Ultrasound Measures of the Abdominal Wall in Patients with Low Back Pain Before and After an 8‐week Lumbar Stabilization Exercise Program, and Their Association With Clinical Outcomes

Background Lumbar stabilization exercise programs (LSEPs) act positively on clinical outcome measures in patients with low back pain (LBP), but the underlying mechanisms are not well understood. Among the various neuromuscular mechanisms, a good candidate is better activation of the abdominal wall, as measured with rehabilitative ultrasound imaging (RUSI). Objectives To determine whether RUSI measures are (1) sensitive to LBP status and treatment (LSEP) and (2) correlate with clinical outcomes following the LSEP. Design An exploratory one-arm clinical trial with healthy participants as a control group. Setting LSEP was delivered in a clinical setting; outcomes were measured in a laboratory setting. Participants Thirty-one patients with nonacute LBP and 30 healthy controls. Methods Outcome measures were performed before and after an 8-week LSEP in patients with LBP, and with the same time interval for control participants to compare with patients at baseline. Main outcome measurements Pain, disability, as well as static (at rest) and dynamic (percent thickness change) RUSI measures for abdominal muscles (transversus abdominis, internal oblique [IO], and external oblique [EO]). Results Patients did not produce systematic changes in RUSI measures relative to controls, even if patients had significant improvement in pain and disability. However, the correlational analyses between the absolute change (pre- to post-LSEP) (1) of EO and IO thickness (in mm) at rest (bilaterally), and (2) in pain following the LSEP were significant and consistent (range: .36-.45) in patients. Conclusions Although positive clinical improvements were observed following LSEP, there were minimal systematic changes in RUSI measures, likely because patients were not different from controls at baseline. Correlational analyses, however, indicated that greater reductions in pain were associated with reduced thickness of the EO and IO following the LSEP, suggesting the presence of some heterogeneity (or clinical subgroups) among the patients. Level of evidence II.