Shoulder
Encyclopedia
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 joint
s. The major joint of the shoulder is the glenohumeral joint
, which "shoulder joint" generally refers to. In human anatomy
, the shoulder joint comprises the part of the body where the humerus
attaches to the scapula
, the head sitting in the glenoid fossa
. The shoulder is the group of structures in the region of the joint.
There are two kinds of cartilage in the joint. The first type is the white cartilage on the ends of the bones (called articular cartilage) which allows the bones to glide and move on each other. When this type of cartilage starts to wear out (a process called arthritis), the joint becomes painful and stiff. The labrum is a 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 shoulder must be mobile enough for the wide range actions of the arms and hands, but also stable enough to allow for actions such as lifting, pushing and pulling. The compromise between mobility and stability results in a large number of shoulder problems
not faced by other joints such as the hip
.
s of the shoulder: The glenohumeral, acromioclavicular, and the sternoclavicular joints.
is the main joint of the shoulder and the generic term "shoulder joint" usually refers to it. 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. It is formed by the articulation between the head of the humerus and the lateral scapula (specifically-the glenoid fossa of the scapula). The "ball" of the joint is the rounded, medial anterior surface of the humerus and the "socket" is formed by the glenoid fossa
, the dish-shaped portion of the lateral scapula. The shallowness of the fossa and relatively loose connections between the shoulder and the rest of the body allows the arm to have tremendous mobility, at the expense of being much easier to dislocate than most other joints in the body. Approximately its 4 to 1 disproportion between the large head of the humerus and the shallow glenoid cavity.
The 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.
There is also a ligament
called semicirculare humeri which is a transversal band between the posterior sides of the tuberculum minus and majus of the humerus. This band is one of the most important strengthening ligaments of the joint capsule
. The shoulder is a vital joint and critical for movement.
or top most portion of the sternum. The clavicle is triangular and rounded and the manubrium is convex; the two bones articulate. The joint consists of a tight capsule and complete intra-articular disc which ensures stability of the joint. The costoclavicular ligament is the main limitation to movement, therefore, the main stabilizer of the joint. A fibrocartilaginous disc present at the joint increases the range of movement. Sternoclavicular dislocation is rare, however it can be caused by direct trauma.
, making it one of the most mobile joints in the human body. The shoulder can abduct
, adduct
(such as during the shoulder fly
), rotate, be raised in front of and behind the torso
and move through a full 360° in the sagittal plane
. This tremendous range of motion also makes the shoulder extremely unstable, far more prone to dislocation
and injury than other joints
The following describes the terms used for different movements of the shoulder:
.
is an anatomical term given to the group of muscles and their tendons that act to stabilize the shoulder. It is composed of the tendons and muscles (supraspinatus
, infraspinatus
, teres minor
and subscapularis
) that hold the head of the humerus (ball) in the glenoid fossa (socket).
Two filmy sac-like structures called bursa
e permit smooth gliding between bone, muscle, and tendon. They cushion and protect the rotator cuff from the bony arch of the acromion.
, are one of the more common reasons for physician visits for musculoskeletal symptoms. The shoulder is the most movable joint in the body. However, it is an unstable joint because of the range of motion allowed. This instability increases the likelihood of joint injury, often leading to a degenerative process in which tissues break down and no longer function well.
Major injuries to the shoulder include rotator cuff tear
and bone fracture
s of one or more of the bones of the shoulder.
Shoulder fractures include:
forelimb are characterised by a high degree of mobility in the shoulder-thorax connection. Lacking of 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 connect the shoulder girdle to the trunk in some animals; the coracoid bone in reptiles and birds, and the clavicle
in primate
s and bat
s; but cursorial
mammals lack this bone.
In primates, the shoulder shows characteristics the differs 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.
Clavicle
In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...
(collarbone), the scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
(shoulder blade), and the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
(upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joint
Joint
A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...
s. The major joint of the shoulder is the glenohumeral joint
Glenohumeral joint
The glenohumeral joint, or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula and the head of the humerus...
, which "shoulder joint" generally refers to. In human anatomy
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...
, the shoulder joint comprises the part of the body where the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
attaches to the scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
, the head sitting in the glenoid fossa
Glenoid fossa
Glenoid fossa can refer to:* Glenoid cavity * Mandibular fossa...
. The shoulder is the group of structures in the region of the joint.
There are two kinds of cartilage in the joint. The first type is the white cartilage on the ends of the bones (called articular cartilage) which allows the bones to glide and move on each other. When this type of cartilage starts to wear out (a process called arthritis), the joint becomes painful and stiff. The labrum is a 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 shoulder must be mobile enough for the wide range actions of the arms and hands, but also stable enough to allow for actions such as lifting, pushing and pulling. The compromise between mobility and stability results in a large number of shoulder problems
Shoulder problems
Shoulder problems including pain, are one of the more common reasons for physician visits for musculoskeletal symptoms. The shoulder is the most movable joint in the body. However, it is an unstable joint because of the range of motion allowed...
not faced by other joints such as the hip
Hip (anatomy)
In vertebrate anatomy, hip refer to either an anatomical region or a joint.The hip region is located lateral to the gluteal region , inferior to the iliac crest, and overlying the greater trochanter of the femur, or "thigh bone"...
