In a consecutive prospective series of 104 tibial shaft fractures, the strength at the site of union was observed by a noninvasive technique at regular intervals. Eighty-one patients were male and 23 were female. Six fractures were open, and 13 patients had multiple injuries. The primary treatment was conservative with cast immobilization in 86 patients, external fixation by a quadrilateral system in 14, and open reduction and internal fixation in four. A measure of the strength of union is obtained by calculating a quotient between induced deflection between the fracture fragments and the applied bending moment. By plotting this quotient against time-since-injury, a curve describing the changes in stability can be constructed. With this curve it is possible to define united fracture and normal union, and the differentiation between delayed union and true nonunion is possible. Time-to-union in all 104 patients was 16 +/- 15.2 weeks. In 14 with delayed union, surgical measures intended to promote union could be avoided because repeated measurements indicated progressive increase in stability. Bone grafting was performed in 13 fractures for treatment of nonunion. Statistical analysis based on objective measurement of stability failed to identify a specific factor responsible for delayed union or nonunion.

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