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.

Introduction: The Donjoy OA Orthesis has been developed to treat unicompartimental osteoarthrosis of the knee joint. The idea is to reduce the load in the affected joint compartment. Sofar only clinical evaluations and gait analysis have been published. The aim of this study is to use intraarticular pressure sensors in an anatomical model to work out the existing intraarticular pressures.

Method: 5 fresh non fixated anatomical knee models were used. The models were prepared leaving the 2/3 of the femur as well as the tibia and fibula. We used a right and left-sided version of the Donjoy OA Orthesis. A defined pressure was applied via the pressure application screw.

The dorsal capsule of the knee joint was opened and the meniscus were mobilised in a way that the pressure foils (Fuji typ super low) could be placed between the undersurface of the meniscus and the tibia plateau in each joint compartment. The measurements were recorded in four different joint positions (0°, 30°, 60° flexion and 0° with removed meniscus).

Each anatomical model was well fixed in a universal testing machine” (Instron, System ID: 5565 H1703). The used axial pressure in all set ups used was 1500N.

We used 4 four different test series:

no pressure, no orthesis

no pressure, with orthesis

with pressure, no orthesis

with pressure, with orthesis

After removing the pressure foils the actual pressure could be estimated by the diameter of the coloured foil. Using the programm Mortphomet it was possible to calculate these pressure areas and give procentual figures.

Results: The Antivarus Orthesis could reduce the intraarticular joint pressure between 55–70%

Without pressure:

Knee → 64,37 %

Knee → 55,30 %

Knee → 54,43 %

Knee → 58,75 %

Knee → 44,80 %

Mean value 55%.

With pressure:

Knee → 74,59 %

Knee → 74,00 %

Knee → 67,91 %

Knee → 86,34 %

Knee → 49,69 %

mean value 70%.

The Antivalgus Orthesis could reduce the intraarticular joint pressure between 46–74%

Without pressure:

Knee → 79,78 %

Knee → 76,22 %

Knee → 75,20 %

Knee → 62,55 %

Knee → 76,49 %

Mean value 74%.

With pressure:

Knee → 42,68 %

Knee → 46,24 %

Knee → 64,61 %

Knee → 40,08 %

Knee → 37,20 %

Mean value 46%.

Conclusion: This anatomical investigation has proved for the first time via intraarticular pressure measurements that it is possible to considerable reduce the intraarticular pressure using the Donjoy antivarus and antivalgus Orthesis.