Aims

Hereditary haemochromatosis is a genetic disorder that is caused by several known mutations in the human homeostatic iron regulator protein (HFE) gene. Abnormal accumulation of iron causes a joint disease that resembles osteoarthritis (OA), but appears at a relatively younger age and is accompanied by cirrhosis, diabetes, and injury to other organs. Increased serum transferrin saturation and ferritin levels are known markers of haemochromatosis with high positive predictive values.

Introduction: The aim of this study was to evaluate direct mechanical measurements from an external fixator as an alternative method to DEXA to examine the healing progress of patients undergoing distraction osteogenesis (DO).

Methods: Five patients were evaluated concurrently by BMD estimates and direct mechanical measurements from an external fixator to examine bone consolidation approximately every six weeks after the end of distraction. For mechanical measurements, all rods were removed from the external fixator and replaced with three load cells. An axial load of 10 kg was applied to the tibia and the load recorded from the three load cells was used to calculate the proportion of the load supported by the fixator (Load Share Ratio, LSR), which indicates the stiffness of the newly developed bone.

Results: The LSR decreased significantly for all patients (r2=0.63, p < 0.01), indicating increased bone stiffness. DEXA based BMD estimates decreased for two of five patients despite normal healing progress and likewise BMD and LSR were weakly correlated (r2=0.22, p > 0.05).

Discussion: Bone consolidation is often accompanied by changes in bone geometry, which can make DEXA based BMD estimates inaccurate for this application. Mechanical measurements from external fixators are not subject to this error and therefore could be a more reliable method to evaluate the healing progress of patients undergoing DO.

Conclusion: Direct mechanical measurements from an external fixator may be an alternative procedure to improve the evaluation of healing progress during DO.