The Mechanical properties of Vastus Medialis and Vastus Lateralis in Subjects with Patellofemoral Pain Syndrome
Date Issued
2008
Date
2008
Author(s)
Chen, Han-Yu
Abstract
This dissertation was designed to investigate the mechanical properties of the vastus medialis and the vastus lateralis in patients with patellofemoral pain syndrome. In this dissertation, the mechanical properties indicated the electromechanical delay and the viscoelasticity of the tendon structures of the vastus medialis and the vastus lateralis. From the literature review, the measurements for the electromechanical delay and viscoelasticity of the vastus medialis and the vastus lateralis were questionable. Hence the study was divided into three stages for three purposes. n the first stage, the electromechanical delay of the vastus medialis and vastus lateralis is determined by measuring the interval between the time of onset of muscle activities and the time of onset of mechanical output. However, individual mechanical output of the vastus medialis and vastus lateralis cannot be obtained with the conventional method because of regarding the knee extension force as the mechanical output. Therefore, the objective of this stage study was to develop a new method for measuring the electromechanical delay of the vastus medialis and vastus lateralis individually. Twelve healthy volunteers participated in the experiment. The motor point of the target muscle was electrically stimulated to evoke a muscle twitch. Simultaneously, the electrical stimulation signal was transmitted to ultrasound apparatus via the electrocardiography input channel. The ultrasound apparatus was used to capture the patellar movement elicited by the muscle twitch. The electromechanical delay was measured from the onset of the electrical stimulation to the onset of patellar movement. The results showed that the intra-class correlation coefficients for the reproducibility of the electromechanical delay measurements of the vastus medialis and vastus lateralis were greater than 0.8. The electromechanical delay of the vastus medialis and vastus lateralis were 18.3 ± 2.2 ms and 24.8 ± 5.8 ms, respectively. This new method provides a more precise measurement of the electromechanical delay in the vastus medialis and vastus lateralis than does the conventional method because of the use of patellar movement as the mechanical output. n the second stage, twelve patellofemoral pain syndrome patients and twelve healthy subjects with gender, age, height and weight matched were recruited to participate to the study. The new method was applied to all the subjects and the resultant electromechanical delay of the vastus medialis and vastus lateralis were compared between these two groups. The result of this stage study was demonstrated that the percentage of people whose the electromechanical delay of vastus medialis being larger than that of vastus lateralis in subjects with patellofemoral pain syndrome are significantly greater than those in healthy individuals. According to the result, we speculated that the mechanical properties of vastus medialis and vastus lateralis might have adaptive changes in patients with patellofemoral pain syndrome. n the third stage, we further investigated the relationships of the length of electromechanical delay and the viscoelasticity of musculature. Previous scholars believed that the time taken for the stretching of the series elastic component by the contractile element is considered a major portion of electromechanical delay. Therefore, the viscoelasticity of the series elastic component is related to the length of electromechanical delay. The area of load-unload loop is an index of hysteresis and related to the viscoelasticity of tendon structures. Therefore, the area of load-unload loop of the vastus medialis and vastus lateralis was measured and compared between healthy individuals and patellofemoral pain syndrome patients. The elongation of the tendon structures is one part to form the load-unload loop. In previous studies, however, the measurement of the elongation of tendon structures is questionable due to the displacement of the tendon structures of vastus lateralis being measured. We would like to modify the previous method to measure the more precise elongation of the tendon structures of vastus medialis and vastus lateralis. The isokinetic dynamometer was used to provide the resistance during subject performing ramped isometric knee extension exercise; simultaneously, the muscle activities of the vastus medialis and vastus lateralis were detected by the electromyography recording system. Besides, the elongations of the tendon structures of the vastus medialis and vastus lateralis during ramped isometric contraction were captured by the B mode ultrasonography. A customized switch was used to synchronize the signals of muscle activity and the ultrasonography. The results of this stage study were showed that the percentage of people whose the area ratio of hysteresis loop of vastus medialis being larger than that of vastus lateralis in subjects with patellofemoral pain syndrome are significantly greater than those in healthy individuals. According to the result, we speculated that the viscoelasticity of vastus medialis and vastus lateralis might have a change in patellofemoral pain syndrome patients. The greater energy loss of vastus medialis contraction in daily activity and the decreased speed of muscle force transmission in patellofemoral pain syndrome patients. Consequently, the electromechanical delay of vastus medialis is smaller than that of vastus lateralis and that might deteriorate the abnormal patellar tracking.
Subjects
electromechanical delay
viscoelasticity
tendon structures
ultrasonography
load-unload loop
patellofemoral pain syndrome
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