Multifidus muscle size and percentage thickness changes among patients with unilateral chronic low back pain (CLBP) and healthy controls in prone and standing.

The aim of this study was to determine if differences exist in lumbar multifidus (LM) thickness at rest and during activation, between individuals with chronic low back pain (CLBP) and controls. Lumbar multifidus thickness was assessed via rehabilitative ultrasound imaging (RUSI), and was performed in prone and standing both at rest and during muscle activation i.e. with a contralateral arm lift (CAL). Twenty participants were assessed; ten CLBP participants and ten controls. Rehabilitative ultrasound imaging was used to measure LM thickness and percentage thickness change at L4/L5 and L5/S1 in four positions; prone at rest, prone during activation with a CAL, standing at rest, and standing during activation with a CAL. Independent and paired t-tests were used to calculate differences in LM thickness and percentage thickness change between groups, and also between sides in the CLBP group. There was a significant difference in LM percentage thickness change in standing during activation with a CAL; the CLBP demonstrated a greater percentage thickness increase at L5/S1 compared to the controls, (p = 0.05). There were no differences between groups at the L4/L5 level for this position. There were no differences between the groups for LM thickness or percentage thickness change in prone or standing at rest, or during activation with a CAL in prone. Within the CLBP group, no significant between side differences were found. These results give preliminary insight into possible differences in LM contractile behaviour during functional movements in CLBP, however, larger scale research is warranted.