In disc herniation, lower back pain (LBP) and disability occur because the disc material presses on the dorsal and/or ventral nerve roots (Yazar and Altun, 2007, Yelmaiza et al., 2022). The pain and limitation of movement caused by disc herniation causes labor loss and incurs treatment costs worldwide, with an annual average treatment cost of over $100 billion in United States of America alone (Katz, 2006). The progression of disc herniation is an important factor affecting muscle degeneration/atrophy (Noonan and Brown, 2021). The most affected muscles are the lumbar stabilizer muscles of the spine. The lumbar stabilizer muscles of the spine are the erector spinae (ES), the multifidus (MF), the quadratus lumborum (QL), and the psoas major (PM). These muscles play an important role in the proper functioning of the spine and load distribution by resisting shear forces on the lumbar spine during posture and walking (Rickenbacher et al., 2013). Neuromuscular reeducation of these muscles that stabilize the spine is the basis of conservative treatment of disc herniation. Therefore, it is important to investigate how these muscles are affected by disc herniation.

Previous studies have examined the paraspinal, MF, and PM muscles in disc herniation (Hansen et al., 2006, Kjaer et al., 2007, Meakin et al., 2013, Sun et al., 2017). The PM, QL, small rotator, and intertransversarii muscles also contribute to stabilization by connecting to the lumbar vertebrae; however, very little research has been performed on these muscles. Among these less frequently investigated muscles, two studies have evaluated the PM (Dangaria and Naesh, 1998, Stanuszek et al., 2021), while a systematic review conducted in 2021 reported that the QL lumborum muscle was less studied in the literature (Noonan and Brown, 2021). Demonstrating with MRI technology how disc herniation, the lumbar lordosis angle, and patient age affect the lumbar stabilizer muscles will contribute to conservative treatment approaches in disc degeneration and guide clinicians and researchers.

To the best of our knowledge, this study is the first to compare the muscle groups that stabilize the lumbar spine in individuals with disc herniation and healthy (asymptomatic) individuals by grouping patients according to age range and herniation level. The aim of this study was to investigate factors affecting the PM, QL, MF, and ES muscles, which stabilize the lumbar spine in cases of disc herniation.