Which statement best describes the psoas muscle?

Which statement best describes the psoas muscle?

• A. It is a triangular muscle that lies posterior to the kidney and runs along the spine
• B. It is a flat superficial abdominal muscle
• C. It is the largest back muscle
• D. It originates from the rib cage

Answer: (A)

The psoas major is a deep, longitudinal muscle of the posterior abdominal wall that originates from the lower thoracic and upper lumbar vertebrae and descends along the lumbar spine to the femur. It lies retroperitoneally, adjacent to the spine and just posterior to the kidney, forming part of the posterior abdominal wall. Describing it as a triangular muscle that lies behind the kidney and runs along the spine matches its location and orientation seen in imaging and anatomy, making this the best description. It is not a flat superficial abdominal muscle, it is not the largest back muscle, and it does not originate from the rib cage; its origins are from the vertebral bodies and discs of T12–L5.

The psoas major is a deep, longitudinal muscle of the posterior abdominal wall that originates from the lower thoracic and upper lumbar vertebrae and descends along the lumbar spine to the femur. It lies retroperitoneally, adjacent to the spine and just posterior to the kidney, forming part of the posterior abdominal wall. Describing it as a triangular muscle that lies behind the kidney and runs along the spine matches its location and orientation seen in imaging and anatomy, making this the best description. It is not a flat superficial abdominal muscle, it is not the largest back muscle, and it does not originate from the rib cage; its origins are from the vertebral bodies and discs of T12–L5.