.
Joints
There are three jointJoint
A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...
s of the shoulder: The glenohumeral, acromioclavicular, and the sternoclavicular joints.
Glenohumeral joint
The glenohumeral jointGlenohumeral joint
The glenohumeral joint, or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula and the head of the humerus...
is the main joint of the shoulder and the generic term "shoulder joint" usually refers to it. It is a ball and socket joint
Ball and socket joint
A ball and socket joint is a joint in which the distal bone is capable of motion around an indefinite number of axes, which have one common center...
that allows the arm to rotate in a circular fashion or to hinge out and up away from the body. It is formed by the articulation between the head of the humerus and the lateral scapula (specifically-the glenoid fossa of the scapula). The "ball" of the joint is the rounded, medial anterior surface of the humerus and the "socket" is formed by the glenoid fossa
Glenoid cavity
The glenoid cavity is a shallow pyriform, articular surface, which is located on the lateral angle of the scapula. It is directed laterally and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest.This cavity forms the...
, the dish-shaped portion of the lateral scapula. The shallowness of the fossa and relatively loose connections between the shoulder and the rest of the body allows the arm to have tremendous mobility, at the expense of being much easier to dislocate than most other joints in the body. Approximately its 4 to 1 disproportion between the large head of the humerus and the shallow glenoid cavity.
The capsule
Joint capsule
An articular capsule is an envelope surrounding a synovial joint.-Layers:Each capsule consists of two layers:* an outer layer composed of avascular white fibrous tissue...
is a soft tissue envelope that encircles the glenohumeral joint and attaches to the scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
, humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
, and head of the biceps
Biceps
Biceps may refer to:*Biceps brachii muscle, a muscle located on the inside of the upper arm*Biceps femoris muscle, one of the hamstring muscles of the back of each thigh*Biceps , a point in a metrical pattern...
. 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.
There is also a ligament
Ligament
In anatomy, the term ligament is used to denote any of three types of structures. Most commonly, it refers to fibrous tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.Ligament can also refer to:* Peritoneal...
called semicirculare humeri which is a transversal band between the posterior sides of the tuberculum minus and majus of the humerus. This band is one of the most important strengthening ligaments of the joint capsule
Joint capsule
An articular capsule is an envelope surrounding a synovial joint.-Layers:Each capsule consists of two layers:* an outer layer composed of avascular white fibrous tissue...
. The shoulder is a vital joint and critical for movement.
Sternoclavicular joint
The sternoclavicular occurs at the medial end of the clavicle with the manubriumManubrium
The manubrium or manubrium sterni is the broad, upper part of the sternum. Located ventrally with a quadrangular shape, wider superiorly and narrower inferiorly, it articulates with the clavicles and the first two ribs.-Borders:The superior border is the thickest and presents at its center the...
or top most portion of the sternum. The clavicle is triangular and rounded and the manubrium is convex; the two bones articulate. The joint consists of a tight capsule and complete intra-articular disc which ensures stability of the joint. The costoclavicular ligament is the main limitation to movement, therefore, the main stabilizer of the joint. A fibrocartilaginous disc present at the joint increases the range of movement. Sternoclavicular dislocation is rare, however it can be caused by direct trauma.
Movements
The muscles and joints of the shoulder allow it to move through a remarkable range of motionRange of motion
Range of motion , is the distance that a movable object may normally travel while properly attached to another object. It is also called range of travel, particularly when talking about mechanical devices and in mechanical engineering fields...
, making it one of the most mobile joints in the human body. The shoulder can abduct
Abduction (kinesiology)
Abduction, in functional anatomy, is a movement which draws a limb away from the median plane of the body. It is thus opposed to adduction.-Upper limb:* of arm at shoulder ** Supraspinatus** Deltoid* of hand at wrist...
, adduct
Adduction
Adduction is a movement which brings a part of the anatomy closer to the middle sagittal plane of the body. It is opposed to abduction.-Upper limb:* of arm at shoulder ** Subscapularis** Teres major** Pectoralis major** Infraspinatus...
(such as during the shoulder fly
Fly (exercise)
A fly is a strength training exercise in which the hand and arm move through an arc while the elbow is kept at a constant angle. Flyes are used to work the muscles of the upper body...
