• bone stiffness
• external fixation
• fracture healing
• impact test
• resonant frequencies

One of the main limits of external fixation of fractured bone is the correct evaluation of the healing process to define correct times of fixator dynamization and removal, fundamental to avoid refractures. That requires a quantitative assessment of healing that unfortunately is not yet available in clinical practice.
The aim of the present study is to prove the feasibility and reliability of the vibrational method to assess fracture healing in case of external fixation, in in-vivo conditions. For the first time, fixator pins screwed into the bone were used to excite bone and to measure response, allowing to overcome the problem of soft tissues considered as the main limit of this approach.
A fracture tibia/femur treated with a monoaxial fixator after autogenous grafting, was monitored during healing over a 3/6 months interval. A series of impact tests were performed about every two or three weeks. Fracture healing was quantitatively assessed in terms of increase of resonant frequencies, that is related to bone stiffening.
Additionally, the method was applied to study the vibratory response of the leg after the removal of the fixator body (through pins), That provides some knowledge on human bone stiffness.
This study suggests the vibratory response of a fractured bone to be a valuable option for quantitative healing assessment. Its non-invasiveness allows a weekly monitoring that is currently not possible the traditional x-Rays. In the next future, a wide test campaign on humans will be carried out in order to identify indicators of different healing phases.