In the Thomas test, external rotation of the extended leg is indicative of which tightness?

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The main concept is that the Thomas test helps assess hip flexor length, especially the iliopsoas, by observing how the leg behaves when the opposite knee is brought toward the chest. If the leg that stays extended rotates outward (external rotation), this pattern specifically suggests tightness of the iliotibial band via the tensor fascia latae. The IT band and TFL pull on the lateral hip and knee, and when the hip tries to extend while the leg is held straight, that tight lateral structure causes the leg to rotate externally.

In contrast, tight iliopsoas would mainly keep the hip flexed and prevent full extension of the hip, not produce external rotation of the extended leg. Quadriceps tightness affects knee motion rather than causing this distinctive external rotation, and a sprain of the LCL is a knee ligament issue not what this test is designed to indicate. So external rotation of the extended leg points to iliotibial band tightness.