The scapula forms the posterior part of the bony shoulder girdle. It is a predominantly flat, triangular bone, which mainly serves as the origin for various muscles 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 supraspinous fossa and the larger infraspinous fossa. The origin of the supraspinatus muscle is in the supraspinous fossa. The infraspinous fossa, located below the spina scapulae, is to a large extent covered by the infraspinatus muscle, which originates in the medial 2/3 of the fossa. On its lateral side, separated by a fibrous septum, is the origin of the teres major and teres minor muscles.
The ventral surface of the scapula facing the ribs (costae) 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.
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