The aim of this study was to compare the lateral abdominal muscle thickness and cross-sectional area of multifidus between individuals with and without scoliosis. Previous research demonstrated that abdominal and multifidus muscle thickness is decreased in patients with low back pain compared to their healthy peers. In a study conducted by Zapata et al, deep paraspinal muscle thickness (T8, L1, and L4 levels) were compared between teenagers with and without idiopathic scoliosis (24). Results showed that muscle thickness in all three levels were higher at the concave side in subjects with scoliosis, compared to the healthy subjects, which is in line with the findings in the current study (24). They also reported an increased muscle thickness at the concave side of patients with scoliosis compared to the convex side in both T8 and L1 levels (24). This finding was not consistent with the results of the current study and this difference might be might be attributed to some methodological differences between the two studies such as different sample size, age difference between participants of the two studies, as well as different multifidus levels of assessment. In the current study the L5-S1 level was studied and, in the study conducted by Zapata et al, the L1 and L4 levels were investigated.
Kim et al, assessed the activity of the transverse abdominus muscle in maximum exhale, and compared the results between patients with chronic low back pain and healthy controls (25). Results demonstrated that although transverse abdominus muscle thickness was different in both resting and contraction in patients with chronic back pain compared to the controls, muscle activation changes were not significantly different. Also, the level of atrophy of the transverse abdominus muscle in patients with chronic back pain was variable. Observed differences in muscle thickness and activation of transverse abdominus in this group of patients might be due to possible changes in movement pattern and not necessarily in the excitability of motor neurons (25). Pain can affect muscle activation and may result in movement control impairments. Therefore, the morphologic changes in transverse abdominus muscle, might be responsible for the beginning of movement control impairments and subsequent back pain (25).
In a study by Whittaker et al, carried out on patients with and without Lumbo-pelvic pain, abdominal muscle (TrA, IO, EO, and rectus abdominus) thickness and surrounding soft tissue were assessed using ultrasonography. Only the rectus abdominus muscle thickness was shown to be significantly less in patients with lumbo-pelvic pain compared to the healthy controls (26). This finding was not consistent with current results, which might be due to the fact that patients experienced low back pain (due to scoliosis) in this study compared with acute low back pain of those in Whitaker et al, study.
Wallwork et al, investigated lumbar multifidus muscle size during contraction, as well as the ability of the muscle for maximum voluntary isometric contraction, using ultrasonography in subjects with and without back pain (27). They reported a significantly smaller cross section area for multifidus muscles at L5 level in patients with back pain compared to the healthy controls. They also reported that the percentage of muscle thickness during contraction was significantly less in low back pain patients compared to the healthy controls (27). Similarly, Hides et al, reported significant decrease in cross sectional view of the multifidus muscle at the L4-L5 level in patients with back pain compared to the healthy controls, which was accompanied by an increase in the maximum asymmetry at L5 level in patients with unilateral pain (28).
Previous findings demonstrated that abdominal and lumbar multifidus muscle thickness as well as muscle activity is decreased in patients with low back pain and those with scoliosis compared with healthy subjects.