Symmetry in Paraspinal Muscles as a Predictor of the Development of Pregnancy-Related Low Back and Pelvic Pain: A Prospective Study

Abstract

Objective: To determine the asymmetry in the paraspinal muscle before pregnancy and evaluate its association with pregnancy-associated lumbopelvic pain (LPP).

Methods: This was a prospective case-control study conducted from January 2017 and December 2018. A total of 171 subjects (mean age ± SD, 27.4 ± 5.8 years) were finally divided into the LBP group, PGP group, and no LPP group. Each subject was asked to follow a standardized clinical imaging protocol before the pregnancy. The area of muscles (multifidus, erector spinae, and psoas muscles) on the axial slice at mid-disc of L₄ -L₅ and L₅ -S₁ were segmented and then the cross-sectional area (CSA) of a particular muscle was measured by outlining the innermost fascial border surrounding each muscle. The mean value of F-CSA's ratio to T-CSA (F/T CSA) was used to determine whether the bilateral paraspinal muscle was asymmetrical. Total muscle CSA (T-CSA) represents the sum of CSA of interested three muscles. The signal intensity can distinguish fat and muscle tissue in a different range. Based on this, functional CSA (F-CSA), represented by fat-free area, was evaluated quantitively by excluding the signal of the deposits of intramuscular fat. Total muscle CSA (T-CSA), functional CSA (F-CSA), and the ratio of F-CSA to T-CSA (F/T CSA) were measured unilaterally and compared between groups. Logistic regression was performed to determine the risk factors for pregnancy-associated LPP. The Pearson correlation coefficient was performed to test the relationship between asymmetry in F/T-CSA and pain rating.

Results: A total of 124 subjects (72.5%) (28.5 ± 5.2 years) had LPP during pregnancy. Forty-eight (38.7%) individuals had low back pain (LBP) and 76 (61.3%) had pelvic girdle pain (PGP). Seventy-six women (44.4%) were determined to have asymmetry in paraspinal muscle according to the definition in this methods section. The duration of follow-up was 24 months postpartum. A total of 39 (31.5%) women unrecovered from LPP. F/T-CSA was significantly decreased for LBP in the PGP group than in the and control group (0.03 ± 0.02 vs 0.05 ± 0.03 vs 0.12 ± 0.05, P < 0.001). Meanwhile, significant differences were detected in both groups (all P < 0.001). In patients with LBP, the level of paraspinal asymmetry, represented by the difference in F/T-CSA, was positively correlated with pain scores (r = 0.52, P < 0.01). However, no statistically significant correlation between pain scores and paraspinal asymmetry was found in PGP (r = 0.42, P > 0.05). Asymmetry in the paraspinal muscle (adjusted OR = 1.5), LBP (adjusted OR = 1.6), LPP in a previous pregnancy (adjusted OR = 1.4), sick leave ≥90 days (adjusted OR = 1.2), and heavy labor (adjusted OR = 1.2) were risk factors for the unrecovered LPP during pregnancy.

Conclusions: Asymmetrical muscular compositions could lead to abnormal biomechanics for the segmental motions. Lateral-directed physical training and stretching may help decrease the occurrence and severity of this condition.

Keywords: Asymmetry; Low back pain; Paraspinal muscles; Predictor; Pregnancy.