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Monitoring the healing of long bones has been studied extensively to reduce the period of encumbrance and unnecessary pain for patients suffering from fractured bones. This is more critical for unstable fractures in the pelvis as the patients can bedridden for up to 12 weeks to allow proper healing to take place. Current methods employed to monitor long bone healing are insufficient for applications in the pelvis as the human pelvis presents a significant change in geometry which demands a different approach. This paper explores an approach where vibration analysis is used to provide in-situ monitoring of a healing fracture in a human pelvis. Experimental tests were conducted on 4th generation synthetic pelvises instrumented with an array of PZT sensors. The synthetic pelvises were cut at the sacrum to simulate a fractured pelvis followed by the application of araldite epoxy to simulate healing by allowing the epoxy to cure. Measurements were collected from the sensor array over the curing period to obtain the transfer functions (TFs) for various excitations. An impact hammer was utilised to obtain powerful broadband excitations while the PZT sensors were used to detect the response in the synthetic pelvis as a results of these excitation signals. A comparison of TF against cure time (healed amount) indicates the presence of a significant relationship with the stiffness recovery of the epoxy at the cut of the synthetic model.

Having unstable sacral fractures requires patients to be bedridden for a significant period of time for healing to take place without complications. This causes severe muscle atrophy, along with blood circulation problems in older patients. It is therefore highly beneficial to fast-track weight-bearing activities to reduce these complications by monitoring the recovery of the fracture. Past experimental work shows that dynamic response of a fixated synthetic (fourth-generation composite sawbone) pelvis is affected by the change in stiffness at the fracture location. The changes in this dynamic response can be observed by placing sensors on the pelvis and on the fixation. However, placing sensors on the pelvis is not practical. The aim of this article is to report on a set of computational investigation on the potential of placing sensors on the fixation to determine the stiffness restoration of the fractured region of the pelvis. This work will focus on the Denis I fracture, where the fracture is located in the sacrum. The ability to relate the dynamic response of a particular section of the fixation that is remote to the fracture location will have significant implication in the extending structural health monitoring concept to determine the state of healing of a fractured pelvis. A fourth-generation composite sawbone pelvis was used in the work reported in this article.

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