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BACKGROUND: The main reason for the postoperative loosening of cemented prosthesis is interfacial debonding and bone cement internal damage. Most studies have suggested that both of them occur in the process of fatigue damage, however, little is reported on primary loading that results in the initial damage to the bone cement-stem interface and inside of bone cement. OBJECTIVE: To study the mechanical properties of bone cement-stem interface, and the effect of crack formation in bone cement on interfacial loosening. METHODS: The cement-titanium al oy handle implant components were prepared. The maximum adhesive force of bone cement-stem interface was measured using push-in experiment. The cement damage and crack in the process of bone cement-handle interfacial debonding were monitored online using acoustic emission tester. The non-destructive testing on the metal surface and the inner layer of bone cement cylinder was conducted using three-dimensional surface profiler, ultrasonic microscopy and X-ray detector. RESULTS AND CONCLUSION: The online monitoring results of debonding experiment and acoustic emission tester demonstrated that the initial damage of bone cement initiated in the primary loading of patients after operation, rather than at fatigue damage stage. Bone cement coffin caused cracks initiation mainly due to the combination effect of radial and axial stress. The bone cement-stem interfacial shear lag effect could not prevent the gradual extension of interface and inner coffin crack from top to bottom. The bone cement defects formed in solidification process was likely to affect the mechanical properties of the material, and eventual y induced the crystal face and macromolecular chain fractures, forming silver striated cracks and leading component failure.
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BACKGROUND: Human lower limb system under different motion statuses exhibits great difference in terms of kinetic characteristics and joint deformation magnitude. Total hip replacement has been shown to be the best method to solve the severe illness of hip joints today. A good understanding of the responses of human lower limb system, in particular the knee joint, following total hip replacement is significant for rehabilitation training of patients.OBJECTIVE: To analyze the effects of total hip replacement on knee joint deformation during motions by comparing the data collected from a patient who underwent total hip replacement 19 months ago and a healthy control subject under the same testing environment and method.METHODS: The patient was measured through the use of Optotrak Certus motion capture system (Northern Digital Inc.,California), and simultaneously measurements were performed in a healthy control subject presenting with similar body weight and body mass. Measurement indices included step length, step frequency, joint corner, and joint displacement curves. Speed and acceleration of each joint were calculated based on measured data.RESULTS AND CONCLUSION: Following total hip replacement, the structure of natural hip joint was destroyed. Although the gait did not change greatly, experimental data showed that knee joint deformed more greatly than normal gait, indicating the self-accommodation of human body, i.e., increasing the loading and deformation magnitude of knee joints can avoid the injuries caused by hip joint surgery.
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To investigate the influence of temperature and humidity on skin friction property and to unveil the mechanism therein involved, a test of friction coefficient for four volunteers was carried out on a multi-specimen friction tester. The temperature and humidity of skin were measured with infrared temperature instrument and dermohygrometer. The results showed that the fluidity and ductility of skin were affected by the change of skin temperature. The skin temperature decreasing friction coefficient and the normal displacement decreased first, and then remained unchanged, deformation friction and adhesive friction being the major underlying mechanism. Humidity significantly affected the skin friction properties. The friction coefficient increased with the increasing of humidity. When skin humidity reached to 42% or so, the friction coefficient increased to 1.0 and higher. Meniscus effect was noted to be the major cause of moist skin surface with high friction coefficient.
Subject(s)
Adult , Female , Humans , Male , Young Adult , Body Water , Physiology , Friction , Humidity , Skin , Metabolism , Skin Physiological Phenomena , Skin Temperature , Surface PropertiesABSTRACT
Objective To study effects of hydrated rate on compressed deformation properties of natural articular cartilage.Methods The mass losses of pure cartilage,subchondral bone and cartilage sample were measured under different volatilization time with constant vacuum temperature container of 40 ℃,and confined compressed deformation of different hydrated rates was measured using UMT-2 multi-specimen test system.Combined with cartilage structural equation originated by Mow,the aggregated modulus and permeability of cartilage tissue were obtained.Results The mass losses of pure cartilage,subchondral bone and cartilage sample functioned with a non-linear ascending relation with volatilization time in the environmental temperature of 40 ℃.The volatilization time for different hydrated rates of 75%,50%,25%and 0% was 17 min,35 min,54 min and 100 min,respectively.Higher hydrated rate produced more compressed deformation,lower aggregated modulus and higher permeability.Conclusion The viscoelastic mechanisms of flow-dependence and flow-independence are manifested by compressed deformations while the aggregated modulus and permeability could quantitatively depict the mutual relation between hydrated rate and compressed deformation.