Microscopic changes in the multifidus muscle in people with low back pain associated with lumbar disc herniation

Lumbar disc herniation (LDH) is a common degenerative condition causing low back pain (LBP) due to nerve compression. Previous studies show conflicting findings regarding the multifidus (MF) muscle's microscopic changes in LDH patients. So, this study aimed to compare the affected MF to the adjacent MF on the ipsilateral and contralateral sides in LDH patients and examined correlations with clinical features of LBP. Four muscle biopsies were collected from each of 30 surgical participants. Immunohistochemistry was performed on tissue sections and imaged with an epifluorescence microscope. Data was analysed using a two-way ANOVA for muscle fibre cross-sectional area, perimeter, diameter, and composition, while pathological fibres were analysed using a one-way ANOVA. Pearson's correlation was employed to examine MF microscopy associations with clinical features. Results revealed no significant differences between the affected MF and MF from other sites, though significantly more pathological fibres were present in the affected MF (p < 0.05). A weak but significant negative correlation was found between type I fibres and LBP clinical features, though no such correlations were observed for type IIA fibres. In conclusion, LDH primarily impacts the pathological status of the MF rather than fibre phenotype or size, and severity of clinical features is associated with the size of type I fibres.