THE MEASUREMENT OF THE NON-LINEAR MECHANICAL PROPERTIES OF FRACTURED HUMAN TIBIAE DURING HEALING

It is widely accepted that the use of radiographs to assess fracture healing is, at best, misleading. It is also known that physical manipulation of the fracture can also produce misleading results. The determination of a fracture healing using a quantifiable rather than a qualitative assessment process is desirable for two reasons. Clinically, it avoids the premature or delayed removal of the treatment regime. In research it is required to better distinguish between treatment methodologies in comparative studies. The aim of this paper is to present the need for such a measurement and describe alternative methods that have been adopted. Further, a new device is presented that enables users to measure the linear and non-linear properties of healing callus with a high degree of certainty.

An initial trial of 21 patients with unstable diaphyseal tibial fractures was conducted. The patients had their fractures reduced using the Staffordshire Orthopaedic Reduction Machine and subsequently treated with an external fixator. From six weeks post treatment the progress of healing was assessed using manipulation, radiographs, fracture stiffness and multi-planar material property assessment. Fracture healing was deemed to have been obtained when a fracture stiffness in two planes was greater than 15 Nm/degree.

The paper presents results that demonstrate that the assessment of fracture healing using traditional manipulation and radiographs is erroneous. It will also demonstrate that the measurement of fracture stiffness can also be erroneous if loading rate is ignored. It further shows that fracture stiffness must be measured in two planes. Initial results examining principal stiffnesses will also be shown, along with the measurement of material properties based on work rather that stiffness.