How does a shoulder dislocation occur?
As briefly described above, there are various causes for the occurrence of shoulder dislocation. Most frequently, however, a levering movement of the upper arm with simultaneous external rotation can be seen in which the arm moves away from the body. The head of the humerus usually jumps forward (axillary luxation) or downward (subcoracoidal luxation) in a shoulder dislocation.
Dislocations to the back are rather untypical. Only very rarely does a shoulder luxate with an arm stretched upwards. As a rule, shoulder dislocations have traumatic causes: falls, sports, bicycle or other traffic accidents should be mentioned in this context. The more rarely occurring habitual shoulder dislocations (see above) lead to dislocation without adequate trauma (minor trauma) due to individual events (e.g. congenital glenoid dysplasia).
Diagnosis of a shoulder joint dislocation
The diagnosis of shoulder dislocation is primarily a clinical examination. However, depending on the severity of the dislocation, this may be difficult under certain circumstances. In particular in the case of distortions (twisting) and subluxations (incomplete dislocation), the patient’s medical history is therefore very important in differentiating between the various forms of dislocation.
During the clinical examination, the doctor palpates the shoulder and, in the case of dislocation, can feel the empty socket, the protruding bony acromion and the dislocated head of the humerus. If an attempt is made to carefully reposition the dislocated arm, it jumps back into the wrong position, which is known as “spring fixation”. The examination should also cover possible concomitant injuries such as damage to a nerve.Necessary instrumental examinations Instrumental examinations useful in individual cases
- X-ray of the shoulder in 2 planes to define the type and to determine any accompanying bony injuries.
X-rays can also be used to determine the cause of dislocation (e.g. dysplasia, etc. ).
- Sonography (especially to exclude a rotator cuff lesion)
- Special X-ray images, e.g. : Velpeau image (positional relationship between humeral head and socket), ventrodorsal 60° internal rotation image (Hill-Sachs view), socket profile image
- MRI of the shoulder joint
- CT (if necessary air-arthro-CT)
The diagnosis by means of an MRI is of central importance for many injuries. The importance is based on the fact that the extent of the injury can best be determined with an MRI, since an MRI image shows joints and soft tissues very well.
As a result, treatment planning can be optimally determined. An MRI can reveal bony injuries, such as a notch in the back surface of the head of the humerus. A special eye mark is located on the joint lip.
This is a ring of ligaments that lies around the joint socket. The MRI clearly shows a detachment of this joint lip. An important criterion is also the assessment of the condition of the biceps tendon and the nerves running there.
