Twenty years experience in fracture healing measurement with strain gauges

The external fixator provides a mechanical connection between the bone fragments and recording devices or power systems. We have used this characteristic of external fixation since 1965 to record deformations occurring at the fracture site and to measure the mechanical characteristics of fracture healing in more than 500 patients. As in all osteosyntheses, the fixation material (here the external rod) resists the mechanical forces applied to the bone fragments. As healing progresses, the bone participates more and more in the weight bearing of the system and the rod deforms less. Seven types of deformation curves have been defined, characterizing seven different modes of healing: 1) normal healing, 2) slow healing, 3) delayed union, 4) arrest in evolution, 5) pseudarthrosis, 6) resorption of the callus, and 7) breakage of the callus.