This is what happens……when you’re walking…let’s use the right leg, I’ll describe what you’ll see with the right leg. When you’re walking and it’s time for the right leg to leave the ground and advance forward, you need muscles to kick in so that your right foot can clear the ground. A lot of times after a stroke your leg will have trouble clearing the ground because of weak shin muscles leading to foot drop, meaning you must strengthen your tibialis anterior muscle.
In this case, it’s weak hip muscles. Stand on both feet, now lift up your right leg, do your hips stay level and unmoving or when you lifted your right leg off the ground did your right hip drop? The correct answer is that your hips stayed level.
When you lift up your right leg, the hip abductor muscles on the OPPOSITE side of the body turn on to prevent your hip from dropping. Since your left leg is stationary, the only way to ABDUCT(move away from the body) the left leg is to raise the right hip. If the hip abductor muscles on the left side are weak, the right hip will drop when the right leg is lifted off of the ground. So if you see a hip drop on the right side, it means that the left hip muscles are weak.
This drop of the hip is called the Trendelenburg sign. Sometimes, the body has compensated in order to find a way to clear the foot when walking. This compensation is by the upper body leaning to the left(in the case of right hip drop) in order to pull the right leg up and allow the foot to clear the ground. So the body will lean to the affected side during advancement of the opposite leg. If you’re affected on the left, the upper body will lean to the left when advancing your right foot forward during the gait cycle. If you’re right side affected, the upper body will lean to the right when advancing the left leg forward. So if this happens to you, you’ll want to exhaustively strengthen the hip abductor muscles.