplasty register, the Charnley monoblock.

Methods: 70 patients scheduled for total hip replacement were randomized to either C-stem or Charnley monoblock. All received a 22 mm stainless steel head, OGGEE cup and Palacos Cement with Gentamycin. We used a transgluteal approach in all cases. Harris and Oxford hip scores were measured preoperatively and after two years. Standard X-rays were taken postoperatively and after two years. Radiostereometry (RSA) was done postoperatively and after 3,6,12 and 24 months.

Results: There was no significant difference in Harris or Oxford hip scores after two years.

RSA after two years: (table deleted)

Discussion: Polished tapered stems are designed to sink inside the mantle. Our results confirm this theory for the C-stem. The subsidence is comparable to other collarless tapered stems with good long-term survival. For all other migrations/rotations the C-stem is as stable as the Charnley monoblock. This predicts good long-term results for this stem.

Introduction: Increased wear is associated with aseptic loosening and late dislocations. Hard on hard bearings may reduce wear but still have topics of concern such as free metal ions in metal on metal bearings and the risk for fracture in ceramic articulations. Ceramic heads against conventional polyethylene is also used with the intention to reduce wear. But this effect has not been conclusively documented in the literature and is still discussed. 87 patients were operated consecutively by the same surgeon with the same surgical technique. All patients received a cemented all poly cup sterilized with irradiation in inert atmosphere and a cemented stem. Head size was 28 mm in all patients. 40 patients received cobalt-chrome heads and 47 patients aluminiumoxid heads. The patients were followed with RSA for 10 years and analysed for wear.

Results: Mean (SEM) wear for the group with cobalt chrome heads was 0.93 mm (0.13) and for the group with aluminiumoxide was 0.43 mm (0.08) (p = 0.001).

Discussion: We found significantly less wear with aluminumoxide heads compared to cobalt-chrome heads. The wear results in the cobalt-chrome group correlate well to wear values in the literature for conventional polyethylene. Although the polyethylene in this study is partly cross-linked (3Mrad) it is not clear whether these results can be extrapolated directly to the use of highly cross-linked PE. If longer follow-ups confirm the mechanical stability of highly cross-linked PE, ceramic heads might contribute additionally to the reduction of wear.

In conclusion we found significantly reduced wear for aluminumoxide heads compared to cobalt chrome heads which could be beneficial for young and active patients.