MRT for a torn tendon
Whenever there is a strong suspicion of a torn tendon in the shoulder (torn or torn rotator cuff) and the medical history and physical examination of the shoulder joint indicate this, special imaging is necessary to confirm or substantiate the suspicion and subsequently initiate optimal therapy. The imaging methods used include ultrasound and, in particular, MRI imaging of the shoulder joint. The latter is particularly good because magnetic resonance imaging produces high-resolution sectional images and is particularly suitable for imaging non-bony tissue (including tendons). Often a contrast medium is necessary during or before the MRI examination to improve imaging and to obtain even more precise images of the shoulder joint and surrounding structures. On an MRI image, the treating physician can then see exactly whether, where and to what extent a tendon has torn, so that a decision can then be made as to whether conservative or surgical therapy is appropriate and must be initiated.
Anatomy of the shoulder joint
- Definition and structureThe shoulder joint consists of several parts that articulate (interact) with each other. One is the spherical head of humerus (caput humeri), which, together with the oval joint surface (cavitas glenoidalis) of the shoulder blade (scapula), forms the most mobile ball and socket joint in the human body. This ball joint is so mobile because there is hardly any bony guidance.
Since the joint surface of the shoulder blade, due to its oval shape and size, does not fit perfectly with the head of humerus, the joint surface must be enlarged. For this reason, the cavitas glenoidalis is surrounded by a 3-4 mm wide glenoid labrum (Labrum glenoidale).
- The glenoid lip consists of fibrous cartilage and is attached to the articular surface of the shoulder blade. Furthermore, the joint capsule of the shoulder joint is very slack.
This looseness and slackness causes an approx. 1 cm long reserve zone (axillary recessus) to develop towards the bottom (caudally). However, the recessus is only visible when the joint is in a relaxed position.
- Ligamentous apparatusThe ligamentous apparatus of the shoulder joint is very weakly developed, although the stress is very high compared to the other joints.
There is therefore no guidance through the ligaments. The joint is mainly held in place by the strongly developed musculature. Due to the ligaments’ slackness, luxations (dislocations), as well as muscle and tendon tears, very often occur due to the strong stress on them.
The following ligaments (the ligament is called ligamentum in Latin, it is abbreviated to ligamentum) are associated with the shoulder joint: Reinforcing ligament of the shoulder joint capsule (Lig. coracohumerale). This ligament runs from the processus coracoideus (bony process of the shoulder blade = scapula) to the humerus.
It is of great importance for the stabilization of the shoulder joint. The ligament consists of two different parts, with one part extending from the humerus to the shoulder blade and the other part from the humerus to another ligament, the acromioclavicular ligament (Lig. coracoaacromiale).
This ligament is not part of the ligamentous apparatus of the shoulder joint, but covers the head of the humerus. The second ligament, which belongs to the shoulder joint, runs from the glenoid labrum at the joint capsule (Labrum glenoidale) (Lig. coracoglenoidale) to the bony process of the scapula (processus coracoideus).
The third are the Ligg. glenohumeralia. These are several ligaments that run from the edge of the socket of the joint capsule to the head of the humerus.
- Muscles All the muscles that support the shoulder joint and make the movements possible lie around the joint like a cuff.
Therefore, when all muscles are combined, we speak of the rotator cuff.It was composed of four different muscles: The lower bone muscle (musculus infraspinatus), upper bone muscle (musculus supraspinatus), lower shoulder leaf muscle (musculus subscapularis), and the small round muscle (musculus teres minor). Together with the reinforcing ligament of the articular capsule of the shoulder joint (lig. coracohumerale), they form a tough tendon cap that surrounds the joint like a cuff.
They extend roughly from the shoulder blade (scapula) to the humerus. The most important task of this musculature is, as mentioned at the beginning, the stabilization of the shoulder joint. They press the humerus into the glenoid cavity.
They are also very important for various movements: internal rotation (only for ball or wheel joints. Here, the outer side of the arm is turned towards the center of the body), external rotation (the side of the upper arm facing the body is turned away from the body) and abduction (the lateral spreading of a body part away from the center of the body).
- Bursa sacs The bursa sacs are very important for the correct function of the shoulder joint. The bursa subtendinea musculus subscapularis lies under the tendon of the lower shoulder blade muscle and ensures that there is no friction between the tendon and the shoulder blade (scapula).
There is an oval cavity through which the bursa can communicate with the joint capsule. Under the bony projection of the shoulder blade (Processus coracoideus) there is also a bursa, the bursa subcoracoidea. It has the function of a reserve space for the joint.
The bursa under another bony projection of the shoulder blade, the acromion (bursa subacromialis) and the bursa under the deltoid muscle (bursa subdeltoidea) together form the subacromial collateral joint. From an anatomical point of view, it is not a real joint, but it supports the abduction of the arm.
- Importance of hydrogen in structures for MRI The human organism consists of about 70% water. Hydrogen is the predominant element of the body.
The positively charged water molecules can be magnetized, which makes the MRI of the shoulder useful. The bone appears black or white on the MRI image, depending on its weighting (T1, T2, PD), because it is particularly low in hydrogen, while the soft tissues are very rich in hydrogen. In the MRI of the shoulder joint, only the different proportion of hydrogen atoms is actually detected and the differences produce the contrast and thus the MRI image.
Depending on their hydrogen content, soft tissues can be distinguished very well from one another in MRI. They are then displayed in different shades of grey. In most cases, malignant and benign tissue can also be distinguished from each other.
