Part of the shoulder
The
glenoid fossa
of the scapula or the
glenoid cavity
is a bone part of the
shoulder
. The word
glenoid
is pronounced
or
(both are common) and is from
Greek
:
glene
, "socket", reflecting the shoulder joint's
ball-and-socket
form.
[1]
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 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
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
(at the hip-joint) the glenoid cavity is relatively shallow. This makes the
shoulder joint
prone to
dislocation
(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
. Additional range of motion in shoulder flexion (typically up to 180 degrees in humans) is also accomplished by the great mobility of the
scapula
(shoulder blade) through a process known as scapulohumeral rhythm.
[2]
Evolution
[
edit
]
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.
[3]
In dinosaurs
[
edit
]
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 called the glenoid. The glenoid is important because it defines the range of motion of the humerus.
[4]
Additional images
[
edit
]
See also
[
edit
]
Notes
[
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]
References
[
edit
]
This article incorporates text in the
public domain
from
page 207
of the 20th edition of
Gray's Anatomy
(1918)
References
[
edit
]
- Larson, Susan G. (2009). "Evolution of the Hominin Shoulder: Early
Homo
". In Grine, Frederick E.; Fleagle, John G.; Leakey, Richard E. (eds.).
The First Humans ? Origin and Early Evolution of the Genus
Homo
. Vertebrate Paleobiology and Paleoanthropology. Springer.
doi
:
10.1007/978-1-4020-9980-9
.
ISBN
978-1-4020-9979-3
.
- ANATOMY & PHYSIOLOGY: THE UNITY OF FORM AND FUNCTION, SIXTH EDITION Published by McGraw-Hill Written by Kenneth Saladin
- "Glenoid Labrum Tear"
.
ucsfhealth.org
.
Archived
from the original on 2012-11-23
. Retrieved
2012-12-13
.
External links
[
edit
]