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The hip joint, or coxofemoral joint, is the articulation of the acetabulum of the pelvis and the head of the femur (Fig. 10–1). These two segments form a diarthrodial ball-and-socket joint with three degrees of freedom: flexion/extension in the sagittal plane, abduction/adduction in the frontal plane, and medial/lateral rotation in the transverse plane. Although the hip joint and the shoulder complex have a number of common features, the functional and structural adaptations of each to its respective roles have been so extensive that such comparisons are more of general interest than of functional relevance. The role of the shoulder complex is to provide a stable base on which a wide range of mobility for the hand can be superimposed. Shoulder complex structure gives precedence to open-chain function. The primary function of the hip joint is to support the weight of the head, arms, and trunk (HAT) both in static erect posture and in dynamic postures such as ambulation, running, and stair climbing. The hip joint, like the other joints of the lower extremity that we will examine, is structured primarily to serve its weight-bearing functions. Although we examine hip joint structure and function as if the joint were designed to move the foot through space in an open chain, hip joint structure is more influenced by the demands placed on the joint when the limb is bearing weight. As we shall see later in this chapter, weight-bearing function of the hip joint and its related weight-bearing responses are basic to understanding the hip joint and the interactions that occur between the hip joint and the other joints of the spine and lower extremities.

Figure 10–1

The hip joint is formed by the head of the femur and the acetabulum of the innominate bone (one half) of the pelvis.

Case 10-1: Patient Case

Gabriella Martinez is a 32-year-old woman currently teaching kindergarten, a position she has held for the past 10 years. Gabriella has been bothered with recurrent left hip pain that has been intermittent throughout her young adult life. She recalls several instances of hip pain that interrupted her participation in gymnastics and dance as a teenager. Although Gabriella no longer participates in dance or gymnastics, she remained physically active until recently by running as well as taking Pilates and yoga classes.

Over the past few months, though, she has experienced increasing problems, predominantly on her left side, that interfere with climbing the stairs in her two-story home, performing activities with her kindergarten class, and caring for her 3-year-old daughter. In addition to pain complaints, she also reports feeling as though her hip may "pop out of the socket" when she is doing twisting poses in yoga and Pilates and has an occasional painful "click" in the hip. Therefore, it has become too painful for her to run and she has suspended ...

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