Introduction: Misalignment of total knee replacement components is one of the reasons for early loosening and revision surgery. Several studies have shown that using CAS (computer assisted surgery) there is a more precise positioning of the implants. So far only studies have reported about the costs of CAS. The aim of this retrospective study was to evaluate the cost of CAS for an orthopaedic unit.

Method: For analysing the costs per operation we had to include the hip resurfacing procedures as for this operative procedure CAS is used. We therefore included in our retrospective analysis 200 TKR (100 CAS, 100 conventional) as well as 60 hip resurfacing operations (30 CAS, 30 conventional). We recorded the operation time, costs for single use material, costs for man power and the leasing costs for the CAS unit.

Results: The operation time in the CAS group was prolonged (average 15 minutes). This produced extra costs of 75€. Single use equipment costs were calculated with 89€/operation. The leasing costs were 290€/operation. There was less blood loss in the CAS group with a reduced need for transfusion saving 12€/operation. Including costs for operation staff and the leasing costs we had overall costs of 442€/operation in comparison to the conventional operated group. The rate of complications was not increased using CAS.

Conclusion: Using CAS our orthopaedic unit had to spend 442€/operation for using this technique. We obtained a better alignment of the implants in both CAS groups (knee and hip) and had less blood loss. Still there is no proof that better alignment will reduce the rate of revisions and will increase the lifetime of implants.

The aim of our study was to investigate whether placing of the femoral component of a hip resurfacing in valgus protected against spontaneous fracture of the femoral neck.

We performed a hip resurfacing in 20 pairs of embalmed femora. The femoral component was implanted at the natural neck-shaft angle in the left femur and with a 10° valgus angle on the right. The bone mineral density of each femur was measured and CT was performed. Each femur was evaluated in a materials testing machine using increasing cyclical loads.

In specimens with good bone quality, the 10° valgus placement of the femoral component had a protective effect against fractures of the femoral neck. An adverse effect was detected in osteoporotic specimens.

When resurfacing the hip a valgus position of the femoral component should be achieved in order to prevent fracture of the femoral neck. Patient selection remains absolutely imperative. In borderline cases, measurement of bone mineral density may be indicated.