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Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,THE SHOULDER\N00.00\NThe best way for us to learn about the upper extremity is to begin at the very\Nbeginning, right up here. We'll start by looking at the bones of the shoulder region:\Nthe clavicle, the scapula and the humerus. Then we'll look at the joints that let them\Nmove, and the muscles, which make them move. Lastly we'll look at the principal\Nblood vessels and nerves in the region. First, the bones.\N00.30\NBONES, JOINTS AND LIGAMENTS\NThe bones that connect the upper extremity to the trunk are the clavicle, or collar\Nbone, and the scapula, or shoulder blade. The parts of them that we can feel\Nbeneath beneath the skin can be seen in this dissection: here's the spine of the\Nscapula, here's the clavicle. In the dry skeleton, here's the clavicle, here's the\Nscapula.\N01.00\NThe proximal long bone of the upper extremity, the humerus articulates with the\Nscapula at the shoulder joint. The scapula and clavicle articulate with the bones of\Nthe thorax at one point only, here, at the sternoclavicular joint.\N01.19\NThe lateral end of the clavicle articulates with this projection on the scapula, the\Nacromion, forming the acromio-clavicular joint. Apart from this one very movable\Nbony linkage, the scapula is held onto the body entirely by muscles. It's thus\Ncapable of a wide range of movement, upward and downward, and also forward and\Nbackward around the chest wall.\N01.50\NLooking at the clavicle from above we can see that it's slightly S-shaped, with a\Nforward curve to its medial half. At its medial end this large joint surface articulates\Nwith the sternum. At the lateral end this smaller surface articulates with the scapula.\NOn the underside, massive ligaments are attached, here laterally and here medially.\N02.21\NThe scapula is a much more complicated bone. The flat part, or blade, is roughly\Ntriangular with an upper border, a lateral border, and a medial border. The blade\Nisn't really flat, it's a little curved to fit the curve of the chest wall.\N2.42\NThis smooth concave surface is the glenoid fossa. It's the articular surface for the\Nshoulder joint. Above and below the glenoid fossa are the supraglenoid tubercle, and\Nthe infraglenoid tubercle, where two tendons are attached as we'll see.\N03.02\NA prominent bony ridge, the spine of the scapula, arises from the dorsal surface, and\Ndivides it into the supraspinous fossa, and the infraspinous fossa. At its lateral end\Nthe spine gives rise to this flat, angulated projection, the acromion, which stands\Ncompletely clear of the bone. The clavicle articulates with the scapula here, at the\Ntip of the acromion. This other projection, looking like a bent finger, is the coracoid\Nprocess.\N03.40\NHere's how the clavicle and the scapula look in the living body. Round the edge of\Nthe shallow glenoid fossa, a rim of fibrocartiilage, the glenoid labrum, makes the\Nsocket of the shoulder joint both wider and deeper. This flat ligament, the coracoacromial\Nligament, joins the coracoid process to the acromion. Here's the acromioACLAND'S\NDVD ATLAS OF HUMAN ANATOMY VOL 1 PART 1 2\Nclavicular joint. Two strong ligaments, the trapezoid in front and the conoid behind,\Nfix the underside of the clavicle to the coracoid process. There's very little movement\Nat the acromio-clavicular joint.\N04.16\NAs we've seen, the medial end of the clavicle articulates with the sternum at the\Nsterno-clavicular joint. Strong ligaments between the clavicle and the sternum and\Nbetween the clavicle and the underlying first rib, keep the two bones together but\Npermit an impresssive range of motion: up and down, and backward and forward.\N04.42\NNow let's see how the clavicle and the scapula move, relative to the trunk. Upward\Nmovement of the scapula is called elevation; downward movement is called\Ndepression. Forward movement around the trunk is called protraction; the opposite\Nmovement is retraction. This movement is called upward rotation. The opposite\Nmovement is downward rotation. In real life these movements of the scapula are\Noften combined.\N05.16\NThe range of motion of the scapula provides fully one third of the total range of\Nmotion of the humerus, relative to the body, sometimes more. Without this\Nmovement of the scapula, we'd only be able to abduct our arm to here. That's as far\Nas the shoulder joint goes, before bone hits bone. It's scapular movement that lets\Nus get all the way to here.\N05.41\NNow let's look at the shoulder joint. To understand the shoulder joint, let's get\Nacquainted with the upper half of the humerus.\NThis is the head of the humerus. The articular surface is half of a sphere. On the\Nanterior aspect is a well marked groove known as the bicipital groove, because the\Ntendon of the long head of the biceps runs in it. At the proximal end of the groove\Nare the lesser tubercle, and the greater tubercle. Because it's between two\Ntubercles, the bicipital groove is also known as the inter-tubercular groove. Down\Nhere on the lateral aspect of the humerus, almost halfway down the bone, is a rough\Nspot, the deltoid tubersosity.\N06.21\NHere's the shoulder joint, also known as the gleno-humeral joint. This loose sleeve\Nof tissue which encloses the joint is the joint capsule. The capsule doesn't hold the\Nbones together, it's quite a weak structure. What it does is to permit movement.\NThe structures which hold the two bones together are muscles, as we'll see. Here's\Nthe tendon of one of those muscles.\N06.48\NLet's look at the movements that can occur at the shoulder joint. Movement forward\Nand upward is called flexion. Movement downward and backward is called extension.\NMovement away from the side of the body is ab-duction. The opposite movement is\Nad-duction. Rotation which moves the front of the arm towards the body, is internal\Nrotation. Rotation the other way is external rotation.\N07.23\NNow that we've taken a look at the bones, joints and ligaments, let's spend about a\Nminute reviewing what we've seen so far.\N07.30\NREVIEW\NHere's the clavicle, for an easy start. On the scapula here's the blade, the glenoid\Nfossa, the supraglenoid, and infraglenoid tubercles, the spine of the scapula, the\Nsupraspinous and infraspinous fossa the acromion, and the coracoid process.\NACLAND'S DVD ATLAS OF HUMAN ANATOMY VOL 1 PART 1 3\N07.57\NHere's the proximal humerus, with the head, the greater tubercle and lesser\Ntubercle, the bicipital groove, and the deltoid tuberosity.\N08.12\NHere's the sterno-clavicular joint, and here's the acromio-clavicular joint, with the\Nconoid ligament and the trapezoid ligament.\N08.24\NOn the scapula, here's the glenoid labrum, and the coraco-acromial ligament. Lastly,\Nhere's the capsule of the shoulder joint\N08.37\NMUSCLES\NNow let's move on to look at the muscles. We'll build our understanding pretty much\Nfrom the inside to the outside. First we'll look at the deepest muscles, the ones that\Ngo from the scapula to the humerus. Then we'll look at the ones that go from the\Ntrunk to the scapula, and lastly we'll look at the big three muscles on the outside,\Nwhich cover up almost all the others.