Introduction
Internal rotation is the rotational movement of a limb around its longitudinal axis. The direction of rotation points inwards. The outer side of the limb is turned towards the body (medially).
In order to perform an internal rotation, the joint must be a ball joint or a swivel/hinge joint. Ball joints are for example the shoulder or hip joint. Swivel-hinge joints are for example the knee joint or the Ellen-Speichen joint.
Internal rotation in the hip
The hip joint is a nut joint and thus belongs to the group of ball joints. As a ball-and-socket joint, it can be moved in all directions. The hip joint consists of a small femoral head, which is formed by the femur, and a large socket, which is formed by the acetabulum.
The acetabulum completely encloses the femoral head, so that dislocation of the joint is rather rare. In addition, the hip joint is stabilized by numerous fixed ligaments and muscles. The degrees of freedom – an indication of how many degrees a joint can be moved – are for the hip joint: flexion up to approx.
140°, extension up to approx. 20°, abduction up to approx. 50° when the hip joint is extended, adduction up to approx.
30° when the hip joint is extended, internal rotation by approx. 40°, external rotation by approx. 50°, when the hip joint is flexed. The most important muscles that cause internal rotation in the hip joint are the gluteal muscles (Musculus gluteus medius and Musculus gluteus minimus), the femoral ligament tensioner (Musculus tensor fasciae latae), and the large adductor muscle (Musculus adductor magnus). Painful internal rotation in the hip joint is a particular indication of hip joint arthrosis.
Internal rotation in the shoulder
Like the hip joint, the shoulder joint (glenohumeral joint) is a ball and socket joint. However, the glenohumeral joint consists of a relatively large joint head, which is formed by the humerus, and a relatively small, flat socket, which is formed by the shoulder blade. Furthermore, the shoulder joint is largely stabilized only by the rotator cuff, so that it can luxate very quickly in case of accidents.
On the other hand, the shoulder joint also has a very high degree of mobility, which is indispensable for the arm. The other subjoints of the shoulder girdle – the acromioclavicular joint and the sternoclavicular joint – also play an important role in the mobility of the shoulder joint. Depending on the movement to be performed, the position of the clavicle and the shoulder blade is adjusted to the movement.
The most important muscle for internal rotation in the shoulder joint is the subscapular muscle. The degrees of freedom of the shoulder joint for the anteversion (movement of the arm forward) are 90°. Raising the arm more than 90° to 170° (elevation) is only possible with the involvement of the shoulder girdle.
A retroversion (movement of the arm backwards) is possible up to 40°. A sole abduction in the shoulder joint is possible up to 90°, with participation of the shoulder girdle up to 180°. Adduction is possible up to 20-40°.
The degree of freedom for internal rotation of the shoulder joint is 95°, for external rotation 40-60°. The internal rotation in the shoulder joint can be checked using the apron handle. With the apron handle, the patient is asked to cross his hands behind his back. Painful internal rotation in the shoulder joint often indicates damage or rupture of the rotator cuff, especially of the subscapular muscle.
