A fracture movement monitoring system to aid in the assessment of fracture healing in humans

Abstract

This paper presents a new design for a device to monitor the motion of fracture fragments in diaphyseal tibial fractures. The device measures the motion that occurs at the fracture site when loaded by gait or by manipulation. It has undergone rigorous calibration and acceptance trials. The device has been used in ethically approved research clinics held at the North Staffordshire Hospital (40 patients). The paper presents a selection of results obtained using the new device. The results demonstrate several new ways of assessing fracture healing by examining fracture site motion. The following conclusions were drawn: 1. If fracture monitoring devices are to be attached to bone screws, it is essential to minimize bone screw errors. To do this, each patient must have similar bone screw lengths, orientations, alignment and siting. This is only achievable using a peroperative reduction device. 2. If fracture stiffness is to be used as a measure of fracture healing, load rate should be controlled; at the very least strain rate should be controlled. 3. It is imperative that fracture stiffness be measured in more than one plane by a biplanar device so that asymmetry may be accommodated. 4. Fracture stiffness, on its own, is probably not a sufficiently rigorous measure of healing end-point. The quantifiably viscoelastic properties of healing callus should be taken into account.

Biomechanics of Fracture Healing

“…Multiple noninvasive approaches to measuring callus stiffness, whether in axial loading or bending, have been reported, and the clinical feasibility of several has been demonstrated. Typically, these measurements rely on measuring the displacement across the fracture gap or the pin-to-pin displacement under a known force or bending moment [17][18][19] . If an external fi xator is present, it is necessary to consider only the fraction of the applied load that is borne by the callus as opposed to the fi xator.…”

An automated system for measuring multi-dimensional, time dependent mechanical properties of a human tibial fracture

“…This system relies on the patient being treated with external fixation; the fixation bone screws being used to mount the transducer system. If the bone screws are not loose and the transducer system is flexible in comparison to the screws then the measurement will accurately represent the fracture site motion [2,15,18]. Furthermore, to ensure that measurements are reproducible, consistent bone screw configuration was achieved by reducing the fracture prior to fixation.…”

“…The electrical output from the transducers were signal conditioned using proprietary signal conditioners and their respective outputs fed into the data acquisition/load control system. The system was calibrated using the technique presented by Ogrodnik et al [15]. The goniometers and load cell were calibrated individually and as integral components of the measurement system.…”

“…[11][12][13][14] presented the development of systems to monitor fracture site motion for external fixators. Recently Ogrodnik et al [15] presented a multi-dimensional system to measure fracture site movement that occurs under manual loading. The results of the paper demonstrated that the measurement of fracture stiffness, alone, to determine a endpoint of fracture healing may well be erroneous due to the non-linearity of the callus mass and the inherent effects of load-rate on any measurement.…”

“…A monitoring system, similar to that in ref. [15] is also presented. The device has been used in limited clinical studies.…”