Glenoid

Glenoid cavity
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Costal surface of left scapula. Glenoid cavity shown in red.
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Glenoid cavity shown in red. This cavity articulates with the head of the humerus.
Latin cavitas glenoidalis, fossa glenoidalis
Gray's subject #50 207

The glenoid cavity (or glenoid fossa of scapula from Greek: gléne, "socket") is a part of the shoulder. It 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 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 with in the glenoid cavity by means of the long head of the bicep 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 also reinforces this joint more specifically with the supraspinatus 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 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 (hip-joint) the glenoid cavity is relatively shallow. This makes the shoulder joint prone to luxation. Strong ligaments and muscles prevents luxation in most cases.

By being so shallow the glenoid cavity allows the glenohumeral joint to have the greatest mobility of all joints in the body, allowing 120 degrees of unassisted flexion. This is also accomplished by the great mobility of the scapula (shoulder blade).

The Glenoid Cavity is also the point of origin for the muscle: Triceps Brachii.

Evolution

Interpretations of the fossil remains of Australopithecus africanus (STS 7) and A. afarensis (AL 288-1; a.k.a. Lucy) 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 adaptations in these hominoid primates, whereas the lateral orientation of the glenoid in modern humans reflects the typical lowered position of the arm. [1]

In dinosaurs

In dinosaurs the main bones of the pectoral girdle were the scapula (shoulder blade) and the coracoid, both of which directly articulated with the clavicle. The place on the scapula where it articulated with the humerus (upper bone of the forelimb) is the called the glenoid. The glenoid is important because it defines the range of motion of the humerus.[2]

Additional images

Notes

This article incorporates text from a public domain edition of Gray's Anatomy.

References

  • ANATOMY & PHYSIOLOGY: THE UNITY OF FORM AND FUNCTION, SIXTH EDITION Published by McGraw-Hill Written by Kenneth Saladin
  • http://www.ucsfhealth.org/conditions/glenoid_labrum_tear/index.html

See also

External links

  • Diagram at cerrocoso.edu
  • 03:02-07
  • eMedicine Dictionary
  • Mechanics of Glenohumeral Instability at University of Washington Department of Orthopaedics
de:Schulterblatt#Cavitas glenoidalis
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