PAPER 3: A NEW MODEL TO STUDY METAPHYSEAL FRACTURE HEALING UNDER CONTROLLED BIOMECHANICAL CONDITIONS

Abstract

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.