Biomechanical assessment and quantification of femur healing process using fibre Bragg grating strain sensors

Femur diaphysis fractures almost always require surgery to heal. The femur recovery process may take 3–6 months or even longer. The current femur recovery assessment methods are qualitative and mainly rely on physicians' clinical experience. A better methodology to quantify the healing status will help the physicians counsel their patients on the appropriate load-bearing activities accordingly. This paper numerically and experimentally demonstrates a femur healing assessment methodology using fibre Bragg grating (FBG) sensors. Finite Element (FE) analysis was conducted to confirm the feasibility of the used epoxies. For the experiments, a fourth-generation composite femur (4GCF) sample fixated with an implant plate was prepared. The sample was instrumented with a total of six FBGs on the proximal and distal posterior, mid-shaft, and implant surfaces. The prepared sample was then subjected to cyclic loading on a hydraulic tensile machine in various situations including (1) intact, (2) fractured (mid-shaft transverse and wedge), and (3) epoxy-healed. Epoxies with different curing times were applied on the fractured femur to mimic bone regeneration stages as they harden. FBGs were used to monitor the alterations in the strain values during the healing stages. The results demonstrated that the strain values measured by FBGs were able to justify the non-union, mal-union, delayed union, and fully union conditions on the femur shaft compared to the intact and fractured conditions. The proposed assessment technique can potentially be used on long bones with various fracture types and for patients of different ages and recovery rates.