Structures of the Shoulder Region (Nursing)

by Darren Salmi, MD, MS

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    00:01 So that finally brings us to a ball and socket joint known as the shoulder joint.

    00:06 The shoulder joint has a lot of components to it though. We'll start with the distal components which begin with the humerus.

    00:15 The typical long bone of the upper portion of our upper limb which is actually what we call the arm.

    00:22 The arm isn't everything from shoulder to fingertip. It's actually just the part between our shoulder and our elbow.

    00:28 So our arm bone is really the humerus and at the proximal end, we have the humeral head.

    00:35 And this humeral head is covered in articular cartilage because it's going to participate at a joint and the cavity that this humeral head is going to fit into is something called the glenoid cavity and it's the shallow depression of a bone called the scapula. The scapula has a bunch of other parts and one part we can see way up top coming up and pointing towards us is the acromion.

    01:04 Acro means highest or uppermost and that's how it gets this name.

    01:08 It's the uppermost projection of the scapula and then connecting to that is a bone you probably heard called the collar bone. It's an easily palpable bone but we tend to call it the clavicle.

    01:22 We also have a lot of muscles here that you probably have heard of before that provide a lot of structural stability to the joint called rotator cuff muscles and they're going to attach from the scapula to bumps or tuberosities that exist on the humerus.

    01:42 And if you were to look at an x-ray of the shoulder joint, you would see some of those structures but it might look kind of empty to you and you might think that the humerus looks like it's just sort of floating.

    01:52 And it's not really connected right up to these bones and that's because not everything in the joint is going to show up in an x-ray because not everything is going to be bone.

    02:02 For example, we have cartilage which is radiolucent or invisible on x-rays.

    02:07 Same thing with those rotator cuff muscles that are going to provide support.

    02:12 They're going to be invisible but we know they're there providing stability at this joint.

    02:19 So what kind of movements can we have at the shoulder joint? Well, there's some of the ones that we've already talked about in the introduction.

    02:27 So from the anatomic position, moving the humerus more medially is going to be adduction bringing it closer to the body, moving it away is going to be abduction.

    02:42 And once we get past the horizontal point, it rotates a little bit so that we can keep going and at that point we call it elevation.

    02:53 So we can essentially get another 90 degrees and raise that arm almost a full 180 degrees.

    03:03 Now, let's take a lateral point of view to see some other movements.

    03:06 If we were to move our arm backwards at the shoulder joint or posteriorly, that would be extension or retroversion, and moving it anteriorly where we can move it quite a bit further, we will call that anteversion or flexion.

    03:24 We'll rotate to a superior point of view to see rotation a little bit better and we know that if we rotate towards the midline, that would be internal or medial rotation.

    03:39 If we rotate outward, that's going to be lateral or external rotation.

    03:44 There is generally less movement here, about 45 degrees at least in each direction.

    03:53 So what about some muscles in this area? So the first is right over that shoulder joint and it's called the deltoid muscles and delta is sort of a triangular shape and that's why it's called deltoid.

    04:07 It refers to its shape and this is going to be our major abductor at this shoulder joint.

    04:14 We also have a muscle running from the scapula to the ribs that's a fairly minor one called pectoralis minor.

    04:20 It's not called minor because it doesn't do much.

    04:22 It's because it's smaller than the big boy over here, the pec major.

    04:27 Pectoralis major is our big-time adductor although can also do extension and internal rotation as well.

    04:37 We also have some really large back muscles that we saw on the back lecture that we mentioned didn't really act on the back per se but really acted on the upper limb.

    04:46 To revisit those, we had the trapezius and that was the one that helps us shrug our shoulders because it attaches to the scapula.

    04:55 The wide flat latissimus dorsi which is another major adductor and then we also have some muscles that are a little smaller and do sort of unique function.

    05:07 These are the serratus anterior on the ribs but they attach from the ribs to the scapula and they pull the scapula forward as if you were punching forward and that's called protraction of your scapula.

    05:23 Then we have some smaller back muscles. Fortunately, this first one tells you what it does.

    05:30 The levator scapulae is going to elevate or raise the scapula.

    05:37 We have the rhomboids which are going from the medial edge of the scapula to the vertebral column.

    05:43 They're going to have the opposite effect of the serratus anterior and they're going to retract the scapula and pull it closer to the vertebra. And then we have one called the teres major.

    05:56 Now, I'll stop here because teres is probably an unfamiliar word. Teres just means round so it's more of a descriptive term.

    06:05 And when you see a major, that usually means there's going to be a minor somewhere and it turns out that teres minor is one of the rotator cuff muscles but it's important to point out that the teres major, although it's a very helpful adductor and can help with internal rotation, isn't actually one of the rotator cuff muscles because it's not in the same location as the other ones.

    06:28 So here are the nice posterior view of the scapula and its little bump that we call the spine and that's going to help us understand these first rotator cuff muscle names.

    06:39 We have the supraspinatus above it and we have the infraspinatus below it.

    06:45 They're crossing over that shoulder joint to reach those tuberosities on the humerus.

    06:50 And as you can tell maybe by this orientation, when they contract, it's going to pull the shoulder joint in such a way that it's going to cause lateral rotation. Along with that other muscle we mentioned, the teres minor.

    07:05 Again, not to confuse the two, it's still a round muscle and it's still going out towards the upper limb but this is actually attaching to those tuberosities so it is actually one of your rotator cuff muscles.

    07:20 If we swing around to an anterior point of view, we see that all this anterior surface of the scapula is filled in by our last rotator cuff muscle, the subscapularis and this is on the opposite side as those other muscles so we can kind of deduce that they're going to cause medial rotation.

    About the Lecture

    The lecture Structures of the Shoulder Region (Nursing) by Darren Salmi, MD, MS is from the course Anatomy of the Musculoskeletal System (Nursing).

    Included Quiz Questions

    1. Humerus
    2. Humeral head
    3. Glenoid cavity
    4. Femur
    5. Patella
    1. Adduction
    2. Abduction
    3. Elevation
    4. Inversion
    5. Pronation
    1. Deltoid
    2. Pectoralis minor
    3. Pectoralis major
    4. Soleus
    5. Sartorius
    1. Supraspinatus
    2. Infraspinatus
    3. Teres minor
    4. Soleus
    5. Pectoralis major

    Author of lecture Structures of the Shoulder Region (Nursing)

     Darren Salmi, MD, MS

    Darren Salmi, MD, MS

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