The glenoid fossa of the scapula or the glenoid cavity is a bone part of the

shoulder 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 mak ...

. The word ''glenoid'' is pronounced or (both are common) and is from el, gléne, "socket", reflecting the shoulder joint's ball-and-socket form. It is a shallow, pyriform

articular The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two oth ...

surface, which is located on the lateral angle of the

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...

. 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 glenohumeral joint along with the humerus. This type of joint is classified as a synovial, ball and socket joint. The humerus is held in place within the glenoid cavity by means of the long head of the biceps tendon. This tendon originates on the superior margin of the glenoid cavity and loops over the shoulder, bracing humerus against the cavity. The

rotator cuff The rotator cuff is a group of muscles and their tendons that act to stabilize the human shoulder and allow for its extensive range of motion. Of the seven scapulohumeral muscles, four make up the rotator cuff. The four muscles are the supraspi ...

also reinforces this joint more specifically with the

supraspinatus The supraspinatus (plural ''supraspinati'') is a relatively small muscle of the upper back that runs from the supraspinous fossa superior portion of the scapula (shoulder blade) to the greater tubercle of the humerus. It is one of the four rotat ...

tendon to hold the head of the humerus in the glenoid cavity. The cavity surface is covered with cartilage in the fresh state, and its margins, slightly raised, give attachment to a

fibrocartilaginous Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these constituents, and its elasticity to the latter. It is the only type of ...

structure, the glenoid labrum, which deepens the cavity. This cartilage is very susceptible to tearing. When torn, it is most commonly known as a SLAP lesion which is generally caused by repetitive shoulder movements. Compared to the acetabulum (at the hip-joint) the glenoid cavity is relatively shallow. This makes the

shoulder joint The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'', shoulder) is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial joint ...

prone to

dislocation In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to s ...

(luxation). Strong glenohumeral ligaments and muscles prevents dislocation in most cases. By being so shallow the glenoid cavity allows the shoulder joint to have the greatest mobility of all joints in the body, allowing 120 degrees of unassisted

flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

. Additional range of motion in shoulder flexion (typically up to 180 degrees in humans) is also accomplished by the great mobility of the

(shoulder blade) through a process known as scapulohumeral rhythm.

Evolution

Interpretations of the fossil remains of '' Australopithecus africanus'' (STS 7) and '' A. afarensis'' (AL 288-1; a.k.a.

Lucy Lucy is an English feminine given name derived from the Latin masculine given name Lucius with the meaning ''as of light'' (''born at dawn or daylight'', maybe also ''shiny'', or ''of light complexion''). Alternative spellings are Luci, Luce, Lu ...

) suggest that the glenoid fossa was oriented more cranially in these species than in modern humans. This reflects the importance of overhead limb postures and suggests a retention of

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...

adaptations in these

hominoid Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its sister g ...

primates, whereas the lateral orientation of the glenoid in modern humans reflects the typical lowered position of the arm.

In dinosaurs

In dinosaurs the main bones of the

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of ...

were the

(shoulder blade) and the

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

, both of which directly articulated with the

clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the r ...

. The place on the scapula where it articulated with the humerus (upper bone of the forelimb) is called the glenoid. The glenoid is important because it defines the range of motion of the humerus.Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. .

Additional images

File:Glenoid cavity of left scapula - animation.gif, Left scapula. Glenoid cavity shown in red. File:Glenoid cavity of scapula - animation01.gif, Animation. Glenoid cavity shown in red. File:Gray328.png, Glenoid fossa of right side. File:Scapula ant numbered.png, Anterior view of left

showing glenoid cavity "2" File:Shoulder muscle - force couple of rotator cuff.gif, Animation of

. The muscles shown are

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. Structure It arises from its medial two-thirds and So ...

(at right),

infraspinatus muscle In human anatomy, the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa.''Gray's Anatomy'', see infobox. As one of the four muscles of the rotator cuff, the main function of the infraspin ...

(at top left),

teres minor muscle The teres minor (Latin ''teres'' meaning 'rounded') is a narrow, elongated muscle of the rotator cuff. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the ...

(at bottom left). File:Shoulder motion with rotator cuff (supraspinatus).gif, Animation of glenohumeral joint. The muscle shown is

supraspinatus muscle The supraspinatus (plural ''supraspinati'') is a relatively small muscle of the upper back that runs from the supraspinous fossa superior portion of the scapula (shoulder blade) to the greater tubercle of the humerus. It is one of the four rota ...

Notes

References

* * ANATOMY & PHYSIOLOGY: THE UNITY OF FORM AND FUNCTION, SIXTH EDITION Published by McGraw-Hill Written by Kenneth Saladin *

External links

Diagram at cerrocoso.edu
*

{{Authority control Shoulder Scapula

Evolution

In dinosaurs

Additional images

See also

Notes

References

References

External links