), rotate, be raised in front of and behind the torso
Torso
Trunk or torso is an anatomical term for the central part of the many animal bodies from which extend the neck and limbs. The trunk includes the thorax and abdomen.-Major organs:...
and move through a full 360° in the sagittal plane
Sagittal plane
Sagittal plane is a vertical plane which passes from front to rear dividing the body into right and left sections.-Variations:Examples include:...
. This tremendous range of motion also makes the shoulder extremely unstable, far more prone to dislocation
Dislocation (medicine)
Joint dislocation, or luxation , occurs when bones in a joint become displaced or misaligned. It is often caused by a sudden impact to the joint. The ligaments always become damaged as a result of a dislocation...
and injury than other joints
The following describes the terms used for different movements of the shoulder:
| Name | Description | Muscles |
|---|---|---|
| Scapular retraction (aka adduction of the scapula) | 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 abduction of the scapula) | 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: same as downward rotation with addition of teres major and the lowest fibers of the deltoid |
| 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 |
Major muscles
The muscles that are responsible for movement in the shoulder attach to the scapula, humerus, and clavicle. The muscles that surround the shoulder form the shoulder cap and underarmUnderarm
-Axillary intertrigo:Excessive perspiration can result in axillary intertrigo. Intertrigo is an inflamed skin condition caused by heat, friction, and moisture. A warm, wet armpit may accommodate the growth of pathogenic bacteria, yeasts, and fungi. The condition is responsible for rash-like...
.
| Name | Attachment | Function |
| serratus anterior | Originates on the surface of the upper eight ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula. | It fixes the scapula into the thoracic wall and aids in rotation and abduction of the shoulders. |
| subclavius | Located inferior to the clavicle, originating on the first rib First rib The first rib is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward, and its borders inward and outward.... and inserting (penetrating) on the subclavian groove Subclavian groove On the medial part of the clavicle is a broad rough surface, the costal tuberosity , rather more than 2 cm. in length, for the attachment of the costoclavicular ligament. The rest of this surface is occupied by a groove, which gives attachment to the Subclavius; the coracoclavicular fascia, which... of the clavicle. |
It depresses the lateral clavicle and also acts to stabilize the clavicle. |
| pectoralis minor | Arises from the third, fourth, and fifth ribs, near their cartilage and inserts into the medial border and upper surface of the coracoid process of the scapula. | This muscle aids in respiration, medially rotates the scapula, protracts the scapula, and also draws the scapula inferiorly. |
| sternocleidomastoid | Attaches to the sternum (sterno-), the clavicle Clavicle In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally... (cleido-), and the mastoid process Mastoid process The mastoid process is a conical prominence projecting from the undersurface of the mastoid portion of the temporal bone. It is located just behind the external acoustic meatus, and lateral to the styloid process... of the temporal bone Temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis... of the skull. |
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. |
| levator scapulae | Arises from the transverse processes of the first four cervical vertebrae Cervical vertebrae In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also... and inserts into the medial border of the scapula. |
It is capable of rotating the scapula downward and elevating the scapula. |
| rhomboid major and rhomboid minor (work together) | They arise from the spinous processes of the thoracic vertebrae Thoracic vertebrae In human anatomy, twelve thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. They are intermediate in size between those of the cervical and lumbar regions; they increase in size as one proceeds down the spine, the upper... T1 to T5 as well as from the spinous processes of the seventh cervical. They insert on the medial border of the scapula, from about the level of the scapular spine to the scapula's inferior angle. |
They are responsible for downward rotation of the scapula with the levator scapulae, as well as adduction of the scapula. |
| trapezius | Arises from the occipital bone Occipital bone The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself... , the ligamentum nuchae, the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebrae, and from the corresponding portion of the supraspinal ligament. It inserts on the lateral clavicle, the acromion process Acromion process The acromion process, or simply the acromion , is an anatomical feature on the shoulder blade , together with the coracoid process extending laterally over the shoulder joint.-In humans:... , and into the spine of the scapula. |
Different portions of the fibers perform different actions on the scapula: depression, upward rotation, elevation, and adductions. |
| deltoid Deltoid muscle In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central... , anterior fibers |
Arises from the anterior border and upper surface of the lateral third of the clavicle Clavicle In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally... . |
The anterior fibres are involved in shoulder abduction when the shoulder is externally rotated. The anterior deltoid is weak in strict transverse flexion but assists the pectoralis major during shoulder transverse flexion / shoulder flexion (elbow slightly inferior to shoulders). |
| deltoid Deltoid muscle In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central... , middle fibers |
Arises from the lateral margin and upper surface of the acromion. | The middle fibres are involved in shoulder abduction when the shoulder is internally rotated, are involved in shoulder flexion when the shoulder is internally rotated, and are involved in shoulder transverse abduction (shoulder externally rotated) -- but are not utilized significantly during strict transverse extension (shoulder internally rotated). |
| deltoid Deltoid muscle In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central... , posterior fibers |
Arises from the lower lip of the posterior border of the spine of the scapula, as far back as the triangular surface at its medial end. | The posterior fibres are strongly involved in transverse extension particularly since the latissimus dorsi muscle Latissimus dorsi muscle The latissimus dorsi , meaning 'broadest muscle of the back' , is the larger, flat, dorso-lateral muscle on the trunk, posterior to the arm, and partly covered by the trapezius on its median dorsal region.The latissimus dorsi is responsible for extension,... is very weak in strict transverse extension. The posterior deltoid is also the primary shoulder hyperextensor. |
Rotator cuff
The rotator cuffRotator cuff
In anatomy, the rotator cuff is the group of muscles and their tendons that act to stabilize the shoulder. The four muscles of the rotator cuff, along with the teres major muscle, the coracobrachialis muscle and the deltoid, make up the seven scapulohumeral muscles of the human body.-Function:The...
