Page 44 - ASOP ROT Study Guide

♦ Internal rotation - rotation of the femur about its long axis resulting in the knee cap pointing
inwards

♦ External rotation - rotation of the femur about its long axis resulting in the knee cap pointing
outwards

♦ Circumduction - movement of the distal femur in a circle without internal or external rotation
taking place. In a large circumduction the hip moves through the following positions: flexed -
abducted - extended - adducted.

Internal External
Rotation Rotation

http://nritarutya.com/know-hip/

The actual angular ranges of these different motions are not important to remember at this stage.
However, as an aid to diagnosis, if one hip has a smaller range of movement than the other
then there is likely to be something significantly wrong with one of the joints.

3 . 3 Classification of Muscle Action

The movements described above are achieved by the muscles crossing the joint. Such muscles
can be regarded as the "motors" of the joint. Many of these muscles act to produce a movement
that does not lie exactly in one of the anatomical planes. For example one muscle may
simultaneously flex and abduct resulting in motion in a plane somewhere between the sagittal and
coronal planes (i.e. the motion takes place in both planes).

Most muscles act more powerfully in one anatomical plane and less powerfully in the others. In
the plane where the muscle is less powerful, motion is generated with assistance from other
muscles. The most powerful muscle contributing to a movement in a particular direction is known
as the prime mover. For any other directions it will be a secondary mover. For example the psoas
is the prime flexor of the hip and the quadriceps is a secondary hip flexor and the prime extensor of
the knee.

Remember that if a muscle crosses two joints, it will tend to cause motion of both joints. For
example, the hamstrings cross the hip and the knee. If they contract alone they will extend the hip
and flex the knee. In practice other muscles may contract to prevent the knee flexing as the
hamstrings contract to extend the hip. When muscles act against each other in this way to prevent a
movement they are called antagonists. One the other hand when muscles act alone or in
combination to produce a movement they are called agonists.