The purpose of this study is to evaluate the relative osseomechanical strength of a novel coated pin/screw in a clinical model.

The pin fixation and the risk for pin loosening and pintract infection is intimately connected Moroni et al., Magyar et al. Toksvig-Larsen and W-Dahl) The pin performance ratio for insertion to extraction torque (PPI) varies significantly between screw types.

The extraction torque force is the most important value and it is estimated that a removal torque around 300 Nm probably will be the best bon-pin fixation in clinical practice.

In animal studies and even in clinical studies the hydroxyapatite (HA) coated screw retained the highest level of osseointegration. However, the fixation for HAscrews is, especially in diaphyseal bone, the risk for too tight fixation, with extreme difficulties to remove the screws in few cases as a result ( high pain and seldom it is impossible to remove the screw) Coating by biphosphonate is a new novel technique with preclinical appealing performance, which theoretically should make this coating very appealing in clinical practice. The theory behind this technique is that it create a good pinfixation reasonable easy to remove.

The current most used cortical screw designs performed poorest in terms of fixation (PPI)

Method

Using the hemicallotasis technique for correction in high tibial osteotomies today, HA coated (Osteotite) conical 130/50 screws is used in the proximal tibia - the metaphysic - and plain (standard) cortical conical screws 110/40 is used in the diaphysis.

To study the effect of an improved pin coating a study including 30 patients randomised to the standard procedure today or the novel technique using biphosphonate coated screws.

In the metaphysic, the randomisation will be between the HA coated (Osteotite) screws and the biphosphonated coated screws 130/50 (screw thread 50mm) In the diaphysis the randomisation will be between the plain standard 110/40 screws and the biphosphonate 110/40 coated screws

Totally 30 patients will be studied which means totally 120 pins. This has been based on power calculations resulting in 23 patients in each group and calculated on extraction torque force. This is a clinical study and 30 patients is estimated due to expected drop out.

Inclusion Criteria:

• All patients which are diagnosed with arthr and needs an operation.