is an anatomical term given to the group of muscles and their tendons that act to stabilize the shoulder. It is composed of the tendons and muscles (supraspinatus
Supraspinatus muscle
The supraspinatus is a relatively small muscle of the upper arm that runs from the supraspinatous fossa superior of the scapula to the greater tubercle of the humerus. It is one of the four rotator cuff muscles and also abducts the arm at the shoulder...
, infraspinatus
Infraspinatus muscle
In human anatomy, the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa. As one of the four muscles of the rotator cuff, the main function of the infraspinatus is to externally rotate the arm and stabilize the shoulder joint.-Origin and...
, teres minor
Teres minor muscle
The teres minor is a narrow, elongated muscle of the rotator cuff.-Origin:It arises from the dorsal surface of the axillary border of the scapula for the upper two-thirds of its extent, and from two aponeurotic laminæ, one of which separates it from the infraspinatus muscle, the other from the...
and subscapularis
Subscapularis muscle
The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint.-Origin and insertion:...
) that hold the head of the humerus (ball) in the glenoid fossa (socket).
Two filmy sac-like structures called bursa
Bursa (anatomy)
A bursa is a small fluid-filled sac lined by synovial membrane with an inner capillary layer of slimy fluid . It provides a cushion between bones and tendons and/or muscles around a joint. This helps to reduce friction between the bones and allows free movement...
e permit smooth gliding between bone, muscle, and tendon. They cushion and protect the rotator cuff from the bony arch of the acromion.
Medical problems
Shoulder problems including painPain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
, are one of the more common reasons for physician visits for musculoskeletal symptoms. The shoulder is the most movable joint in the body. However, it is an unstable joint because of the range of motion allowed. This instability increases the likelihood of joint injury, often leading to a degenerative process in which tissues break down and no longer function well.
Major injuries to the shoulder include rotator cuff tear
Rotator cuff tear
Rotator cuff tears are tears of one or more of the four tendons of the rotator cuff muscles. A rotator cuff injury can include any type of irritation or damage to the rotator cuff muscles or tendons....
and bone fracture
Bone fracture
A bone fracture is a medical condition in which there is a break in the continuity of the bone...
s of one or more of the bones of the shoulder.
Shoulder fractures include:
- Clavicle fractureClavicle fractureA clavicle fracture is a bone fracture in the clavicle, or collarbone. It is often caused by a fall onto an outstretched upper extremity, a fall onto a shoulder, or a direct blow to the clavicle...
- Scapular fractureScapular fractureA scapular fracture is a fracture of the scapula, the shoulder blade. The scapula is sturdy and located in a protected place, so it rarely breaks. When it does, it is an indication that the individual was subjected to a considerable amount of force and that severe chest trauma may be present. ...
- Proximal humerus fractureHumerus fractureA humerus fracture can be classified by the location of the humerus involved: the upper end, the shaft, or the lower end.Certain lesions are commonly associated with fractures to specific areas of the humerus. At the upper end, the surgical neck of the humerus and anatomical neck of humerus can...
Evolutionary variation
TetrapodTetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
forelimb are characterised by a high degree of mobility in the shoulder-thorax connection. Lacking of 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 connect the shoulder girdle to the trunk in some animals; the coracoid bone in reptiles and birds, and the clavicle
Clavicle
In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...
in primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s and bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...
s; but cursorial
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...
mammals lack this bone.
In primates, the shoulder shows characteristics the differs 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
See also
- Shoulder girdle (Pectoral girdle)
- Glenohumeral jointGlenohumeral jointThe glenohumeral joint, or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula and the head of the humerus...
(Shoulder joint) - Acromioclavicular jointAcromioclavicular jointThe acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion and the clavicle. -Function:...
- Sternoclavicular joint
- Chip on shoulderChip on shoulderOne carries a chip on one's shoulder as a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight. The concept is now metaphorical, describing people who nurse a grudge or grievance that readily provokes fury or disputation.-History:"A chip on the shoulder"...