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 . 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.
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.
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. This capsule is strengthened by the coracohumeral ligament which attaches the coracoid process of the scapula to the greater tubercle of the humerus. There are also three other ligaments attaching the lesser tubercle of the humerus to lateral scapula and are collectively called the glenohumeral ligaments.
The transverse humeral ligament, which passes from the lesser tubercle to the greater tubercle of humerus, covers the intertubercular groove, in which the long head of biceps brachii travels.
The four of these muscles converge to form the rotator cuff tendon. This tendon, along with the articular capsule, the coracohumeral ligament, and the glenohumeral ligament complex, blend into a confluent sheet before insertion into the humeral tuberosities. The infraspinatus and teres minor fuse near their musculotendinous junctions, while the supraspinatus and subscapularis tendons join as a sheath that surrounds the biceps tendon at the entrance of the bicipital groove.
In addition to the four muscles of the rotator cuff, the deltoid muscle and teres major muscles arise and exist in the shoulder region itself. The deltoid muscle covers the shoulder joint on three sides, arising from the front upper third of the clavicle, the acromion, and the spine of the scapula, and travelling to insert on the deltoid tubercle of the humerus. Contraction of each part of the deltoid assists in different movements of the shoulder - flexion (clavicular part), abduction (middle part) and extension (scapular part). The teres major attaches to the outer part of the back of the scapula, beneath the teres minor, and attaches to the upper part of the humerus. It helps with medial rotation of the humerus.
Muscles from the front
Muscles from the chest wall that contribute to the shoulder are:
Function |
It fixes the scapula into the thoracic wall and aids in rotation and abduction of the shoulders. |
It depresses the lateral clavicle and also acts to stabilize the clavicle. |
This muscle aids in respiration, medially rotates the scapula, protracts the scapula, and also draws the scapula inferiorly. |
Most of its actions flex and rotate the head. In regards to the shoulder, however, it also aids in respiration by elevating the sternoclavicular joint when the head is fixed. |
It is capable of rotating the scapula downward and elevating the scapula. |
They are responsible for downward rotation of the scapula with the levator scapulae, as well as adduction of the scapula. | ||
Different portions of the fibers perform different actions on the scapula: depression, upward rotation, elevation, and retraction. | ||
levator scapulae | Arises from the transverse processes of cervical vertebrae 1-4, and attaches to the upper part of the inner border of the scapula. | Elevates the scapula. |
latissimus dorsi | A large muscle that arises from the spinous processes of the lower six thoracic vertebrae, lumbar and all sacral vertebrae, and posterior iliac crest. It attaches to the intertubercular groove of the humerus. | Adducts, extends and rotates the humerus inwards. |
The following describes the terms used for different movements of the shoulder:
Scapular retraction (aka scapular adduction) | The scapula is moved posteriorly and medially along the back, moving the arm and shoulder joint posteriorly. Retracting both scapulae gives a sensation of "squeezing the shoulder blades together." | rhomboideus major, minor, and trapezius |
Scapular protraction (aka scapular abduction) | The opposite motion of scapular retraction. The scapula is moved anteriorly and laterally along the back, moving the arm and shoulder joint anteriorly. If both scapulae are protracted, the scapulae are separated and the pectoralis major muscles are squeezed together. | serratus anterior (prime mover), pectoralis minor and major |
Scapular elevation | The scapula is raised in a shrugging motion. | levator scapulae, the upper fibers of the trapezius |
Scapular depression | The scapula is lowered from elevation. The scapulae may be depressed so that the angle formed by the neck and shoulders is obtuse, giving the appearance of "slumped" shoulders. | pectoralis minor, lower fibers of the trapezius, subclavius, latissimus dorsi |
