Illustrated Encyclopedia of Human Anatomic Variation: Opus V: Skeletal Systems: Upper Limb
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
The scapular notch is frequently bridged by bone rather than a ligament (5% of cases studied), converting it into a foramen which is normal in some animals.
Accessory notches may be present; one frequently is found on the inferior angle.
The acromion may fail to unite. In about 5% of individuals (more commonly males), the separate part (os acromion) is on the right side.
Fascicles of the subclavius muscle may be inserted onto the coracoid process by passing through the clavipectoral fascia.
The tendon of m. pectoralis minor, in part (15%) or entirely (1%) , may pass over the coracoid process to insert elsewhere. As a result, it may produce a characteristic groove on the superior part of the process. A bursa intervening between the tendon and bone may communicate with the shoulder joint (Seib).
The coracoid process may exist as a separate bone.
Sulcus for Circumflex Scapular Artery
One hundred sixty-seven (14.5%) of a total of 1,152 scapulae from the
dissecting room exhibited no sulcus for the circumflex scapular
artery. Contrasted with the observations of Kajava who found the
sulcus was absent more often than it was present in Finns. In 130
scapulae he found it present 47 times on the left side, and 34 times
on the right. Vallois reported the incidence of the vascular sulcus
was somewhat higher. In French scapulae he found it in 64% on the
right side and 61.7% on the left side--the absence between 35 to
40%.
Scapular Foramina
Considered to be rare, Gruber (1871, 1877) described only three
cases. In 180 scapulae of known age and sex, Vallois found only one
produced by fracture. In his collection of 795, he found seven
scapulae with foramina. Gray studied 1,151 scapulae with 28
possessing foramina. Three of 87 Indian scapulae had foramina.
Costal Facets
Gruber (1864,1872) reported that sometimes there is a protuberance
located on the scapula related to the "bursa mucosa anguli superioris
scapulae". Fontan described a pair of scapulae, which possessed two
costal facts each. They articulated with the posterior surfaces of
the third and seventh ribs, respectively, and had associated with
them both a capsule and synovial membrane. Kajava reported four
instances of costal facets. Vallois found 13 costal facets in 180
(7.2%) scapulae. Gray found costal facets in 64 of 1,152 (5.55%)
scapulae. Only two of 87 Indian scapulae had costal facets at the
superior angle of the left scapula.
Suprascapular Foramina
The conversion of the suprascapular notch into a foramen as a result
of the ossification of the supraspinous ligament was found in three
of 60 (5%) scapulae by Poirier and Chasrpy. In 133 Finnish scapulae
studied by Kajava the foramen was present only twice (1.5%). Vallois
found the foramina to occur 13 times in 200 (6.5%) scapulae of
Frenchmen. In a second study Vallois reported that Italian scapulae
had foramina in 6.1% and in a series of scapulae from various sources
the incidence varied from 0% to 3.3%. Gray found foramen in 73 of
1,151 scapulae (6.34%). No suprascapular foramina were found in 87
Indian scapulae.
Shape of Acromion
The shapes of the acromial processes have been classified (Macalister
1893) as to whether they were falciform, triangular, quadrangular, or
intermediate in form. Of 1,080 scapulae 507 (46.9%) possessed
acromions which could be classified as falciform. Five hundred
forty-four of the 1,080 were left scapulae and among these the
falciform type of acromion was found 277 times. The 536 right
scapulae had falciform acromions 230 times. These percentages are
higher than those found by Kajava who found the falciform type to
occur in 5.7% of 121 scapulae, and of Vallois who reported 14% of 157
French scapulae to have acromial processes of falciform shape.
Three hundred thirty-four of the 1,080 acromial processes were triangular. Of these, 137 were on the left side and 167 were on the right side. Gray's figures are again somewhat higher than those of Kajava (8.3%) and of Vallois (19.7%). Triangular acromial processes occurred in both bones of pairs 58 times from a total of 334 paired scapulae.
Among the 1,080 scapulae Gray found 214 (19.8%) acromial processes that he classified as quadrangular. One hundred five of the 544 left acromions were of this type, as were 109 of the 536 from the right side. These results of Gray do not correspond to those of Kajava who found quadrangular acromions in 55.8% or of those of Vallois, 26.1%.
An intermediate or non-characteristic shape of the acromial processes was evident in 55 (5.1%) of 1,080 scapulae. Both Kajava and Vallois assigned an intermediate or non-characteristic shape to a higher number (percentage) of acromions; 30.6% and 40.1% respectively.
