A rotation always refers to a rotational movement of a body part. This takes place around a so-called rotation centre, which is formed by the centre of the joint. In the case of an external rotation, the rotational movement is performed from the front to the outside.
This is in contrast to internal rotation, where the rotational movement is directed inwards. An external rotation can be performed by the joints of the extremities. This is possible in the shoulder joint, hip joint and foot joint.
A so-called rotational movement of hands and feet does not exist in this sense. It corresponds to the movement known as pronation or supination. In order to enable an external rotation or an internal rotation, the joint must be a ball or wheel joint.
External rotation in the hip
The hip joint is a ball joint and can therefore be moved in almost all directions. The external rotation of the hip consists of a rotational movement of the femoral head in the acetabulum outwards. This can be carried out, for example, when the knee is pulled towards the chest in the supine position and turned outwards.
Normally, the external rotation is about 50° when the hip joint is bent at 90°, but only 30° when the hip is extended (i.e. with the leg stretched out). Many different muscles are responsible for the external rotation. These include the short and the long thigh extensor (Musculi adductores longus et brevis), the gluteal muscles (Musculi glutei), and other smaller muscles or muscle groups.
The rotational movement of the hip is of great importance when walking. Here there is an interplay of movements of the hip, knee and foot joints. If one of these joints is not fully mobile, the other joints have to compensate for this loss of function and damage can occur due to the incorrect load.
External rotation in the shoulder
An external rotation of the shoulder consists of an outward rotation of the humeral head in the socket. The outer part of the upper arm is thus rotated backwards. The interaction of different muscles makes this movement possible.
As a rule, however, the shoulder joint performs combined movements consisting of rotations and movements about other axes. The external rotation is normally about 60°. Both shoulder and back muscles are involved in the movement. In particular, the so-called supraspinatus and infraspinatus muscles, as well as the deltoid muscle, take on this task.
External rotation in the knee
The knee joint cannot be turned inwards or outwards when in the extended position. This is because the collateral ligaments of the joint are very tight and prevent this. When the knee is bent (flexed), however, the collateral ligaments are slack and allow rotational movements of the knee joint.
External rotation is possible up to about 30° with a flexed knee and is less inhibited by the cruciate ligaments than internal rotation. During external rotation, the foot rotates outwards. The menisci also move with it. The only muscle that can trigger an external rotation in the knee joint is the so-called muscle biceps femoris.