Subcutaneous fat index: a reliable tool for lumbar spine studies

Objectives Obesity has been proposed as a risk factor for low back pain (LBP), and the body mass index (BMI) has been used for obesity; however, a more reliable tool is required to assess obesity-related health issues. A recent study depicted the subcutaneous fat tissue thickness (SFTT) at the L1–L2 level as superior to BMI in predicting LBP and spine degeneration. However, the study failed to answer the following questions: (1) What was the cutoff value for the SFTT to predict LBP and spine degeneration? (2) Could this new index be adjusted according to gender? (3) Could this new index predict fatty infiltration in the paraspinal muscles, severe intervertebral disk degeneration (IVDD), and Modic changes in the lumbar spine? Therefore, the current study aimed to answer these questions by developing and validating a new anthropometric index—the subcutaneous fat index (SFI). Methods This study retrospectively reviewed the magnetic resonance imaging database of patients with LBP and compared them with asymptomatic volunteers. Results Appropriate cutoff values for females and males were 8.45 mm and 9.4 mm, respectively. Females and males with the SFI of > 8.45 mm and > 9.4 mm, respectively, had significantly higher rates of spine degeneration. Conclusion The SFI reliably distinguished patients with LBP from the asymptomatic subjects and could reliably distinguish patients with severe IVDD/Modic changes at the lower lumbar levels and those with moderate-to-severe fat-infiltrated paraspinal muscles at all lumbar levels with reliable cutoff values for males and females. Key Points • The subcutaneous fat tissue thickness at L1–L2 level (subcutaneous fat index [SFI]) was superior to BMI in predicting LBP and spine degeneration. However, a reliable cutoff value has not been previously defined. • The subcutaneous fat index had reliable cutoff values of 8.45 mm and 9.4 mm for females and males, respectively. • Females with an SFI of > 8.45 mm and males with > 9.4 mm had significantly higher rates of severe IVDD, Modic changes, and fatty infiltration in their paraspinal muscles.