Synonyms: shoulder blade, omoplate
German: Scapula, Schulterblatt
The
scapula forms the posterior part of the bony
shoulder girdle. It is a predominantly flat, triangular bone, which mainly serves as muscle’s origin and has a loose-jointed connection with humerus and collarbone (
clavicle).
The dorsal surface of the scapula is subdivided by the
spina scapulae into the smaller ]]supraspinatous fossa]] and the larger
infraspinous fossa. The origin of the
supraspinatus is in the
supraspinatous fossa. The
infraspinous fossa below the spine is to a large extent covered by the infraspinatus, which originates in the medial 2/3 of the fossa. On its lateral side – separated by a
fibrous septum – is situated the origin of the
teres major and
teres minor muscles.
The ventral surface of the scapula facing the ribs presents a broad concavity, which is the subscapular fossa. The medial 2/3 of the fossa are marked by oblique ridges, which serve as tendinous insertions of the
subscapularis. The subscapular fossa is separated from the vertebral border by smooth triangular areas at the medial and inferior angles. The
serratus anterior is inserted here.
The superior border is the shortest ridge of the scapula. It extends from the medial angle to the base of the coracoid process. There is a deep notch visible, termed the scapular notch, spanned by the superior transverse ligament. The formed incision gives passage to the
suprascapular nerve. The adjacent part of the superior border affords the attachment to the
omohyoideus.
The axillary border is the most massive of all 3 borders of the scapula. It begins at the lower margin of the glenoid cavity and ends at the inferior angle. Immediately below the glenoid cavity is a rough impression, the infraglenoid tuberosity. It gives origin to the long head (caput longum) of the
triceps brachii.
The vertebral border is the longest ridge of the scapula. It extends from the medial to the inferior angle. The vertebral border affords attachment to numerous muscles, among them the
rhomboideus major,
rhomboideus minor and
levator scapulae muscles.
The medial angle is formed by the junction of the vertebral and superior borders. It is thin, smooth and rounded and serves as attachment to a few fibers of the levator scapulae.
The inferior angle is formed by the junction of the vertebral and lateral borders. It is thick and rough. Its dorsal surface serves as attachment to the
teres major and some fibers of the
latissimus dorsi.
The lateral angle is the thickest part of the scapula and is sometimes called the "head of the scapula". It is a shallow, articular cavity covered by cartilage, called the glenoid cavity, which articulates with the head of the humerus.
The
spina scapulae is a compact plate of bone, which obliquely crosses the dorsal surface of the scapula and topographically separates the supraspinatous fossa from the infraspinatous fossa. It begins in a relatively flat area at the vertical border with a smooth, triangular surface, over which the tendon for insertion of the caudal part of the
trapezius glides. Toward the lateral, the
spine gradually elevates and ends in the
acromion, which overhangs the shoulder joint. The trapezius is attached to the superior part of the spine, and the
deltoid to the inferior part.
The
coracoid process is a strong hook-shaped process of the scapula. It originates above the glenoid cavity, initially extends
cranially and
medially, and then projects
ventrally and
laterally. It tapers on the way. The conjoined tendon of origin of the short head of the [[biceps brachii]) and
coracobrachialis muscles are attached to the coracoid process. In addition, it provides attachment to the
pectoralis minor and several ligaments.
The
acromion projects from the spina scapulae and forms the summit of the shoulder blade. Its superior surface is rough and serves, together with the lateral ridge of the acromion, as origin to the
deltoideus. The bone lies directly
subcutaneous and can be
palpated for anatomical reference. At the vertebral border of the acromion lies a small oval surface, which creates the articulation with the
collarbone (
clavicle). This joint is called acromioclavicular joint.
The
glenoid cavity is an oval articular cavity covered by cartilage, whose diameter has a larger extent vertically than horizontally. It forms the
humeroscapular articulation together with the head of the humerus. It is covered by the
glenoid lip that increases the depth of the cavity. Above the articular cavity lies the
supraglenoid tubercle. It gives origin to the long head of the biceps brachii.
