Biomechonical evaluation of vibrotactil feedback for bone anchored prostheses

BACKGROUND. Vibrotactil feedback is one of the ways how humans receive information about the body and other subject conditions. There are a number of mechanisms providing a sensation of vibration, including lamellar bodies. Osseoperception phenomenon is well known from the oral implantation experience. The nature of osseoperception is still unclear. However, only a few studies can be found in the literature regarding osseoperception in osseointegrated prostheses and the rule of vibration in this process.
AIM. Biomechanical options of using vibratory oscillation of rehabilitation devices for biological feedback. The main purpose of the study is an investigation of oscillations in the parts of the bone-anchored prosthesis and their influence on the intramedullary implant and residual bone.
METHOD. Ten proximal femurs were used. Intramedullar stem to anchor above-knee prosthesis was implanted. All samples got cemented fixation. The system residual femur, intramedullar stem, above knee prosthesis were created. All samples were tested in a load machine. 10, 20… 80 kg of vertical loading was provided. During the loading, the prosthesis got vibration stimulation with the help of a standard mini-shaker (type 4810). The stimulation range was from 5Hz to 500Hz (0.5Hz step). Feet and knee joints got vibration stimulation separately. Vibration measurement was performed by a 3D laser vibrometer. Vibration was measured on multiple points: bone surface, uncovered stem surface, prosthetic surface.
RESULTS. Oscillation resonances were detected for all samples. Range of resonances was form 30Hz – 80Hz. The lowest frequencies were found for minimum loading. An increase in prosthesis loading increases the frequency of resonance. The amplitude of oscillations shows a revert correlation. The maximum amplitude of oscillation corresponds to the minimum load. An increase in loading decreases amplitude. Vibrational stimulation of prosthetic foot reduces the amplitude of oscillation and works as a shock absorber in comparison with stimulation of knee joint. No other significant resonances were found on the level of 200Hz – 300Hz. Amplitude has not changed significantly by load increasing. The above mentioned frequencies correspond to sensitiveness of lamellar bodies.
DISCUSSION AND CONCLUSION. Vibrational oscillations of the prosthesis are spread on the residual femur surface. Oscillation amplitude is sufficient for inducting the action potential of mechanical receptors. The natural frequency of the above-knee prosthesis is between 30 – 80 Hz. Range of frequency 200Hz – 300Hz does not have an evident maximum of oscillations. This is an optimal range of sensitiveness of lamellar bodies. It may be used for artificial generated vibration for improving rehabilitation devices feedback.