Serial Strain Gauge Measurement of Bone Healing in Hoffmann® External Fixation

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Abstract
In order to better assess callus strength for postoperative management of Hoffmann external fixation patients, the author attempted to estimate the amount of strain when bending or compressing the fracture site with a strain gauge glued to the middle of a connecting rod. Calculations in a computer architectural model of a plane beam structure show that the amount of strain on a connecting rod would decrease hyperbolically when the mechanical properties of the callus increased. Strength testing in a cadaveric crural bone confirms the importance of callus volume. The serial strain gauge measurement technique was applied to a series of 23 cases treated with Hoffmann external fixation, 20 of which achieved bone healing. On the basis of the bone healing curve obtained with the strain gauge measurements, the healing process is classified into five types.