Like all other joints, the muscles help provide support in addition to creating motion. If the muscles of the hip and tight/weak it can cause issues to arise at the ankle, knee, back as well as at the hip.

Muscles of greater significance are:

Tensor Fascia Latae
This muscle runs from the flare of the hip bone (ilium) all the way down to the knee. Tightness of this muscle can cause increased pressure and friction over the hip itself (greater trochanter) and the underlying bursa resulting in hip pain (tendonitis or bursitis). It can also lead to pain in the knee and or outer thigh.

Rectus Femoris
This is one of the quadricep muscles that runs from the knee to the top of the pelvis. This muscle is highly used (trained by runners and kickers) for it helps extend the knee and flex the hip. Tightness and/or weakness in this muscle can lead to back, hip or knee pain.