All of the 80 Indian scapulae Gray examined had acromial processes that could be classified. There were 30 (30.5%) falciform, 49 (61.2%) and 1 (1.25%) was quadrangular.
Separate Acromial Bones
Separate acromial bones have been reported by Gruber (1863), LaGrange
(1882), Poirier (1887), Struthers (1895, 1896), Neumann (1918) and
Gray, (1942). These were descriptive studies. Symington (1900) found
5 separate acrominal bones in 40 subjects (6.25%). Vallois (1925)
studied 235 scapulae and found separate acromial processes in 2.1%.
In 1932, Vallois reported separate acromial processes occurring 19
times in 681 scapulae (2.7%). Gray (1942) reported 36 separate
acromial bones in 1,086 scapulae. He also reported agreement with
Vallois that separate acromial processes occur twice as frequently
unilaterally as bilaterally. Gray also reported that 83 Indian
scapulae had 3 unattached acromial processes; two 40 right scapulae
and once in 43 left scapulae.
Facets on Interior Surface of Acromion
Gray (1942) reported 240 (22.12%) scapular facets in 1,085 specimens.
One hundred-eleven facets from 547 specimens were on left scapulae
and 129 factes were of 538 right scapulae.
Of 334 pairs, 29 left and 40 right scapulae showed facets on one side alone. Forty-six pairs showed facets on both the left and right sides. The facets on 22 pairs were identical with each other in size and other characteristics. Among 80 Indian scapulae acromial facets were found 5 times. They occurred twice in 38 right scapulae and three times in 42 left scapulae.
Shape of the Glenoid Fossa
The shapes of the glenoid fossae were classified on the basis of
whether they were pyriform, round, oval or unclassifiable. The
largest number of scapulae examined exhibited pyriform glenoid fossae
(1,062/1,149--92.4%). One 5/1,149 (4%) glenoid fossae were found. In
78 of 1,149 (6.8%) scapulae the glenoid fossae were oval in form.
Only 4 of 1,149 (0.3%) could not be classfied as pyriform, round or
oval. Gray (1942) reported that the glenoid fossae were pyriform in
86 of 87 Indian scapulae. One left scapula showed on oval type.
Notchof Glenoid Lip
Kajava (1924) found the notch of the glenoid lip to be absent in
10.3% of 117 scapulae of Finns. In 180 French scapulae, Vallois
(1932) reported the notch present in all but 7. Gray (1942) found the
notch absent from the glenoid lip 265 times in 1,150 scapulae
(23.04%) from the dissecting room. He also reported that among the 87
Indian scapulae, 15 showed no notch of the glenoid lip.
Vertebral Border
Gray states that according to Graves (1910) classification of the
vertebral border, that among 1,151 scapulae 706 were convex, 239 were
straight and 114 were concave, and two were unclassifiable. Among 580
left scapulae the convex vertebral border was present 363 times, the
straight 162 times, and the concave 54 times. Among 87 Indian
scapulae the convex vertebral border was noted 77 times, the straight
9 times, and the concave once.
A plate of bone extending from the medial margin of the scapula to the vertebral column has been reported (Ingersoll).
Incidences in per cent among paired scapulae from dissecting room.
Characteristic Common to both scapulae Left scapulae only Right scapulae only Absence of muscular cristae 1.1 1.9 0.5 Absence of sulcus for circumflex scapular artery 5.7 6.5 9.2 Anomalous scapular foramina .3 1.9 2.7 Presence of costal facets 2.2 5.4 3.0 Presence of suprascapular foramina 3.5 4.6 3.2 Schap of acromial process Falciform 33.8 18.3 10.2 Triangular 17.4 6.6 13.2 Quadrangular 11.7 8.1 7.5 Intermediate 2.4 3.0 3.6 Separate acromial bones 1.2 0.9 1.5 Facets on interior surface of acromion 13.8 8.7 12.0 Shape of glenoid fossa Pyriform 88.1 2.4 3.2 Round 0.0 0.8 0.3 Oval 2.2 3.0 5.1 Unclassifiable 0.3 0.0 0.0 Absence of notch of glenoid lip 11.1 9.5 15.7 Reactions at margins of glenoid fossae 20.3 8.7 9.8
From Gray, 1942.
Os Acromiale
Ossification of Acromion Process
Various Types of Acromion Process
Scapular Facets
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