Vibration reponse analysis in orthopaedics and its application at the lumbar spine

Vibration response analysis has been carried out on human lumbar spines in-vitro and in-vivo. Random vibration in the frequency range between 20 Hz and 2 kHz was applied to the L5 spinous process in the antero-posterior direction while motion response was measured at the other spinous processes of the lumbar spine. Transfer mobility which defines the lumbar spine's motion response to vibratory force was evaluated by using the fast Fourier transform and spectral averaging technique. There was high damping during the in-vitro tests and the lumbar spine was found to behave as a segmented beam hinged at the thoracic and sacral ends. Fundamental mode shape was observed at frequencies lower than 150 Hz and this pattern was also observed with simulated fusion of the facet joints and interbody fusion. Mobility summated for the whole range of frequency could be modelled by an exponential expression. Useful parameters have been identified and they were found to relate to the lumbar spine's vibratory characteristics resulting from structural modifications. Vibration testing performed on normal subjects revealed that a relaxed lumbar spine was highly damped and non-resonant. First flexural vibration mode was observed only under the action of the back extensors. Averaged figures have been established for the coefficients of an exponential expression which fits closely to the summated mobility curve. The mobility and its attenuation coefficients in different frequency bands have been evaluated from twelve normal subjects. Localized attenuation of vibration response and the reduction in mobility were observed on a patient with osteoporotic lumbar spine. Mobility in the low frequencies was reduced while the medium and high band mobility were enhanced in patients with postero-lateral fusion and instrumentation for fixation of the lumbar spine. The attenuation pattern of these patients was consistent, and corresponded to the existence of structural enhancement.Vibration response analysis has been carried out on human lumbar spines in-vitro and in-vivo. Random vibration in the frequency range between 20 Hz and 2 kHz was applied to the L5 spinous process in the antero-posterior direction while motion response was measured at the other spinous processes of the lumbar spine. Transfer mobility which defines the lumbar spine's motion response to vibratory force was evaluated by using the fast Fourier transform and spectral averaging technique. There was high damping during the in-vitro tests and the lumbar spine was found to behave as a segmented beam hinged at the thoracic and sacral ends. Fundamental mode shape was observed at frequencies lower than 150 Hz and this pattern was also observed with simulated fusion of the facet joints and interbody fusion. Mobility summated for the whole range of frequency could be modelled by an exponential expression. Useful parameters have been identified and they were found to relate to the lumbar spine's vibratory characteristics resulting from structural modifications. Vibration testing performed on normal subjects revealed that a relaxed lumbar spine was highly damped and non-resonant. First flexural vibration mode was observed only under the action of the back extensors. Averaged figures have been established for the coefficients of an exponential expression which fits closely to the summated mobility curve. The mobility and its attenuation coefficients in different frequency bands have been evaluated from twelve normal subjects. Localized attenuation of vibration response and the reduction in mobility were observed on a patient with osteoporotic lumbar spine. Mobility in the low frequencies was reduced while the medium and high band mobility were enhanced in patients with postero-lateral fusion and instrumentation for fixation of the lumbar spine. The attenuation pattern of these patients was consistent, and corresponded to the existence of structural enhancement