Shoulder - WikiHQ

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.

Structure

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.

Joint

thumb|250px|Cross-section of shoulder joint

The shoulder joint (also known as the glenohumeral joint) is the main joint of the shoulder.

The four tendons 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.

The following describes the terms used for different movements of the shoulder:

{| class="wikitable"

! Name

! Description

! Muscles

| 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

| 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

| 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

| 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

| 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

Development

Puberty

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

Clinical significance

thumb|200px|left|Anatomical studies of the shoulder by [[Leonardo da Vinci (ca.1510)]]

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

Fracture

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

Pain

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. but other parts of the rotator cuff may also be involved. There are different severities of a rotator cuff tear, which range from a partial tear to a full-thickness tear. A partial tear is when the tendon is thinned, but still connected to the bone. Full-thickness tears can be separated into two classes: a full-thickness incomplete tear or a full-thickness complete tear. The incomplete tear is characterized by having only a portion of the tendon disconnected from the bone, where the complete tear has the tendon completely separated off the bone. For all forms of rotator cuff tears, depending on the severity of the injury, possible treatments include rest, an arm sling, physical therapy, steroid injections, and non-steroidal anti-inflammatory drugs, or surgery.

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.

X-ray

Projectional radiography views of the shoulder include:

;AP-projection 40° posterior oblique after Grashey

The body has to be rotated about 30 to 45 degrees towards the shoulder to be imaged, and the standing or sitting patient lets the arm hang. This method reveals the joint gap and the vertical alignment towards the socket.

CR. shoulder x-ray, a.p..jpg|CR. shoulay film.

Transaxillary CR shoulder.jpg|alt=A Transaxillary conventional radiography|Transaxillary conventional radiography

Y CR shoulder.jpg|alt=A Y-projection conventional radiography|Y-projection conventional radiography

</gallery>

Ultrasound

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.

| thumb|upright|alt=Longitudinal ultra sonography of the supraspinatus tendon|Longitudinal ultra sonography of the supraspinatus tendon

| thumb|upright|alt=Transversal ultra sonography of the supraspinatus tendon|Transversal ultra sonography of the supraspinatus tendon

MRI

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.

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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.

Other animals

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.

Additional images

File:Gray326.png|The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula