During the Thomas test, abduction or external rotation of the extended leg indicates tightness of which muscle?

During the Thomas test, abduction or external rotation of the extended leg indicates tightness of which muscle?

• A. Iliopsoas.
• B. Hamstrings.
• C. Rectus femoris.
• D. Gluteus maximus.

Answer: (C)

The Thomas test is used to assess the length of the hip flexors, particularly the rectus femoris, which crosses both the hip and knee. When you bring the thigh up toward the chest to flatten the lumbar spine, a normally lengthened hip flexor allows the knee to flex as the thigh drops toward the table. If the knee of the tested leg stays extended (the leg remains straight) and the limb abduces or externally rotates, this pattern points to tightness of the rectus femoris. Rectus femoris being a biarticular muscle that crosses both joints means it can restrict knee flexion while the hip is flexed, leading to that extended knee and compensatory outward movement. The other muscles would produce different signs: iliopsoas tightness more clearly limits hip extension patterns with less specific abduction/external rotation of an extended leg, hamstring tightness shows up as limited knee extension in other tests, and gluteus maximus tightness affects rotation and extension patterns in ways not described by this sign.

The Thomas test is used to assess the length of the hip flexors, particularly the rectus femoris, which crosses both the hip and knee. When you bring the thigh up toward the chest to flatten the lumbar spine, a normally lengthened hip flexor allows the knee to flex as the thigh drops toward the table. If the knee of the tested leg stays extended (the leg remains straight) and the limb abduces or externally rotates, this pattern points to tightness of the rectus femoris. Rectus femoris being a biarticular muscle that crosses both joints means it can restrict knee flexion while the hip is flexed, leading to that extended knee and compensatory outward movement. The other muscles would produce different signs: iliopsoas tightness more clearly limits hip extension patterns with less specific abduction/external rotation of an extended leg, hamstring tightness shows up as limited knee extension in other tests, and gluteus maximus tightness affects rotation and extension patterns in ways not described by this sign.