Fracture stiffness measurement using the orthometer: reproducibility and sources of error

Objectives. To elicit the reproducibility and the common sources of error in the use of the Orthometer, a commercially available goniometer based system, designed to measure the stiffness of healing fractures. Design. A laboratory based study. Background. The Orthometer is widely used to measure the progress of fracture healing in a quantitative manner. It has been shown previously that the bending stiffness of a fracture increases with healing and that a stiffness of 15 Nm/degree equates with the functional union of a tibial fracture. Methods. The Orthometer was attached in a standard manner to nylon bars of known stiffness to determine the accuracy of the device. The Orthometer was then set up with changes in a single positional variable to assess the effect of this variable on the measurement accuracy. A number of different clinicians were asked to use the Orthometer before and after a simple training session and any improvements in the measurement accuracy were observed. Results. Stiffness could be measured to within 10% or less of the true stiffness. Markedly different degrees of error were introduced with the various set-up variables. A simple training session improved clinician accuracy. Conclusions. Although the Orthometer does allow some degree of safety margin, it is essential that set-up is performed carefully, and that the clinician has been trained in the use of the device.