CHAPTER 11 Structure and Function of the Hip Complex


joint capsule and ligaments under a slight amount of tension. Because the gravitational line of force typically falls posterior to the hip joint axis, the hip structures are able to support the body weight passively with minimal activation of hip musculature.


There are numerous bursae at the hip joint associated with the multiple musculotendinous junctions that are subject to large forces. There are three main bursae in the area: over the large bony greater trochanter, between the joint capsule and the iliopsoas tendon, and in the iliopectineal region.


KINEMATICS


The hip joint moves and functions in both open chain non–weight-bearing and closed chain weight-bearing activities as, for example, we swing our legs over the side of the bed before moving into a sitting and then standing position. One hip functions to support the body weight and balance the trunk during closed chain stance, while the opposite hip fl exes and moves in an open chain motion as we take a step when walking to advance the limb. During hip motion, the pelvis can move on a sta- tionary femur, or the femur can move on a fi xed pelvis. During functional tasks, hip muscles contract isometri- cally, eccentrically, and concentrically. Because the pelvis is linked to the spine, movement of the pelvis during closed chain hip motion changes the position of the trunk and spine.


OSTEOKINEMATICS


Osteokinematic motion at the hip occurs when the pelvis is fi xed and the femur moves, or when the concave pelvis moves on the stationary convex femur. In both situations, the motions that occur at the hip are fl exion and exten- sion in the sagittal plane, abduction and adduction in the frontal plane, and medial and lateral rotation in the horizontal plane.


Femur on Pelvis


In the anatomical position, with the hip in neutral or at 0°, the femur rotates anteriorly and has average passive ranges of 120° during fl exion when the knee is fl exed. If the knee is in full extension and the hip is passively fl exed, the hamstring muscles are stretched over a fl exed hip and extended knee, becoming passively insuffi cient. In this position, the hamstrings can limit the amount of hip fl exion available, depending on the person’s muscle fl exibility (Fig. 11.13). When moving from fl exion back to neutral, the femur moves posteriorly and extends. Neutral is again the 0° mark, and as the femur moves posteriorly beyond zero, it typically displays approxi- mately 20° of passive hip extension if the knee is extended. If the knee is fl exed during hip extension past neutral, the anterior rectus femoris muscle is stretched over an extended hip and fl exed knee and can limit the available amount of hip extension range of motion (Fig. 11.14). Hip fl exion and extension occur in the sagittal plane around a frontal axis.


237


A


B


C


Figure 11.13 Side view of hip flexion. (A) Hips in neutral. (B) Right hip flexion with knee extension. (C) Right hip flexion with knee flexion.


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