Mechanical properties of callus in human tibial fractures: a preliminary investigation.
OBJECTIVE
Investigate the mechanical properties of callus in tibial fractures treated with external fixation. In particular any time-dependent or non-linear characteristics.


METHODS
A clinical-based investigative study.


BACKGROUND
A fracture bending stiffness in the sagittal plane of 15 N m/deg. has been stated as a satisfactory endpoint of clinical healing. However using this criterion in 76 previous tibial fractures, four continued to a malunion.


METHODS
Fracture properties were measured in clinic. The fixator was removed for the tests and a specially designed system was used to measure displacement and load. Fracture stiffness was measured in different planes and at various loading rates. Passive stressing of the leg was performed whilst fracture displacement was recorded. A constant load was applied for a longer 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 callus changed with time. In early measurements, the callus absorbed a large proportion of energy when a load was applied. Later tests showed a progressive change with the callus absorbing less energy. This demonstrates that the properties of the callus changed with time, with the viscous element diminishing 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-elastic properties of callus, to develop a more reliable method of determining clinical union.


CONCLUSIONS
Improved understanding of the mechanical properties of callus could result in improved methods of measuring fracture healing.
Moorcroft
C I
CI
School of Engineering and Advanced Technology, Staffordshire University, P.O. Box 333, Staffordshire ST18 0DF, Beaconside, UK.ian.moocroft@staffs.ac.uk
Ogrodnik
P J
PJ
Thomas
P B
PB
Wade
R H
RH
D001696:Biomechanical Phenomena; D002146:Bony Callus / Q000503:physiopathology*; D004867:Equipment Design; D016267:External Fixators; D005592:Fracture Fixation; D017102:Fracture Healing / Q000502:physiology*; D006801:Humans; D013314:Stress, Mechanical; D013978:Tibial Fractures / Q000503:physiopathology* / Q000628:therapy