Introduction The AO/ASIF 3.5 mm STS is increasingly used for internal fixation of large bones with the recent introduction of the 3.5 mm periarticular plating system. Our study aims to compare the insertion torque and mechanical properties of the screw after insertion into bovine femora using non tapped and pretapped methods.

Methods Three groups of ten 3.5 mm AO/ASIF STSs of variable lengths were used. One group was put aside as the control. One group was inserted into fresh bovine femora using pre-tapped drill holes and the final group using non-tapped drill holes. The insetion torques were measured and compared using an analogue torque screw driver. All screws were removed. The three groups were then tested for mechanical strength. The results of the groups were compared we found the insertion torque to be six times greater in the non tapped group compared to the pre tapped group. We noted the non tapped group failed later than the pre-tapped group, this was statistically not significant however. The mechanical strength of the screw was not statistically altered.

Conclusions We conclude that the 3.5 mm STS is easier to insert when pre tapped. However pre tapping is not necessary to preserve the mechanical strength of the screw.

Introduction: Osteochondral mosaic plasty is gaining popularity as a treatment for isolated chondral defects in femoral condyles. Most systems use a metal punch to impact the osteochondral grafts in pre-drilled defects. Damage to the chondrocytes during impaction grafting is of concern and new methods are being sort to minimise this deleterious effect.

This study was designed to see if using a plastic punch instead of a metal punch reduces the extent of chondrocyte damage in osteochondral mosaic plasty.

Method: Ten fresh sheep knees were used to harvest thirty osteochondral plugs using the COR system. The opposite condyles were then prepared to receive the osteochondral grafts. Ten plugs were impacted using a metal punch and ten using a plastic punch. The ten remaining plugs were used as controls. The plugs were then recovered and incubated for 24 hours prior to being stained with MTT. The stained cartilage was then photographed using a digital macroscope.

Images were interpreted using a graphics analysis programme.

Results: There was no significant difference in the extent of chondrocyte damage between the two groups. However, the extent of chondrocyte damage in the impacted groups was significantly greater than the control group.

Conclusion: Impaction grafting clearly damages chondrocytes of the osteochondral plug. In our study using a plastic punch did not reduce the extent of chondrocyte damage during mosaic plasty.

Introduction: Osteochondral mosaicplasty is gaining popularity as a treatment for isolated chondral defects in femoral condyles. Most systems use a metal punch to impact the osteochondral grafts in pre-drilled defects. Damage to the chondrocytes during impaction grafting is of concern and new methods are being sort to minimise this deleterious effect. This study was designed to see if using a plastic punch instead of a metal punch reduces the extent of chondrocyte damage in osteochondral mosaic plasty.

Method: Ten fresh sheep knees were used to harvest 30 osteochondral plugs using the COR system. The opposite condyles were then prepared to receive the osteochondral grafts. Ten plugs were impacted using a metal punch and ten using a plastic punch. The ten remaining plugs were used as controls. The plugs were then recovered and incubated for 24 hours before being stained with MTT. The stained cartilage was then photographed using a digital macroscope. The images were interpreted using a graphics analysis programme.

Results: There was no significant difference in the extent of chondrocyte damage between the two groups. However the extent of chondrocyte damage in the impacted groups was significantly greater than the control group.

Conclusions: Impaction grafting clearly damaged the chondrocytes of the osteochondral plug. In our study using a plastic punch did not reduce the extent of chondrocyte damage during mosaicplasty.