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Item type:Publication, Access status: without files , Vibro-acoustic and nonlinear analysis of cadavric femoral bone impaction in cavity preparationsOwing to an ageing population, the impact of unhealthy lifestyle, or simply congenital or gender specific issues (dysplasia), degenerative bone and joint disease (osteoarthritis) at the hip pose an increasing problem in many countries. Osteoarthritis is painful and causes mobility restrictions; amelioration is often only achieved by replacing the complete hip joint in a total hip arthroplasty (THA). Despite significant orthopaedic progress related to THA, the success of the surgical process relies heavily on the judgement, experience, skills and techniques used of the surgeon. One common way of implanting the stem into the femur is press fitting uncemented stem designs into a prepared cavity. By using a range of compaction broaches, which are impacted into the femur, the cavity for the implant is formed. However, the surgeon decides whether to change the size of the broach, how hard and fast it is impacted or when to stop the excavation process, merely based on acoustic, haptic or visual cues which are subjective. It is known that non-ideal cavity preparations increase the risk of peri-prosthetic fractures especially in elderly people. This study reports on a simulated hip replacement surgery on a cadaver and the analysis of impaction forces and the microphone signals during compaction. The recorded transient signals of impaction forces and acoustic pressures (≈ 80 µs–2 ms) are statistically analysed for their trend, which shows increasing heteroscedasticity in the force-pressure relationship between broach sizes. TIKHONOV regularisation, as inverse deconvolution technique, is applied to calculate the acoustic transfer functions from the acoustic responses and their mechanical impacts. The extracted spectra highlight that system characteristics altered during the cavity preparation process: in the high-frequency range the number of resonances increased with impacts and broach size. By applying nonlinear time series analysis the system dynamics increase in complexity and demand for a larger minimum embedding dimension. The growing number of resonances with similar level of the transfer function indicates a higher propensity to dissipate energy as sound; the change in embedding dimension indicates a decrease in linearity. The spectral changes as well as the embedding dimension changes indicate either an improved coupling between the bone and the broach or the onset of micro-fractures caused by growing stress levels within the bone.Publicationtype: Journal Article22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Vibro-acoustic and nonlinear analysis of cadavric femoral bone impaction in cavity preparations(EDP Sciences, 2018-02-02); ; ; ; Owing to an ageing population, the impact of unhealthy lifestyle, or simply congenital or gender specific issues (dysplasia), degenerative bone and joint disease (osteoarthritis) at the hip pose an increasing problem in many countries. Osteoarthritis is painful and causes mobility restrictions; amelioration is often only achieved by replacing the complete hip joint in a total hip arthroplasty (THA). Despite significant orthopaedic progress related to THA, the success of the surgical process relies heavily on the judgement, experience, skills and techniques used of the surgeon. One common way of implanting the stem into the femur is press fitting uncemented stem designs into a prepared cavity. By using a range of compaction broaches, which are impacted into the femur, the cavity for the implant is formed. However, the surgeon decides whether to change the size of the broach, how hard and fast it is impacted or when to stop the excavation process, merely based on acoustic, haptic or visual cues which are subjective. It is known that non-ideal cavity preparations increase the risk of peri-prosthetic fractures especially in elderly people. This study reports on a simulated hip replacement surgery on a cadaver and the analysis of impaction forces and the microphone signals during compaction. The recorded transient signals of impaction forces and acoustic pressures (80 μs - 2 ms) are statistically analysed for their trend, which shows increasing heteroscedasticity in the force-pressure relationship between broach sizes. Tikhonov regularisation, as inverse deconvolution technique, is applied to calculate the acoustic transfer functions from the acoustic responses and their mechanical impacts. The extracted spectra highlight that system characteristics altered during the cavity preparation process: in the high-frequency range the number of resonances increased with impacts and broach size. By applying nonlinear time series analysis the system dynamics increase in complexity and demand for a larger minimum embedding dimension. The growing number of resonances with similar level of the transfer function indicates a higher propensity to dissipate energy over sound; the change in embedding dimension indicates a decrease in linearity. The spectral changes as well as the altered dimension requirements indicate either an improved coupling between the bone and the broach or the onset of micro-fractures caused by growing stress levels within the bone.Publicationtype: Conference PaperScopus© Citations 7 470 293 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Towards the understanding of hip squeak in total hip arthroplasty using analytical contact models with uncertainty(2016-08-21); ; ; ; Osteoarthritis in hip joints affects patients' quality of life such that often only costly orthopaedic surgeries i.e. total hip arthroplasty (THA) provide relief. Common implant materials are metal alloys, steel or titanium-based, plastics such as ultra-high molecular weight polyethylene, or biocompatible alumina and composite ceramics. Hard-on-hard (HoH) bearing articulations, i.e. ceramic-on-ceramic, or hard-on-soft combinations are used. HoH implants have been known to suffer from squeaking, a phenomenon commonly encountered in friction-induced self-excited vibrations. However, the frictional contact mechanics, its dynamics related to impingement, the effect of socket position, stem configuration, bearing size and patient characteristics are poorly understood. This study gives an overview of the state of the art biomechanical research related to squeaking in THA, with a focus on the effects of friction, stability, related wear and lubrication. An analytical model is proposed to study the onset of friction-induced vibrations in a simplified hemispherical hip stem rubbing in its bearing by varying the contact area. Preliminary results of the complex eigenvalue analysis and stick-slip motion analysis indicate that an increased contact fosters the development of instabilities, even at very small values of the friction coefficient owing to large local contact pressures.Publicationtype: Conference Paper43