Comparison of radiographic and pQCT analyses of healing rat tibial fractures

Fracture healing and callus formation have traditionally been evaluated by using X-ray radiography. Here we compared X-ray radiography and peripheral quantitative computed tomography (pQCT) in evaluating the healing callus of standardized tibial fractures in 141 female rats after a 4- or 8-week foll ow-up. The results were compared with the tensile (4-week) and compressive (8-week) failure load of the callus. The projectional size of callus, as de fined from lateral ex vivo radiographs, correlated significantly with the p QCT-defined cross-sectional area (CSA) of mid-callus. This relationship was dependent on the pQCT attenuation threshold, being higher for the CSA of c ompact bone (r = 0.85, P < 0.0001) than for the total bone CSA (r = 0.68, P < 0.0001). Radiographically defined callus projectional area also correlat ed strongly with bone mineral content (BMC) (r = 0.84-0.86, P < 0.0001). Th e mean optical density of the callus analyzed from the radiographs had only a weak correlation with the pQCT-defined bone mineral density (BMD) of cal lus. A weak negative relationship was found between CSA and BMD. The optica l density analyzed from lateral radiographs did not correlate with the tens ile or compressive failure load of callus. Callus size, BMC, and BMD were a ssociated with the compressive failure load, whereas both radiographs and p QCT were poor in explaining the failure load in tension.