Telemetric assessment of bone healing with an instrumented internal fixator

Abstract

In an interdisciplinary project involving electronic engineers and clinicians, a telemetric system was developed to measure the bending load in a titanium internal femoral fixator. As this was a new device, the main question posed was: what clinically relevant information could be drawn from its application? As a first clinical investigation, 27 patients (24 men, three women) with a mean age of 38.4 years (19 to 66) with femoral nonunions were treated using the system. The mean duration of the nonunion was 15.4 months (5 to 69). The elasticity of the plate-callus system was measured telemetrically until union. Conventional radiographs and a CT scan at 12 weeks were performed routinely, and healing was staged according to the CT scans. All nonunions healed at a mean of 21.5 weeks (13 to 37). Well before any radiological signs of healing could be detected, a substantial decrease in elasticity was recorded. The relative elasticity decreased to 50% at a mean of 7.8 weeks (3.5 to 13) and to 10% at a mean of 19.3 weeks (4.5 to 37). At 12 weeks the mean relative elasticity was 28.1% (0% to 56%). The relative elasticity was significantly different between the different healing stages as determined by the CT scans. Incorporating load measuring electronics into implants is a promising option for the assessment of bone healing. Future application might lead to a reduction in the need for exposure to ionising radiation to monitor fracture healing.

Implantable microelectromechanical sensors for diagnostic monitoring and post‐surgical prediction of bone fracture healing

“…Similar patterns of decreasing implant strain magnitude during the healing cascade have been observed via telemetric assessments of internal femoral fixator in humans, telemetric assessments of internal intramedullary nails in humans, wired external fixators in sheep, telemetric assessment in femoral replacements in humans, fixation plates with a wired strain gages in sheep, and wired external fixators in humans . These studies support the contention that significant changes in osteosynthesis stiffness during the acute healing phase (days 1–30) transpire well before radiographic observations (i.e., plain radiographs and coronal CT images) of calcified tissue can be obtained.…”

Utilizing Multiple BioMEMS Sensors to Monitor Orthopaedic Strain and Predict Bone Fracture Healing

“…Measurements from the present study suggest a decrease in load share experienced by implant hardware as fracture stiffness increases. Previous studies have exhibited similar trends through a variety of testing methods including the use of wired external fixators in humans and sheep, wired strain gauges on fixation plates in sheep, and telemetric assessment of femoral IMNs in humans . These findings are further supported by a previous study by our group, through the use of a single BioMEMS sensor on fixation plates in sheep, which found decreasing implant strain throughout the healing process.…”

Temporal delimitation of the healing phases via monitoring of fracture callus stiffness in rats

“…Therefore, it would be possible to determine whether the delay in the healing time induced by blunt‐chest trauma in our previous study results either from a prolonged repair phase analogous to more flexible fixation or from a delayed start of the repair phase with the same duration. The method described in this animal study can also be used for the characterization of the repair phase in humans if in‐vivo data for the patient is available. This may help to earlier identify clinical cases in which the healing outcome is critical, and would be more reliable than being based on x‐ray images solely .…”