The Trendelenburg sign is a common clinical finding indicating hip abductor dysfunction and altered pelvic stability. The relationship between the Trendelenburg sign, spinopelvic biomechanics, hip muscle strength, and lumbar magnetic resonance imaging (MRI) abnormalities remains insufficiently understood. This study aims to investigate the association between Trendelenburg sign positivity and lumbar MRI findings, including facet arthropathy, ligamentum flavum hypertrophy, multifidus muscle morphology, and psoas muscle characteristics, as well as spinopelvic biomechanical parameters and hip abductor muscle strength.

The Trendelenburg sign is a clinical indicator of hip abductor muscle dysfunction and altered pelvic stability. Changes in hip abductor function may affect spinopelvic biomechanics and contribute to lumbar degenerative changes. This prospective observational study aims to investigate the association between Trendelenburg sign positivity and lumbar MRI abnormalities in adults with chronic low back pain.

Participants will be classified as Trendelenburg-positive or Trendelenburg-negative based on clinical examination. Hip abductor muscle strength and lumbar MRI findings will be evaluated. MRI parameters will include the presence and severity of facet joint arthropathy, ligamentum flavum thickness, multifidus muscle thickness, and psoas muscle characteristics.

The primary objective is to determine whether a positive Trendelenburg sign is associated with lumbar facet arthropathy. Secondary objectives include evaluating the relationships between the Trendelenburg sign, hip abductor strength, and other lumbar MRI parameters. The findings may improve understanding of the biomechanical relationship between hip function and lumbar degeneration in patients with chronic low back pain.

Inclusion Criteria:

• Age between 18 and 65 years.
• Patients who have previously presented to the clinic with a complaint of low back pain.
• Willingness and ability to provide written informed consent for participation in the study.
• Availability of lumbar MRI images obtained within the previous 12 months and accessible for evaluation.

Exclusion Criteria:

• Presence of red flag conditions associated with low back pain, including malignancy, infection, acute trauma, or significant neurological deficits.
• History of lumbar spine surgery.
• Structural spinal anomalies such as sacralization or lumbarization.
• Spinal deformities, including scoliosis.
• Rheumatologic diseases affecting the spine (e.g., axial spondyloarthritis).
• Significant radiculopathy or advanced neurological deficits, and the presence of extruded or sequestrated lumbar disc herniation.
• Clinically significant lumbar spinal stenosis.
• Spondylolysis and/or spondylolisthesis.
• Acute vertebral fracture, compression fracture, or recent fracture associated with severe osteoporosis.
• Hip or pelvic conditions that may directly influence the Trendelenburg sign, including: History of hip arthroplasty or hip surgery, advanced hip osteoarthritis, residual deformity following lower-extremity fracture, significant leg length discrepancy (>2 cm).
• Systemic or neuromuscular disorders, including multiple sclerosis, myopathies, amyotrophic lateral sclerosis (ALS), stroke, or peripheral neuropathies.
• Pregnancy.
• Severe knee or ankle pathology or other conditions causing substantial gait impairment.

Adults aged 18-65 years with low back pain and available lumbar MRI scans obtained within the previous 12 months. Participants will undergo clinical assessment for Trendelenburg sign and hip function, and lumbar MRI evaluation for degenerative changes.

Individual participant data will not be shared to protect participant confidentiality and in accordance with institutional regulations.