Treatment of juxta-articular comminuted fractures with dislocated fragments of long bones are difficult for intramedullar interlocking nails. The question is can the results be improved by a modified interlocking nail. The Synthes UHN was prepared by 7 additionally bore holes displaced for 90 degrees. This modified implant contains a total of 12 interlocking points in different directions. The biomechanical testing showed a maximal reduction of the bending strength of 35 % for the modified nail. It seems to be dependent from the orientation of the bending stress. The modified nail with unreamed technique was implanted in the tibial bone of the sheep. This was carried out after segmental osteotomy with/without an additionally interlocking third fragment. 8 weeks postoperatively in 75 % of all cases a consolidation in the sense of fracture healing could be seen. The none used bore holes of the modified nail were penetrated with active osteogenetic tissue. Our results should be compared with the findings of the bone conduction chamber. The aplicability of our model for experimental osteological studies will be discussed.
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