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THE SHOULDER[br]00.00[br]The best way for us to learn about the upper extremity is to begin at the very[br]beginning, right up here. We'll start by looking at the bones of the shoulder region:[br]the clavicle, the scapula and the humerus. Then we'll look at the joints that let them[br]move, and the muscles, which make them move. Lastly we'll look at the principal[br]blood vessels and nerves in the region. First, the bones.[br]00.30[br]BONES, JOINTS AND LIGAMENTS[br]The bones that connect the upper extremity to the trunk are the clavicle, or collar[br]bone, and the scapula, or shoulder blade. The parts of them that we can feel[br]beneath beneath the skin can be seen in this dissection: here's the spine of the[br]scapula, here's the clavicle. In the dry skeleton, here's the clavicle, here's the[br]scapula.[br]01.00[br]The proximal long bone of the upper extremity, the humerus articulates with the[br]scapula at the shoulder joint. The scapula and clavicle articulate with the bones of[br]the thorax at one point only, here, at the sternoclavicular joint.[br]01.19[br]The lateral end of the clavicle articulates with this projection on the scapula, the[br]acromion, forming the acromio-clavicular joint. Apart from this one very movable[br]bony linkage, the scapula is held onto the body entirely by muscles. It's thus[br]capable of a wide range of movement, upward and downward, and also forward and[br]backward around the chest wall.[br]01.50[br]Looking at the clavicle from above we can see that it's slightly S-shaped, with a[br]forward curve to its medial half. At its medial end this large joint surface articulates[br]with the sternum. At the lateral end this smaller surface articulates with the scapula.[br]On the underside, massive ligaments are attached, here laterally and here medially.[br]02.21[br]The scapula is a much more complicated bone. The flat part, or blade, is roughly[br]triangular with an upper border, a lateral border, and a medial border. The blade[br]isn't really flat, it's a little curved to fit the curve of the chest wall.[br]2.42[br]This smooth concave surface is the glenoid fossa. It's the articular surface for the[br]shoulder joint. Above and below the glenoid fossa are the supraglenoid tubercle, and[br]the infraglenoid tubercle, where two tendons are attached as we'll see.[br]03.02[br]A prominent bony ridge, the spine of the scapula, arises from the dorsal surface, and[br]divides it into the supraspinous fossa, and the infraspinous fossa. At its lateral end[br]the spine gives rise to this flat, angulated projection, the acromion, which stands[br]completely clear of the bone. The clavicle articulates with the scapula here, at the[br]tip of the acromion. This other projection, looking like a bent finger, is the coracoid[br]process.[br]03.40[br]Here's how the clavicle and the scapula look in the living body. Round the edge of[br]the shallow glenoid fossa, a rim of fibrocartiilage, the glenoid labrum, makes the[br]socket of the shoulder joint both wider and deeper. This flat ligament, the coracoacromial[br]ligament, joins the coracoid process to the acromion. Here's the acromioACLAND'S[br]DVD ATLAS OF HUMAN ANATOMY VOL 1 PART 1 2[br]clavicular joint. Two strong ligaments, the trapezoid in front and the conoid behind,[br]fix the underside of the clavicle to the coracoid process. There's very little movement[br]at the acromio-clavicular joint.[br]04.16[br]As we've seen, the medial end of the clavicle articulates with the sternum at the[br]sterno-clavicular joint. Strong ligaments between the clavicle and the sternum and[br]between the clavicle and the underlying first rib, keep the two bones together but[br]permit an impresssive range of motion: up and down, and backward and forward.[br]04.42[br]Now let's see how the clavicle and the scapula move, relative to the trunk. Upward[br]movement of the scapula is called elevation; downward movement is called[br]depression. Forward movement around the trunk is called protraction; the opposite[br]movement is retraction. This movement is called upward rotation. The opposite[br]movement is downward rotation. In real life these movements of the scapula are[br]often combined.[br]05.16[br]The range of motion of the scapula provides fully one third of the total range of[br]motion of the humerus, relative to the body, sometimes more. Without this[br]movement of the scapula, we'd only be able to abduct our arm to here. That's as far[br]as the shoulder joint goes, before bone hits bone. It's scapular movement that lets[br]us get all the way to here.[br]05.41[br]Now let's look at the shoulder joint. To understand the shoulder joint, let's get[br]acquainted with the upper half of the humerus.[br]This is the head of the humerus. The articular surface is half of a sphere. On the[br]anterior aspect is a well marked groove known as the bicipital groove, because the[br]tendon of the long head of the biceps runs in it. At the proximal end of the groove[br]are the lesser tubercle, and the greater tubercle. Because it's between two[br]tubercles, the bicipital groove is also known as the inter-tubercular groove. Down[br]here on the lateral aspect of the humerus, almost halfway down the bone, is a rough[br]spot, the deltoid tubersosity.[br]06.21[br]Here's the shoulder joint, also known as the gleno-humeral joint. This loose sleeve[br]of tissue which encloses the joint is the joint capsule. The capsule doesn't hold the[br]bones together, it's quite a weak structure. What it does is to permit movement.[br]The structures which hold the two bones together are muscles, as we'll see. Here's[br]the tendon of one of those muscles.[br]06.48[br]Let's look at the movements that can occur at the shoulder joint. Movement forward[br]and upward is called flexion. Movement downward and backward is called extension.[br]Movement away from the side of the body is ab-duction. The opposite movement is[br]ad-duction. Rotation which moves the front of the arm towards the body, is internal[br]rotation. Rotation the other way is external rotation.[br]07.23[br]Now that we've taken a look at the bones, joints and ligaments, let's spend about a[br]minute reviewing what we've seen so far.[br]07.30[br]REVIEW[br]Here's the clavicle, for an easy start. On the scapula here's the blade, the glenoid[br]fossa, the supraglenoid, and infraglenoid tubercles, the spine of the scapula, the[br]supraspinous and infraspinous fossa the acromion, and the coracoid process.[br]ACLAND'S DVD ATLAS OF HUMAN ANATOMY VOL 1 PART 1 3[br]07.57[br]Here's the proximal humerus, with the head, the greater tubercle and lesser[br]tubercle, the bicipital groove, and the deltoid tuberosity.[br]08.12[br]Here's the sterno-clavicular joint, and here's the acromio-clavicular joint, with the[br]conoid ligament and the trapezoid ligament.[br]08.24[br]On the scapula, here's the glenoid labrum, and the coraco-acromial ligament. Lastly,[br]here's the capsule of the shoulder joint[br]08.37[br]MUSCLES[br]Now let's move on to look at the muscles. We'll build our understanding pretty much[br]from the inside to the outside. First we'll look at the deepest muscles, the ones that[br]go from the scapula to the humerus. Then we'll look at the ones that go from the[br]trunk to the scapula, and lastly we'll look at the big three muscles on the outside,[br]which cover up almost all the others.