Ultrasound imaging of the thoracolumbar fascia in a wide range of people with and without lower back pain

Background: Lower back pain (LBP) is highly common; while most acute pain recovers within six weeks, 73% of people experience a re-occurrence at least once within 12 months [1]. The thoracolumbar fascia (TLF) has gained interest, particularly after an ultrasound-based study reported the TLF was 25% thicker and more disorganised in people with non-specific LBP (N=162) [2]. Differences in LBP were also found when Body Mass Index (BMI) was taken into account [3] This study aimed to examine the relationship between LBP status and TLF characteristics (thickness and echogenicity) while controlling for BMI.

Methods: The main study population consisted of N=154 participants, divided into a No LBP (NLBP) group (N=61) and an LBP group (N=93). The cohorts did not significantly differ in age, BMI, or physical activity levels . Ultrasound data collection utilised a Easaote, MyLab25Gold diagnostic ultrasound scanner with an LA435 4 cm linear transducer. B-mode scans were performed at 18MHz and 3 cm depth, using 58% Gain. Analysis focused on the thickness (pixels) and echogenicity (greyscale, 0–255) of the subcutaneous, perimuscular, and combined fascial layers.

Results: A straightforward relationship between LBP and echogenicity or thickness was not found when analysing overall group differences alone. However, significant differences were observed when considering the interaction with BMI. Significant Group x BMI interactions were found for the subcutaneous layer (p = 0.036) and the perimuscular layer (p=0.018). Specifically, thickness increased more significantly for the LBP group in the subcutaneous layer (2.74 pixels more) but increased less significantly for the LBP group in the perimuscular layer (2.31 pixels less). For echogenicity, a significant Group x BMI interaction was noted in the perimuscular layer (p=0.037), echogenicity generally decreased with BMI, but less so for the LBP group (3 points less).

Discussion and conclusion: The findings show that the relationship between LBP status and TLF measurements is complex and largely dependent on interactions with BMI. Crucially, the traditional metrics of echogenicity and thickness may not effectively measure the disorganisation in the tissues, which is an important, neglected factor. Morphological classification, using a scale (0=most disorganised; 10=most organised), proved highly reliable in a subsequent inter-rater reliability study [3], achieving 0.98 Cronbach’s alpha agreement among 30 clinicians. Therefore, the thoracolumbar fascia must be considered one of many players in LBP, suggesting future research should incorporate morphological features alongside traditional thickness and echogenicity measurements.