Arm abduction | Arm abduction occurs when the arms are held at the sides, parallel to the length of the torso, and are then raised in the plane of the torso. This movement may be broken down into two parts: True abduction of the arm, which takes the humerus from parallel to the spine to perpendicular; and upward rotation of the scapula, which raises the humerus above the shoulders until it points straight upwards. | True abduction: supraspinatus (first 15 degrees), deltoid; Upward rotation: trapezius, serratus anterior |
Arm adduction | Arm adduction is the opposite motion of arm abduction. It can be broken down into two parts: downward rotation of the scapula and true adduction of the arm. | Downward rotation: pectoralis minor, pectoralis major, subclavius, latissimus dorsi (same as scapular depression, with pec major replacing lower fibers of trapezius); True Adduction: latissimus dorsi, subscapularis, teres major, infraspinatus, teres minor, pectoralis major, long head of triceps, coracobrachialis. |
Arm flexion | The humerus is rotated out of the plane of the torso so that it points forward (anteriorly). | pectoralis major, coracobrachialis, biceps brachii, anterior fibers of deltoid. |
Arm extension | The humerus is rotated out of the plane of the torso so that it points backwards (posteriorly) | latissimus dorsi and teres major, long head of triceps, posterior fibers of the deltoid |
Medial rotation of the arm | Medial rotation of the arm is most easily observed when the elbow is held at a 90-degree angle and the fingers are extended so they are parallel to the ground. Medial rotation occurs when the arm is rotated at the shoulder so that the fingers change from pointing straight forward to pointing across the body. | subscapularis, latissimus dorsi, teres major, pectoralis major, anterior fibers of deltoid |
Lateral rotation of the arm | The opposite of medial rotation of the arm. | infraspinatus and teres minor, posterior fibers of deltoid |
Arm circumduction | Movement of the shoulder in a circular motion so that if the elbow and fingers are fully extended the subject draws a circle in the air lateral to the body. In circumduction, the arm is not lifted above parallel to the ground so that "circle" that is drawn is flattened on top. | pectoralis major, subscapularis, coracobrachialis, biceps brachii, supraspinatus, deltoid, latissimus dorsi, teres major and minor, infraspinatus, long head of triceps |
When this type of cartilage starts to wear out (a process called arthritis), the joint becomes painful and stiff.
Conventional x-rays and ultrasonography are the primary tools used to confirm a diagnosis of injuries sustained to the rotator cuff. For extended clinical questions, imaging through Magnetic Resonance with or without intraarticular contrast agent is indicated.
Hodler et al. recommend starting scanning with conventional x-rays taken from at least two planes, since this method gives a wide first impression and even has the chance of exposing any frequent shoulder pathologies, i.e., decompensated rotator cuff tears, tendinitis calcarea, dislocations, fractures, usures, and/or osteophytes. Furthermore, x-rays are required for the planning of an optimal CT or MR image.Hodler J et al.. Gelenkdiagnostik mit bildgebenden Verfahren. Stuttgart etc.. G. Thieme. 1992.
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.
This projection has a low tolerance for errors and, accordingly, needs proper execution. The Y-projection can be traced back to Wijnblath’s 1933 published cavitas-en-face projection.
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.Thelen M. et al.. Radiologische Diagnostik der Verletzungen von Knochen und Gelenken. Stuttgart etc.. Georg Thieme. 1993.
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 intensifiedcrass 1984 @Katthagen BD. et al.. Schultersonographie. Stuttgart. 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.
In addition, a dynamic examination can help to differentiate between an ultrasound artifact and a real pathology.Hedtmann A. et al.. Atlas und Lehrbuch der Schultersonographie. Stuttgart. 1988@ Hodler J et al.. Gelenkdiagnostik mit bildgebenden Verfahren. Stuttgart etc.. G. Thieme. 1992.
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.Katthagen BD. et al.. Schultersonographie. Stuttgart.
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.Nové-Josserand L, Gerber C, Walch G (1997) Lesions of the antero-superior rotator cuff. Lippincott-Raven, Philadelphia
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.
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.
==Additional images==
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