Non-invasive Vibrational Assessment Of Bone Fracture Healing

Abstract

In this paper we present the results of an animal bone fracture study which attempts to relate the vibrational response of a healing limb to its mechanical stiffness. Tibial osteotomies are performed on nine rabbits which are sacrificed at different stages of healing. Vibrational measurements are acquired from the healing fractured limb and the contralateral intact limb. The frequency domain vibrational admittance function is estimated using an electromechanical shaker and force and acceleration transducers. A feature known as the energy ratio (ER) derived from the admittance function estimates of both the fractured and intact limbs is used to characterize the strength of the healing fracture relative to the intact value, obtained using a biomechanical torsional test. Results indicate a strong correlation between the ER and relative stiffness of the fractured to intact limb. Vibrational measurements from three human clinical fracture patients over several weeks is also presented. A feedforward neural network scheme is also described for classifying the vibrational data. INTRODUCTION Bone fractures are the most common injury treated by orthopaedic surgeons. Treatment typically consists of immobilization of the fracture site until normal weightbear- ing can resume, i.e., until return of normal stiffness and strength values. Techniques for assessment of bone fracture healing currently consist of radiographic and clinical evalua- tions. Uncertainty regarding the significance of radiological findings may result in unnecessarily long periods of immobiliz- ation. The challenge to develop a reliable bone strength measurement during fracture healing has led several inves- tigators to apply low frequency (50 Hz-2 kHz) vibrational energy techniques (1,21. These previous attempts have not. however, related the vibrational response to healing fractured bone strength, and thus have not achieved any degree of use in orthopaedic practice. The objective of the present study was to develop a vibrational fracture healing assessment method which could overcome limitations of previous approaches, and thus provide orthopedists with a clinical tool for accurate and quantitative strength estimates during fracture healing.