Use of ultrasound shear wave imaging in understanding low back pain

Abstract

Low Back Pain (LBP) is one of the commonest musculoskeletal disorders. One of the major clinical problems with LBP is the lack of objective diagnostic tools. Conventional imaging modalities are found ineffective as abnormalities found in patients with LBP also appear in asymptomatic subjects. The reason for this may be due to the altered anisotropic nature of muscle and the limitations of traditional imaging tools that provide only structural information. This thesis aims to enhance understanding through using ultrasound shear wave imaging which can measure the stiffness value of the tissue in different postures.

A scanning protocol was first standardized for the abdominal muscle and back muscle. A quality map was added during the data analysis to remove unwanted noise. The effect of the quality map was examined using an elasticity phantom. Compared to the data analyzed without using a quality map, the proposed method could reduce the occurrence of outlier.

The standardized protocol was applied in patients with LBP and healthy subjects to understand the differences between them. The LBP group had a greater variation in the thickness of the abdominal muscle and shear modulus of multifidus, and smaller average value of the shear modulus of abdominal muscle than the healthy group. There was a significant difference in the asymmetry ratio of the shear modulus of internal oblique with muscle contraction. Healthy subjects had better positive correlation of abdominal muscle between resting and contracted states, and between the left and right sides than the patients but the LBP group had positive linear relationship between thickness and shear modulus of abdominal muscles. These suggested that there were differences between the two groups in both structure and biomechanics properties. Future studies are suggested to change the abdominal muscle contraction exercises and add a back muscle contraction exercise. Pain score should also be studied to understand the relationships among thickness, shear modulus, and pain.

To evaluate the effect of LBP rehabilitation exercise, ultrasound shear wave imaging was applied. Over the 40-day-study period, the effects varied and suggested the effect of the exercise depends on muscle condition. The immediate effect brought by the exercise was reduced by the muscle recovery ability. Muscle asymmetry was found in structure only but not in the mechanical property. The result suggested that the effect of the rehabilitation exercise was not uniform. The study period should be elongated in the future studies as the effect of the rehabilitation exercise was not significant in the back muscle.

To conclude, ultrasound shear wave imaging is able to measure the shear modulus of tissue in different body postures and was applied in two studies to understand the differences of muscle biomechanical properties between patients with LBP and healthy groups and evaluate the effect of LBP rehabilitation exercise.