Плечевой сустав: анатомия и функции

the part of the human body
Part of the body

The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The shoulder joint, also known as the glenohumeral joint, is the major joint of the shoulder, but can more broadly include the acromioclavicular joint. In human anatomy, the shoulder joint comprises the part of the body where the humerus attaches to the scapula, and the head sits in the glenoid cavity. The shoulder is the group of structures in the region of the joint. The shoulder joint is the main joint of the shoulder. It is a ball and socket joint that allows the arm to rotate in a circular fashion or to hinge out and up away from the body. The joint capsule is a soft tissue envelope that encircles the glenohumeral joint and attaches to the scapula, humerus, and head of the biceps. It is lined by a thin, smooth synovial membrane. The rotator cuff is a group of four muscles that surround the shoulder joint and contribute to the shoulder's stability. The muscles of the rotator cuff are supraspinatus, subscapularis, infraspinatus, and teres minor. The cuff adheres to the glenohumeral capsule and attaches to the humeral head. The shoulder must be mobile enough for the wide range actions of the arms and hands, but stable enough to allow for actions such as lifting, pushing, and pulling.

The shoulder consists of a ball and socket joint formed by the humerus and scapula and their surrounding structures ligaments, muscles, tendons which support the bones and maintain the relationship of one to another. White hyaline cartilage on the ends of the bones (called articular cartilage) allows the bones to glide and move on each other, and the joint space is surrounded by a synovial membrane. Around the joint space are muscles the rotator cuff, which directly surrounds and attaches to the shoulder joint and other muscles that help provide stability and facilitate movement. Two filmy sac like structures called bursae permit smooth gliding between bone, muscle, and tendon. They cushion and protect the rotator cuff from the bony arch of the acromion. The glenoid labrum is the second kind of cartilage in the shoulder which is distinctly different from the articular cartilage. This cartilage is more fibrous or rigid than the cartilage on the ends of the ball and socket. Also, this cartilage is also found only around the socket where it is attached.

Under the influence of testosterone and growth hormone, the shoulders broaden in males during puberty.

The shoulder is the most mobile and potentially unstable joint in the body. Due to this, it is often prone to problems.

Fractures of shoulder bones can include clavicular fractures, scapular fractures, and fractures of the upper humerus.

Shoulder problems, including pain, are common and can relate to any of the structures within the shoulder. The primary cause of shoulder pain is a rotator cuff tear. When this type of cartilage starts to wear out (a process called arthritis), the joint becomes painful and stiff. The conventional invasive arthrography is nowadays being replaced by the non invasive MRI and ultrasound, and is used as an imaging reserve for patients who are contraindicated for MRI, for example pacemaker carriers with an unclear and unsure ultrasonography.

There are several advantages of ultrasound. It is relatively cheap, does not emit any radiation, is accessible, is capable of visualizing tissue function in real time, and allows the performance of provocative maneuvers in order to replicate the patient’s pain. Those benefits have helped ultrasound become a common initial choice for assessing tendons and soft tissues. Limitations include, for example, the high degree of operator dependence and the inability to define pathologies in bones. One also has to have an extensive anatomical knowledge of the examined region and keep an open mind to normal variations and artifacts created during the scan. Although musculoskeletal ultrasound training, like medical training in general, is a lifelong process, Kissin et al. suggests that rheumatologists who taught themselves how to manipulate ultrasound can use it just as well as international musculo skeletal ultrasound experts to diagnose common rheumatic conditions. After the introduction of high frequency transducers in the mid 1980s, ultrasound has become a conventional tool for taking accurate and precise images of the shoulder to support diagnosis. Adequate for the examination are high resolution, high frequency transducers with a transmission frequency of 5, 7.5, and 10 MHz. To improve the focus on structures close to the skin an additional "water start up length" is advisable. During the examination the patient is asked to be seated, the affected arm is then adducted and the elbow is bent to 90 degrees. Slow and cautious passive lateral and/or medial rotations have the effect of being able to visualize different sections of the shoulder. In order to also demonstrate those parts which are hidden under the acromion in the neutral position, a maximum medial rotation with hyperextension behind the back is required. To avoid the different tendon echogenicities caused by different instrument settings, Middleton compared the tendon’s echogenicity with that of the deltoid muscle, which is still lege artis. Usually the echogenicity compared to the deltoid muscle is homogeneous intensified without dorsal echo extinction. Variability with reduced or intensified echo has also been found in healthy tendons. Bilateral comparison is very helpful when distinguishing and setting boundaries between physiological variants and a possible pathological finding. Degenerative changes at the rotator cuff often are found on both sides of the body. Consequently, unilateral differences rather point to a pathological source and bilateral changes rather to a physiological variation. To accurately evaluate the echogenicity of an ultrasound, one has to take into account the physical laws of reflection, absorption and dispersion. It is at all times important to acknowledge that the structures in the joint of the shoulder are not aligned in the transversal, coronal or sagittal plane, and that therefore during imaging of the shoulder the transducer head has to be held perpendicularly or parallel to the structures of interest. Otherwise the appearing echogenicity may not be evaluated.

Orthopedics established the MRI early on as the tool of choice for joint and soft tissue imaging because of its non invasiveness, lack of radiation exposure, multi planar slicing possibilities and the high soft tissue contrast. MRIs can provide joint details to the treating orthopedist, helping them to diagnose and decide the next appropriate therapeutic step. To examine the shoulder, the patient should lay down with the concerned arm is in lateral rotation. For signal detection it is recommended to use a surface coil. To find pathologies of the rotator cuff in the basic diagnostic investigation, T2 weighted sequences with fat suppression or STIR sequences have proven value. In general, the examination should occur in the following three main planes: axial, oblique coronal and sagittal. Most morphological changes and injuries are sustained to the supraspinatus tendon. Traumatic rotator cuff changes are often located antero superior, meanwhile degenerative changes more likely are supero posterior. Tendons are predominantly composed of dense collagen fiber bundles. Because of their extreme short T2 relaxation time they appear typically signal weak, respectively, dark. Degenerative changes, inflammations and also partial and complete tears cause loss of the original tendon structure. Fatty deposits, mucous degeneration and hemorrhages lead to an increased intratendinal T1 image. Edema formations, inflammatory changes and ruptures increase the signals in a T2 weighted image. In 1999, Weishaupt D. et al. reached through two readers a significant better visibility of pulley lesions at the rotator interval and the expected location of the reflection pulley of the long biceps and subscapularis tendon on parasagittal (reader1/reader2 sensitivity: 86%/100%; specificity: 90%/70%) and axial (reader1/reader2 sensitivity: 86%/93%; specificity: 90%/80%) MRA images. When examining the rotator cuff, the MRA has a couple of advantages compared to the native MRI. Through a fat suppressed T2 weighted spin echo, MRA can reproduce an extreme high fat water contrast, which helps to detect water deposits with better damage diagnosis in structurally changed collagen fiber bundles.

Tetrapod forelimbs are characterised by a high degree of mobility in the shoulder thorax connection. Lacking a solid skeletal connection between the shoulder girdle and the vertebral column, the forelimb's attachment to the trunk is instead mainly controlled by serratus lateralis and levator scapulae. Depending on locomotor style, a bone connects the shoulder girdle to the trunk in some animals; the coracoid bone in reptiles and birds, and the clavicle in primates and bats. In primates, the shoulder shows characteristics that differ from other mammals, including a well developed clavicle, a dorsally shifted scapula with prominent acromion and spine, and a humerus featuring a straight shaft and a spherical head.