CHAPTER 4

Illium Sacrum Pubic bone Coccyx Obturator foramen Ischial tuberosity Figure 4.2a Sacroiliac joint separated the joint surfaces of the two ilium bones, one on each side (see Figures 4.1, 4.2a and 4.2b). These joints are oriented obliquely (not straight either from side to side or front to back). The surface of the joint is irregular, and the two bones fit together like three-dimensional moonscape puzzle pieces, with hills and valleys nestled together. The iliofemoral joint The iliofemoral joint (hip joint) is a ball- and-socket joint formed by the acetabulum (the socket) and the head of the femur bone (the ball). The acetabulum (Latin for “little vinegar cup”) is located at the front and side of the pelvis. The socket itself is formed by one-third ilium, one-third ischi- um and one-third pubis. For stability and joint health, it is ideal to have the femur head fully and evenly placed in the acetabulum. If it is constant- ly pushed to one side or constantly turned forward or back, it can unevenly wear out the cartilage that lines the inside of the hip joint. For this reason, doing a complete variety of movements for this joint is essential to maintain its health. In other words, we need to do flexion, extension, abduction, adduc- tion, external rotation and internal rotation. The alignment principles of yoga (see below) help us to position the femur in the cen- ter of the acetabulum as much as possible. When we turn the legs in, then move the femurs back and widen them, this complex but essential action places the femoral head back and out to the side in the hip socket. We balance that action with its opposite, drawing in from the sides of the hips and rotating the legs externally for stability. These opposite actions (performed together) will balance the femur in the acetabulum. We’ll see later in this chapter which muscles perform each of those actions. PSIS

Sacroiliac joint

Sacrum Coccyx

Upper pubic ramus Pubic symphysis

Figure 4.2b Sacroiliac joint cross section (superior view)

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