Mechanical properties of callus in human tibial fractures: a preliminary investigation

Objective. Investigate the mechanical properties of callus in tibial fractu res treated with external fixation. In particular any time-dependent or non -linear characteristics. Design. A clinical-based investigative study. Background. A fracture bending stiffness, in the sagittal plane of 15 N m/d eg. has been stated as a satisfactory endpoint of clinical healing However using this criterion in 76 previous tibial fractures, four continued to a m alunion. Methods. Fracture properties were measured in clinic. The fixator was remov ed for the tests and a specially designed system was used to measure displa cement, and load. Fracture stiffness was measured in different planes and a t various loading rates. Passive stressing of the leg was performed whilst fracture displacement was recorded. A constant load was applied for a longe r period to assess creep properties. Results, Fracture stiffness was found to, vary between different planes of measurement and on load rate. The visco-elastic characteristics, of the cal lus changed with time. In, early, measurements, the callus absorbed a large proportion of energy when a load was applied. Later tests. showed a progre ssive change with the callus absorbing less energy. This demonstrates that the properties, of the callus changed with time, with the viscous element d iminishing and the elastic element increasing. This sometimes occurred with no change in the measured fracture stiffness. Conclusions. Further investigation is, needed, focusing on the visco-elasti c properties of callus, to develop a more reliable method of determining cl inical union.