Page 43 - ASOP ROT Study Guide

3 . 1 Stability
Three factors contribute to hip joint stability:
♦ Shape,
♦ Ligaments, and
♦ Muscles.
The shape of the joint makes it stable. A ball and socket construction is the best configuration for
both stability and variety of directions movement.
Ligaments are also important for the stability of the hip joint but are secondary to the shape. The
ligaments are particularly strong around the anterior and inferior sides of the joint (illustrated
below). This means that the head of the femur is most likely to dislocate by being forced backwards
out of the acetabulum. Even to do this requires a lot of force and traumatic hip dislocation is rarely
seen except after serious road traffic accidents.

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Finally the joint is covered in a thick layer of muscles which will be described in detail later.
Although the primary function of these muscles is to cause movement of the lower limb, they make
an important contribution to the stability of the hip.
The result of these factors is a joint that is very stable over a wide range of angular movement.
This is an essential requirement because of the large propulsive forces that the muscles in that area
impart to the body.

3 . 2 Type of Movement
When we describe hip joint motion in terms of planes the following names are used:
♦ Flexion - rotation of the femur so it swings forwards in the sagittal plane
♦ Extension - rotation of the femur so it swings backwards in the sagittal plane
♦ Abduction - rotation of the femur so it swings laterally in the coronal plane
♦ Adduction - rotation of the femur so it swings medially in the coronal plane