Hip mechanics (Core center of motion) and the knee

The hip joint is a ball and socket joint ( I.e. it then is able to move on any axis it wishes, like the shoulder), formed at the hip bone, and hip socket. The femoral head, which is the only movable part of the hip joint, is designed to glide and rotate within the socket as the hip moves.The femoral head is round and is designed to fit snugly inside the acetabulum. A thick, fibrous sheath of connective tissue called the hip joint capsule surrounds the hip joint and increases its stability. When the hip moves, the hip joint capsule helps to ensure a tight, snug fit of the femoral head inside the acetabulum.

So... these are all the moves that the hips control.

 

Movement of the hip joint is made possible by a series of powerful muscles that act upon the hip joint and provide the force necessary to move the hip joint through its full range of motion. Thick bands of fibrous tissue, otherwise known as ligaments, connect various muscles to the hip joint.  When hip muscle actions exert force against the hip joint, the femoral head rotates to various degrees inside the acetabulum.

 

 

 

 

 However the knee is a clever (door) hinge as it actually doesn't actually rotate so much on it's own as with the hip, the only two actions it provides (flexion) bringing the foot closer to the body or (extension) away from the body. Designed to lock the leg in place when bringing weight on it (I.e. walking, shifting side to side etc.)

 

 
Websites:

http://www.conceptart.org/forums/showthread.php?p=1883011
http://www.ehow.com/how-does_5167231_hip-joint-work.html
 http://nursing411.org/Courses/MD0556_Basic_Patient_Care_Procedures/2-06_Basic_Pat_Care_Proc.html