ABSTRACT
[Purpose] The purpose of this study was to study the correlation of knee range of motion between walking and squatting for young and elderly populations. [Subjects] Sixteen young and eight elderly healthy subjects were recruited for this study. [Methods] Three-dimensional joint motions of each subject were captured while they performed walking and squatting exercises. [Results] Significant differences in the non-sagittal plane knee motions (peak adduction, and peak external and internal rotation) were revealed between the young and the elderly during squatting. Correlations of three-dimensional knee range of motion between walking and squatting were positive and high in all three planes for the young subjects (R(2)=0.70, 0.52, and 0.45, respectively), but not for the elderly subjects (R(2)=0.23, 0.0004, and 0.05, respectively). [Conclusion] We suggest that changes in secondary knee kinematics and poor correlations between walking and squatting for the elderly may result from degeneration of the sensory and neuromuscular systems. It could be injurious for the elderly to perform high flexion activities.
ABSTRACT
OBJECTIVE: To study and establish the preliminary linear and modified models for the interface shear mechanics performance between implant and bone cement and to explore its damage significance. METHOD: The loosening research between artificial hip joint prosthesis stem and bone cement interface performance can be evaluated by the push-in test. Based on the debonding performance test, the analytical expressions of the average load and displacement from the debonding failure and splitting failure process were deduced and determined. The correlations of the expressions of the average load-displacement and statistical experimental data were analyzed. RESULTS: It demonstrated that the interface debonding failure mechanical model could be characterized as interface bond strength mechanical performance. Based on analysis of models and experimental data by the three statistical analysis methods, the results indicated the modified model could be better represented by the interfacial debonding strength properties. The bond stress τ and relative sliding s distribution along the embedment regional were coupling affected by both pressure arch effect and shear lag effect in bone cement. Two stress peaks of implant have been found at the distance from 0.175La loading tip to 0.325La free tip, which also verified the early loosening clinical reports for the proximal and latter region. As the bone cement arch effect, the bond stress peak tend to move to the free tip when the debonding failure would be changed into the splitting failure, which presents a preliminary study on the mechanism of early debonding failure for the stem-cement interface. CONCLUSIONS: Functional models of the stem-bone cement interfacial debonding failure are developed to analyze the relevant mechanism. The different locational titanium alloy stress, and the interfacial bond stress and the relative slides are evaluated to acquire a guide of the different positions of interfacial damage. The coupling effect which is original from the pressure arch and the interfacial shear hysteresis cumulative effect has influence on the interfacial debonding and damage process.
