A Novel Capacitive Measurement Device for Longitudinal Monitoring of Bone Fracture Healing.

Angela Sorriento,Paolo Dario,Marcello Chiurazzi,Gastone Ciuti,Luca Fabbri,Michelangelo Scaglione

doi:10.3390/s21196694

Abstract

The healing process of surgically-stabilised long bone fractures depends on two main factors: (a) the assessment of implant stability, and (b) the knowledge of bone callus stiffness. Currently, X-rays are the main diagnostic tool used for the assessment of bone fractures. However, they are considered unsafe, and the interpretation of the clinical results is highly subjective, depending on the clinician’s experience. Hence, there is the need for objective, non-invasive and repeatable methods to allow a longitudinal assessment of implant stability and bone callus stiffness. In this work, we propose a compact and scalable system, based on capacitive sensor technology, able to measure, quantitatively, the relative pins displacements in bone fractures treated with external fixators. The measurement device proved to be easily integrable with the external fixator pins. Smart arrangements of the sensor units were exploited to discriminate relative movements of the external pins in the 3D space with a resolution of 0.5 mm and 0.5°. The proposed capacitive technology was able to detect all of the expected movements of the external pins in the 3D space, providing information on implant stability and bone callus stiffness.

Highlights

Fracture healing is a complex and dynamic process, which involves both biological and mechanical aspects
We propose a low-cost and customised solution composed of a 2D matrix of capacitive sensors that are able to detect both the relative translation and the rotations of the external fixator pins, as an index for determining the bone’s healing status
We developed and tested in Ansys® a finite element model (FEM) model of the bone–external fixator system to investigate the relative pins displacements due to the applied compressive loads

Summary

Introduction

Fracture healing is a complex and dynamic process, which involves both biological and mechanical aspects. A non-union fracture occurs if the reparative processes end before the bone union takes place. The positioning of an external fixator is faster and simpler [6] and, it allows the dynamic adjustment of the degree of mechanical rigidity of the implant during the healing process. Successful treatment with an external fixator is strongly dependent on the identification of the correct timing for its removal. Premature removal of the fixator can lead to bone refracture, resulting in additional surgical procedures and an extended period of hospitalisation. On the other hand, delayed removal of the implant leads to an unnecessarily prolonged treatment time [7]. Prevention and an adequate healing assessment are essential factors for both the patient’s well-being and to reduce the costs associated with surgical re-interventions and follow-ups

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Discussion

Conclusion