Thomas's test (Hugh Owen Thomas)
It is a way of assessing whether the patient has a fixed flexion deformity of the hip – checking whether or not the patient can extend his hip.
Pierre Sterckx sent us this comprehensive description of how it is done (see disclaimer):
Place one hand flat on the examining table under the patient's lumbar lordosis. Have the patient fully flex the hip on the side opposite the one being assessed. This will cause rotation of the pelvis and flattening of the lumbar lordosis (you will feel his back pressing against your hand). See if the leg being assessed, in this case the right one, is slightly elevated off the examining table.
The patient should be lying supine on the examining table. Place your left hand under the patient's lumbar spine so it lies between the patient's back and the examining table. If the patient has a lumbar lordosis, your hand will easily slip between his back and the table. If there is no lumbar lordosis and your hand does not slip in easily, and if the patients legs are both resting flat on the examining table, the patient does not have a fixed flexion deformity, and there is no need to proceed with the rest of the test.
The next step is to have the patient fully flex the normal leg (the leg opposite the one you are testing for a fixed flexion deformity). Have him pull his knee against his chest. This will cause the pelvis to rotate with the symphysis pubis moving upwards towards the head. As the patient reaches the end point of flexion, you will feel his lumbar spine press against your hand as the lumbar lordosis straightens out.
If the patient has a fixed flexion deformity (meaning that the hip can not be fully extended), the leg opposite the one being flexed will rise a few degrees off the examining table because it is being pulled up as the pelvis rotates. Push down on the thigh of the side being assessed to help you check whether or not it has been pulled up off the table. If there is no fixed flexion deformity, the leg opposite that being flexed will simply extend as the pelvis rotates, and it will not rise from the table.
In other words, the Thomas test allows you to assess whether the supine patient has at least some degree of hip extension. If you want to assess the full range of extension, have the patient assume the prone position on the table and then extend the hip.