Correlations between spinal deformity and back muscle stiffness distribution

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Correlations between spinal deformity and back muscle stiffness distribution

 

Author: Cheng, Lok Kan
Title: Correlations between spinal deformity and back muscle stiffness distribution
Degree: M.Phil.
Year: 2017
Subject: Spine -- Muscles.
Muscle strength.
Muscle contraction.
Hong Kong Polytechnic University -- Dissertations
Department: Interdisciplinary Division of Biomedical Engineering
Pages: xix, 169 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2961686
URI: http://theses.lib.polyu.edu.hk/handle/200/8932
Abstract: Asymmetry of para-spinal muscle properties such as muscle activity, morphology and histology are often related to the etiology of idiopathic scoliosis (IS). Changes of these properties change can also lead to a change in muscle stiffness. However, very few studies attempted to investigate the para-spinal muscle stiffness distribution and asymmetry in either normal or IS population. Therefore, this study aimed to systematically document the para-spinal muscle stiffness distribution along and across the spine of normal subjects and idiopathic scoliosis subjects with objective indentation measurement. The significances of this study were to demonstrate if there was any para-spinal muscle stiffness imbalance existed in normal subjects and IS patients. In this study, a manual indentation system was developed and verified to perform muscle stiffness measurements. The system was comprised of a load cell and an electromagnetic spatial sensor to measure force applied to muscle and the subsequent deformation. Measurement results obtained were highly comparable with a standard mechanical testing machine (R²=.9903, p=.001) and had excellent intra- and inter- operator reliability (both ICC>0.9). Para-spinal muscle stiffness of normal subjects including male (n=13) and female (n=20) was measured separately at 1.5 cm (n=22) and 3 cm (n=11) contralateral to the spinous processes of T3, T7, T11 and L4 vertebral levels in relaxed standing. To test the system's repeatability, nine of the normal subjects underwent another measurement at the same locations of T3 and L4 one day after the first measurement. The measurements were reproducible (ICC >0.8). Para-spinal muscle stiffness measurement was also taken on IS subjects (n=25; male=7; female=18) separately at 1.5 cm (n=13) and 3 cm (n=12) contralateral to the spinous process of vertebrae at the level of upper end, apex and lower end of the largest curvature as well as the T3, T7, T11 and L4. Both the measurements on normal and IS subjects adopted the same protocol.
The average para-spinal muscle stiffness was found to be significantly larger along the left hand side of the normal spine (p<.05). The imbalance diminished when separation from spinous process increased from 1.5 cm to 3 cm. Muscle stiffness at T7 and T11 was demonstrated to be significantly larger than that at T3 and L4 in the normal subjects. Regardless of apex location in the scoliosis subjects, the muscle stiffness distributions between left and right side, along the spine and at different separations from spinous process were similar to the results of normal subjects. When para-spinal muscle stiffness of scoliosis subjects was analyzed according to the apex location, para-spinal muscles on convex side of the lumbar curve and on concave side of the thoracic curve were observed to have larger stiffness but did not show significant difference with the lateral side except at location of 1.5 cm at lower end of thoracic curve. Para-spinal muscle stiffness along lumbar curve gradually reduced from upper end towards the lower end. While along the thoracic curve, muscle stiffness increased then decreased with the largest value at the apex level. Para-spinal muscle stiffness at the same spine regions of the normal and scoliosis subjects were compared. Muscle stiffness at the concave side of the left lumbar curve was lower than the right lumbar spine of the normal spine while muscle stiffness at the concave side of the right thoracic curve was larger than the left thoracic of the normal subjects. The main findings of this study can be summarized as follows. First, average para-spinal muscle stiffness was larger on the left hand side of normal subjects in relaxed standing posture. Para-spinal muscle stiffness imbalance between left and right hand sides could be associated with a pre-existed vertebral rotation in the normal subjects but the cause of muscle stiffness change was uncertain. Second, para-spinal muscle stiffness imbalance observed across and along the spine in relaxed standing might be normal and irrelevant to the existence of scoliosis. Finally, inconsistent relationships between para-spinal muscle stiffness at concavity of different scoliosis apex locations and the same spinal region in normal spine suggested para-spinal muscles might play more than one role in the cause and development of scoliosis.

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