Scapula. In anatomy, the scapula (plural scapulae or scapulas)[1] or shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones the scapulae are paired, with the scapula on the left side of the body being roughly a mirror image of the right scapula. In early Roman times, people thought the bone resembled a trowel, a small shovel. The shoulder blade is also called omo in Latin medical terminology. The scapula forms the back of the shoulder girdle. In humans, it is a flat bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage. Structure[edit] It is a wide, flat bone lying on the thoracic wall that provides an attachment for three different groups of muscles.
The head, processes, and the thickened parts of the bone, contain cancellous tissue; the rest consists of a thin layer of compact tissue. Surfaces[edit] Front Back There is a ridge on the outer part of the back of the scapula. Side Borders[edit] Coracoid process. "Coracoid" in itself means "like a raven's beak", with reference to its shape. (Greek "Korax" = Raven) Structure[edit] The coracoid process is a thick curved process attached by a broad base to the upper part of the neck of the scapula; it runs at first upward and medialward; then, becoming smaller, it changes its direction, and projects forward and lateralward.
The ascending portion, flattened from before backward, presents in front a smooth concave surface, across which the Subscapularis passes. The horizontal portion is flattened from above downward; its upper surface is convex and irregular, and gives attachment to the Pectoralis minor; its under surface is smooth; its medial and lateral borders are rough; the former gives attachment to the Pectoralis minor and the latter to the coracoacromial ligament; the apex is embraced by the conjoined tendon of origin of the Coracobrachialis and short head of the Biceps brachii and gives attachment to the coracoclavicular fascia.
Function[edit] Lateral border of the scapula. The lateral border (or axillary border, or margin) is the thickest of the three borders of the scapula. It begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and backward to the inferior angle. Immediately below the glenoid cavity is a rough impression, the infraglenoid tuberosity, about 2.5 cm. in length, which gives origin to the long head of the Triceps brachii; in front of this is a longitudinal groove, which extends as far as the lower third of this border, and affords origin to part of the Subscapularis.
The inferior third is thin and sharp, and serves for the attachment of a few fibers of the Teres major behind, and of the Subscapularis in front. Additional images[edit] Left scapula. References[edit] This article incorporates text from a public domain edition of Gray's Anatomy. External links[edit] Medial border of scapula. The medial border of the scapula (vertebral border, medial margin) is the longest of the three borders, and extends from the superior to the inferior angle. It is arched, intermediate in thickness between the superior and the axillary borders, and the portion of it above the spine forms an obtuse angle with the part below.
This border presents an anterior and a posterior lip, and an intermediate narrow area. The anterior lip affords attachment to the Serratus anterior; the posterior lip, to the Supraspinatus above the spine, the Infraspinatus below; the area between the two lips, to the Levator scapulæ above the triangular surface at the commencement of the spine, to the Rhomboideus minor on the edge of that surface, and to the Rhomboideus major below it; this last is attached by means of a fibrous arch, connected above to the lower part of the triangular surface at the base of the spine, and below to the lower part of the border.
Additional images[edit] Left scapula. See also[edit] Inferior angle of the scapula. The inferior angle of the scapula is formed by the union of the medial and lateral border of the scapula and is the lowest part of the scapula. It is thick and rough and its posterior (or back) surface affords attachment to the teres major and frequently to a few fibers of the latissimus dorsi muscle. The anatomical plane that passes vertical through the inferior angle of the scapula is named the scapular line. An abnormal protruding inferior angle of the scapula or winged scapula can be caused by a serratus anterior paralysis.
Additional images[edit] Left scapula. Inferior angle shown in red.Animation. See also[edit] References[edit] This article incorporates text from a public domain edition of Gray's Anatomy. External links[edit] Spine of scapula. The spine of the scapula or scapular spine is a prominent plate of bone, which crosses obliquely the medial four-fifths of the scapula at its upper part, and separates the supra- from the infraspinatous fossa. Structure[edit] It begins at the vertical border by a smooth, triangular area over which the tendon of insertion of the lower part of the Trapezius glides, and, gradually becoming more elevated, ends in the acromion, which overhangs the shoulder-joint. The spine is triangular, and flattened from above downward, its apex being directed toward the vertebral border.
Root[edit] The root of the spine of the scapula is the most medial part of the scapular spine. The root of the spine is on a level with the tip of the spinous process of the third thoracic vertebra.[1] Left scapula. Function[edit] It presents two surfaces and three borders. Additional image[edit] Left scapula seen from behind (spine shown in red).Position of spine (shown in red). References[edit] External links[edit] Acromion. Structure[edit] The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid cavity.[1] Surfaces[edit] Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the deltoideus, and in the rest of its extent is subcutaneous.
