Correlation of pQCT bone strength index with mechanical testing in distraction osteogenesis

Abstract

Distraction osteogenesis is an established method of treatment of non-unions and limb length discrepancies. Despite improvements in surgical techniques and fixation devices there is still a considerable possibility of failure of the regenerate bone after frame removal. The hypothesis of the present experimental study was that a noninvasive bone strength marker, the strength-strain index (SSI) measured by peripheral quantitative computerized tomography (pQCT), could be significantly correlated with a biomechanical bone strength index, the maximum load at bone failure (Fmax), assessed in a three-point bending test. The right tibias of fifteen male New Zealand White rabbits were subjected to gradual lengthening using an external fixator. At the end of the consolidation phase (55th day) the animals were sacrificed and the lengthened tibiae were collected free of soft tissue, after removal of the lengthener, for immediate scanning and mechanical testing. The values of cortical bone mineral density, cortical bone area, and the corresponding SSIy, as measured by pQCT, were assessed for statistically significant correlation relative to the values of the Fmax and stiffness as evaluated by the three-point bending test were assessed. SSIy showed a statistically significant positive correlation with the maximum load (Fmax) with a correlation value R = 0.846 (p < 0.001), and it was a good predictor of Fmax since it was able to describe the 71.6% of variability of Fmax(R2 = 0.716). Furthermore, cortical bone area appeared to be highly correlated with Fmax (p < 0.005), but it was a less efficient predictor of Fmax (R2 = 0.471). There was, also, a statistically significant correlation between SSIy and bone stiffness as assessed in the 3-point bending test (p < 0.005). In conclusion, the present study reveals that the SSI can be used as a sensitive index of adequate consolidation of the regenerate bone, possibly able to reduce mechanical failure due to premature frame removal. In clinical relevance, the aforementioned hypothesis should be applied in studies of human populations and possible confirmation of its validity would establish pQCT as a valuable diagnostic tool not only in distraction osteogenesis but also in other techniques of bone healing. © 2009 Elsevier Inc. All rights reserved