Evaluation of low back muscle surface EMG signals using wavelets.

OBJECTIVE: To compare the ability of observers to correctly detect the reaction time of erector spinae response to unexpected load by inspecting nonprocessed electromyographic signals versus inspection of wavelet transformed electromyographic signals and versus automatic detection on the same wavelet transformed signals. BACKGROUND: Traditionally, electromyographic signal analysis is performed using Fourier transform based methods. However, muscle response to transients such as unexpected load, have limitations when using these methods of electromyographic processing. DESIGN: A comparison was made of the three methods using the same signals attained during sudden loading of the trunk. METHODS: 11 chronic low back pain patients and eleven normal subjects were investigated in sudden loading. Surface electromyographic signals were obtained from the erector spine muscle at L3. The ability of observers to detect reaction time of erector spinae muscle responses of nonprocessed electromyographic signals versus inspection of wavelet transformed electromyographic signals versus an automatic peak detection program was determined. RESULTS: The results have shown that the spine muscle reaction time was easier and more accurately determined in the wavelet domain rather than in its original signal representation. CONCLUSION: Wavelet transform methods improved the analysis of electromyographic signals in the time domain by facilitating the determination of the time of muscle activity. RELEVANCE: Wavelet transform could be a valuable tool for electromyographic analysis in resolving the psychophysical problem of perception involved in the analysis of nonprocessed signals. In clinical environments, where the speed and the accuracy of the analysis of electromyographic signal is critical, the wavelet based signal processing could be very important.

Evaluation of EMG signals from rehabilitated patients with lower back pain using wavelets.

This paper reports the preliminary results of an analysis of surface EMG signals obtained from rehabilitated patients with lower back problems using discrete wavelet transform techniques. In our study, 12 patients with lower back pain were tested before and after rehabilitation. The reaction time difference (before and after rehabilitation) from the erector spinae muscle caused by sudden loading was determined. The results indicated that the reaction time after rehabilitation was shorter than that before rehabilitation for about 45% of the tested cases.

Water content in human intervertebral discs. Part I. Measurement by magnetic resonance imaging.

Tension-relaxation experiments were performed on human disc lamellae specimens. The water content was found to affect the viscoelastic behavior and a master relaxation curve was constructed from the experimental data. The water content of disc phantoms is measured by magnetic resonance imaging (MRI) techniques. MRI was used to compare the discs of patients of different ages. The possibility of obtaining cross-sectional water distribution in human intervertebral disc material using MRI techniques and its relation to the disc's mechanical properties was explored, with the goal of constructing a realistic mathematical model of the disc which takes into account the water content of the disc.

Water content in human intervertebral discs. Part II. Viscoelastic behavior.

Water content of intervertebral discs is a significant aspect of both viscoelastic behavior and age-related degenerative changes. Using water content as a dependent variable, stress-relaxation was measured using standardized anulus fibrosus specimens strained at various levels of strain. Synthesis of experimental data into a master relaxation curve allows prediction of specimen response over time intervals not readily accessible experimentally. A quantitative understanding of the role of water content may have important clinical application, since magnetic resonance imaging is a tool which should allow water content determination in vivo.

A mechanical model for the human intervertebral disc.

Stress relaxation experiments were performed on specimens from a human intervertebral disc. Specimens were made from the nucleus pulposus and from the external lamellae of the anulus fibrosus in two different orientations. Tests were run with varying moisture content so as to develop a relaxation master curve. A model was developed based on the experimental data. It was found that the short term master curve for the lamellae of the anulus and nucleus are similar, whereas the long term rubbery plateau is different between the lamellae and the nucleus. It was also established that the master curves for different lamellae and the nucleus were shifted relative to each other in the time domain due to changes in water content. The average relaxation modulus of the whole disc was obtained by averaging the properties between the anulus and nucleus. This model was then used for studies of Schmorl's nodes, of degenerated discs and for circumstances in which hydration is considered to be important.

Digital image processing, a potential noninvasive technique in the diagnosis of diseased intervertebral discs.

The detection of the posterior edge of the L4-L5 intervertebral disc has been accomplished by applying digital image processing techniques on conventional lateral radiograms of the spine, and the method is described. The results of this study have shown that there can be substantial absorption at the site of the disc if the radiogram is properly taken; the existing information on the radiogram can be processed so that an improvement in the diagnostic quality of the radiogram can be achieved; and the edge of the posterior portion of the disc can be determined. This study, although a preliminary one, opens new possibilities for a safer and probably more accurate way of diagnosing herniated discs.