In Phelps test, how does the concept work for gracilis being tight? It says that if abduction further with knee in flexion in prone. Then it means it is gracilis tightness. Gracilis is a hip flexor int rot and add. Please, can you explain.

The Phelps test (or Felps test or Phelps-Baker test) is a clinical examination used to determine the degree of contracture of the gracilis muscle. The patient lies prone with the knees extended, the examiner passively abducts both the hips and legs as far as possible. The knees are then flexed to 90 deg and the examiner tries to abduct the hips further. If abduction increases, the test is considered positive for gracilis muscle contracture.

The gracilis muscle adducts, medially rotates, flexes the hip and also aids in flexion of the knee.

To stretch the gracilis, the hips and legs are ABDucted. Flexing the knees (recall that the gracilis is also a knee flexor) shortens the muscle and in the case of an already tight gracilis, causes an ever so slight ADDuction of the hips/legs. It is this slight ADDuction, caused by gracilis tightness, that enables the examiner to achieve further ABDuction with knee flexion and thus documents a positive examination.

To further corroborate this explanation, a variation of this test indicates that if gracilis is shortened, then the hip will automatically ADDuct on passive full extension of the knee.

Reference 1: David J. Magee. Orthopedic Physical Assessment. 6th Edition, 2014. Elsevier Publishers. Chapter 11 (Hip), Pg 726.