# Evaluation of Bone Consolidation in External Fixation with an Electromechanical System
###### Abstract  
The monitoring of fracture or osteotomy healing is vital for orthopedists to help advise, if necessary, secondary treatments for improving healing outcomes and minimizing patient suffering. It has been decades since osteotomy stiffness has been identified as one main parameter to quantify and qualify the outcome of a regenerated callus. Still, radiographic imaging remains the current standard diagnostic technique of orthopedists. Hence, with recent technological advancements, engineers need to use the new branches of knowledge and improve or innovate diagnostic technologies. An electromechanical system was developed to help diagnose changes in osteotomy stiffness treated with the external fixator LRS Orthofix(r). The concept was evaluated experimentally and numerically during fracture healing simulation using two different models: a simplified model of a human tibia, consisting of a nylon bar with a diameter of 30 mm, and a synthetic tibia with the anatomical model from fourth-generation Sawbones(r). Moreover, Sawbones(r) blocks with different densities simulated the mechanical characteristics of the regenerated bone in many stages of bone callus growth. The experimental measurements using the developed diagnostic were compared to the numerically simulated results. For this external fixator, it was possible to show that the displacement in osteotomy was always lower than the displacement prescribed in the elongator. Nevertheless, a relationship was established between the energy consumption by the electromechanical system used to perform callus stimulus and the degree of osteotomy consolidation. Hence, this technology may lead to methodologies of mechanical stimulation for regenerating bone, which will play a relevant role for bedridden individuals with mobility limitations. external fixation; micromovements; bone callus; electromechanical system; bone consolidation +
Footnote †: journal: Medical Engineering
skin [1]. External fixation systems establish a link in the fragmented bone, allowing load transfer between the parts and promoting interfragmentary movements for bone healing [2]. The interfragmentary movement is the relative movement between the bone fragments, which can appear during a patient's weight-bearing activities. These micromovements in the fracture site are crucial to promoting bone callus growth and the control of bone regeneration [3]. Hence, the controlled physical activity of the patient might represent a mechanical stimulation that contributes to bone healing. Nevertheless, it is also worth stating that excessive mobility would disturb bone consolidation and perturb the healing process, leading to infections and bone misalignments [4; 5; 6]. Hence, these interfragmentary movements are crucial for the complex process of consolidating fracture [7]. Nevertheless, mechanical stimulation by patients' weight-bearing activities is only possible in people who can walk. In the case of bedridden patients or of those with reduced mobility, the bone union is more complicated and may even be inhibited by other health problems in the patients that might cause improper or impaired bone healing, leading to a significant increase in treatment time. Hence, all biomechanical devices that can introduce controlled micromovements at the fracture site, contributing to the rehabilitation of patients and reducing the recovery time, are an alternative to help those patients. According to [PERSON] and [PERSON] [8], the mechanical manipulation of the local fracture environment can significantly decrease fracture patients' healing time, suggesting that additional experiments should be conducted to determine the best parameters. For instance, it is necessary to know when the interfragmentary motion needs to be stopped to allow for consolidation and establish the best stimulation/rest ratio.