Its inferior surface is smooth and concave.[1] Borders[edit] Variation[edit] There are three morphologically distinct types of acromia and a correlation between these morphologies and rotator cuff tear:[2] Os acromiale[edit] The acromion has four ossification centers called (from tip to base) pre-acromion, meso-acromion, meta-acromion, and basi-acromion. Four types of os acromiale can be distinguished:[5] Plan of ossification of the scapula. In other animals[edit] Additional images[edit] Left scapula. Notes[edit] External links[edit] Acromioclavicular joint. The acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle.[1] It is a plane synovial joint. Structure[edit] Ligaments[edit] The joint is stabilized by three ligaments: The acromioclavicular ligament, which attaches the clavicle to the acromion of the scapula.
Superior Acromioclavicular Ligament This ligament is a quadrilateral band, covering the superior part of the articulation, and extending between the upper part of the lateral end of the clavicle and the adjoining part of the upper surface of the acromion. It is composed of parallel fibers, which interlace with the aponeuroses of the Trapezius and Deltoideus; below, it is in contact with the articular disk when this is present. It is in relation, above, in rare cases with the articular disk; below, with the tendon of the Supraspinatus Variation[edit] Function[edit] Clinical significance[edit] Clavicle. Structure[edit] The clavicle is a doubly curved short bone that connects the arm (upper limb) to the body (trunk), located directly above the first rib.
It acts as a strut to keep the scapula in place so the arm can hang freely. Medially, it articulates with the manubrium of the sternum (breast-bone) at the sternoclavicular joint. At its lateral end it articulates with the acromion of the scapula (shoulder blade) at the acromioclavicular joint. It has a rounded medial end and a flattened lateral end. From the roughly pyramidal sternal end, each clavicle curves laterally and anteriorly for roughly half its length. It then forms a smooth posterior curve to articulate with a process of the scapula (acromion).
It can be divided into three parts: medial end, lateral end and shaft. Medial end[edit] The medial end is quadrangular and articulates with the clavicular notch of the manubrium sterni to form the sternoclavicular joint. It gives attachments to: Lateral end[edit] Shaft[edit] Variation[edit] Sternoclavicular articulation. The sternoclavicular articulation is structurally classed as a synovial double-plane joint and functionally classed as a diarthrotic joint.
It is composed of two portions separated by an articular disc which is made from fibrocartilage. The parts entering into its formation are the sternal end of the clavicle, the upper and lateral part of the manubrium sterni (clavicular notch of the manubrium sterni), and the cartilage of the first rib, visible from the outside as the suprasternal notch. The articular surface of the clavicle is much larger than that of the sternum, and is invested with a layer of cartilage, which is considerably thicker than that on the latter bone. Movement[edit] The sternoclavicular joint allows movement of the clavicle in three planes, predominantly in the anteroposterior & vertical planes, although some rotation also occurs. Ligaments[edit] See also[edit] References[edit] Jump up ^ Lippert, Lynn. External links[edit] Human sternum. The sternum (from Greek στέρνον, sternon, "chest"; plural "sternums" or "sterna") or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax (chest).
It connects to the rib bones via cartilage, forming the anterior section of the rib cage with them, and thus helps to protect the lungs, heart and major blood vessels from physical trauma. Although it is fused, the sternum can be sub-divided into three regions: the manubrium, the body, and the xiphoid process.[1] Structure[edit] The sternum is an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. The superior end supports the clavicles (collarbones), and its margins articulate with the cartilages of the first seven pairs of ribs. Its top is also connected to the sternocleidomastoid muscle. In its natural position, the inclination of the bone is oblique from above, downward and forward. Manubrium[edit] Body of sternum[edit] Fractures[edit] Supraspinatous fossa. The supraspinatous fossa (supraspinatus fossa, supraspinous fossa) of the posterior aspect of the scapula is smaller than the infraspinatous fossa, concave, smooth, and broader at its vertebral than at its humeral end.
Its medial two-thirds give origin to the Supraspinatus. References[edit] This article incorporates text from a public domain edition of Gray's Anatomy. See also[edit] Supraspinatus muscle External links[edit] Infraspinatous fossa. The infraspinatous fossa (infraspinatus fossa, infraspinous fossa) of the scapula is much larger than the supraspinatous fossa; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part.
The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle. Additional images[edit] Left scapula. Infraspinatous fossa shown in red.Animation. Infraspinatous fossa shown in red.Left scapula. External links[edit] Subscapular fossa. The costal or ventral surface of the scapula presents a broad concavity, the subscapular fossa.
It provides an attachment for the subscapularis muscle. Additional images[edit] Left scapula. Subscapular fossa shown in red.Animation. Subscapular fossa shown in red.Left scapula. Costal surface. References[edit] This article incorporates text from a public domain edition of Gray's Anatomy. External links[edit] Anterior view of left humerus. Bicipital Groove (intertubercular sulcus) Posterior view of left humerus.