Introduction: Lateral callus distraction can be used to treat bone defects and increase bone diameter. However, this requires longitudinal splitting of the bone, which can be avoided by a new method.

Material and Methods: Twenty sheep were operated at the medial site of the tibia. After drilling 1 mm holes into the medullary cavity, a titanium plate with a hydroxyapatite coating was attached to the bone surface using a custom-made device

After 10 days this device was distracted 0.3 mm, twice a day until a distance of 6 mm was achieved (n=10). In the control group (n=10), the titanium plate was adjusted to a distance of 6 mm. All sheep received fluorescence labeling. 10 weeks p. o., bone formation underneath the titanium plate was investigated using pQCT, x-ray and histomorphology.

Results: In the distraction group there was 5 times more newly formed bone. > Bone columns bridging the space between the cortex and titanium plate were found. In the first 30 days, the bone formation was significantly enhanced in the distraction group as indicated by the fluorescent labeling

Conclusion: A strain induced bone formation is not only possible between two bony surfaces created by an osteotomy, but also between a bony surface and an appropriately designed implant. This new method allows for bone apposition in a large number of bones, which could not be properly treated in the past.

Introduction: Metaphyseal fracture healing is seldom studied and models used so far do not control the biomechanical conditions in the healing area. The aim of this study was to develop a new standardized and biomechanically adjustable osteotomy gap in an animal model.

Material and Methods: A pilot study with two sheep was performed. An incomplete osteotomy was created in the retro patellar region of the distal femur. The compression forces of the patella lead to a cyclic reversible reduction of the 3 mm osteotomy gap size. This inter-fragmentary movement (IM) can be limited by a steel implant fitted into the proximal osteotomy gap. After 8 weeks the sheep were sacrificed and the healing studied by x-ray and histology.

Results: The osteotomy gap, which allowed 0.3 mm IM showed woven bone bridging in the whole gap. The sheep with 1 mm IM showed only partial bone formation but mainly fibrous tissue and fibrous cartilage. There was no external callus formation.

Discussion: This new model allows the study of metaphyseal bone healing under various biomechanical conditions. Even though metaphyseal healing is different from diaphysical callus healing, IM appears to have a similar effect, leading to direct bone formation under stable condition and enchondral ossification under high IM.