The reliability of plain radiography in experimental fracture healing

Objective. To investigate the reliability of radiographs in the evaluation of healing of closed fractures. Design. A closed midshaft tibial fracture was created in 40 goats and stabi lized with an external fixator. The animals were assigned to four groups: n o inject-ion, injection of I mg osteogenic protein-1 (OP-1), 1 mg OP-1 with collagenous carrier, or carrier alone. Radiographs were performed weekly u ntil the animals were killed after 2 and 4 weeks. Healing was evaluated usi ng radiographs, biomechanical testing, and histological examination. All ra diographs were examined by two independent observers. Interobserver agreeme nt was calculated and radiographic scores were compared with mechanical and histological scores using regression analysis. Results. Regression analysis showed poor correlation between radiographic s cores and biomechanical and histological data. Correlation coefficients var ied between 0.39 and 0.63. Good agreement between the observers was seen in only three parameters: visibility of the fracture line, weightbearing abil ity, and a combined healing parameter. Conclusion. Plain radiography provides poor parameters for monitoring the f racture healing process.