Changes in the cross-sectional area of multifidus and psoas in patients with unilateral back pain: the relationship to pain and disability.

Prospective, cross-sectional observational study. The aim of this study was to determine if there was an association between wasting of psoas and multifidus as observed on MRI scans and the presenting symptoms, reported pathology, pain, or disability of a cohort of patients presenting with unilateral low back pain. Current physiotherapy practice is often based on localized spine stabilizing muscle exercises; most attention has been focused on transversus abdominus and multifidus with relatively little on psoas. Fifty consecutive patients presenting to a back pain triage clinic with unilateral low back pain lasting more than 12 weeks were recruited. The cross-sectional surface area (CSA) of the muscles was measured. Duration of symptoms, rating of pain, self-reported function, and the presence of neural compression were recorded. Data analysis compared the CSA between the symptomatic and asymptomatic sides. There was a statistically significant difference in CSA between the sides (P < 0.001). There was a positive correlation between the percentage decrease in CSA of psoas on the affected side and with the rating of pain (rho = 0.608, P < 0.01), reported nerve root compression (rho = 0.812, P < 0.01), and the duration of symptoms (rho = 0.886, P < 0.01). There was an association between decrease in the CSA of multifidus and duration of symptoms. Atrophy of multifidus has been used as one of the rationales for spine stabilization exercises. The evidence of coexisting atrophy of psoas and multifidus suggests that a future area for study should be selective exercise training of psoas, which is less commonly used in clinical practice.