Prepladdder anatomy upper limb video 8
Category
📚
LearningTranscript
00:00We already have seen the movements of the scapula where we have described the
00:10scapula elevation, depression, lateral rotation and medial rotation. In this
00:15discussion we'll focus upon lateral rotation of the scapula because it is an
00:20important topic when we talk about shoulder abduction. Though it is
00:23basically the movement of the humerus bone away from the body that is what we
00:28call abduction at the shoulder joint but there is always associated movements of
00:33the scapula with the humerus plus even the clavicle at these two joints will be
00:39contributing for shoulder abduction. We know medially we have got the saddle
00:43synovial joint, the sternoclavicular joint and laterally it's a plain synovial
00:48joint, acromioclavicular joint. Both of them will be helping us in shoulder
00:53abduction. In here when we talk about the initiation of abduction 0 to 15 degree
00:58movement is chiefly contributed by a muscle over the scapula supraspinatus
01:04muscle while from 15 degree to 90 degree it is chiefly a deltoid muscle and
01:09beyond 90 degree if you want to move like an overhead abduction you need
01:14contribution by two muscles namely the trapezius and serratus anterior. Now be
01:18careful all these muscles which we have named may be supraspinatus, deltoid,
01:23trapezius or serratus they are all active throughout this movement of
01:27abduction. It is just that at a particular angle some of the muscles
01:31they become more active or chiefly active that means though the
01:36supraspinatus may be working for initial 0 to 15 degree chiefly but it remains in
01:41contraction throughout the movement of abduction and it applies to all the
01:45muscles during all the range of the movement. Now what about scapular
01:49movement in abduction? It is a ratio of 2 is to 1. Say if you are raising the
01:54humerus to 180 degree in that movement the humerus move by two units and one
02:00unit movement is contributed by scapular rotation which will be looking at one
02:04diagram as well. So what happens is normally the glenoid cavity of the
02:09scapula is facing laterally and hence the humerus cannot move beyond 90 degree of
02:14shoulder abduction. If you want to move the humerus beyond 90 degree you must be
02:19moving the glenoid cavity superiorly then only the humerus can move
02:24superiorly. So this movement of glenoid cavity facing more superior is done by
02:29lateral rotation of scapula contributed by the two muscles the trapezius and
02:33serratus. Let us look at this movement from the posterior view now. So this is
02:38the right shoulder joint but looking from the posterior view and talking
02:42about the lateral rotation of scapula overhead abduction these are the two
02:47muscles the trapezius and serratus anterior helping in lateral rotation of
02:52the scapula and elevating the glenoid cavity which normally looks to the
02:57lateral side but now they are going to elevate it and it will start looking
03:02superiorly taking the humerus bone beyond this 90 degree of abduction. So
03:07for more than 90 degree of abduction we must turn the glenoid cavity superior by
03:12this movement of lateral rotation of the scapula. Now what if I want to bring
03:17the humerus back a double de abduction then obviously we will have to make use
03:23of the other group of muscles the muscles which attach to the medial
03:27border of the scapula and can cause medial rotation of the scapula. So what
03:33are the names of the muscles which are working antagonistically to serratus
03:38and trapezius? As we have learnt the muscles attaching to medial border of
03:42scapula helping in medial rotation of scapula are the rhomboid muscles and the
03:49levator scapulae. They will not only do medial rotation they also help in the
03:54traction of scapula towards the midline and contributing to a double de
03:58adduction of the humerus at the shoulder joint. As we continue looking from the
04:03dorsal aspect of the scapular movements for the shoulder abduction we
04:08understand that if we are doing 180 degree of shoulder abduction then in
04:13this 180 degree of the movement the 60 degree has been contributed by the
04:18scapular movement that is lateral rotation of scapula, elevation of glenoid
04:23cavity and the remaining 120 degree is contributed by the humerus movement so
04:29the ratio is 1 is to 2 meaning the scapula has contributed for the 60
04:36degree of the range of movement whereas the humerus movement gave a contribution
04:41of 120 degree hence making it a total of 180 degree so that means whichever range
04:48the scapula is moving the humerus is moving double the amount of that 60 into
04:532 120 total 180 degree and remember in this 180 degree of shoulder abduction all
04:59the major muscles they remain in contraction though specifically some of
05:03them may be chiefly active in a particular range like we have mentioned
05:07what about the initiation of abduction the supraspinatus muscle how much degree
05:14it is more active as we mentioned 0 to 15 degree of abduction then what about
05:2015 to 90 degree of abduction lateral fibers of deltoid so deltoid is
05:26functional throughout the movement but chiefly from 15 to 90 degree of
05:31abduction and beyond that comes the serratus anterior working with trapezius
05:36so that they can do the overhead abduction that is 90 to 180 degree of
05:41abduction so beyond 90 degree to 180 degree which is required if you want to
05:46comb your hair so we need to remember these specific degrees because they come
05:51in the exam and they are clinically relevant as well as we look at this
05:56question it is asking us about a wrong statement for shoulder abduction which
06:02of the following movement does not occur when you are doing shoulder abduction so
06:08we will find the answer very quickly because when we are talking about
06:12shoulder abduction what we need is lateral rotation of scapula not the
06:17medial rotation and hence the answer to our question should be choice number a
06:22then we understand it is a wrong statement and medial rotation which is
06:28done by the thromboid muscle levator scapulae will be helping in a double d
06:33adduction at the shoulder joint not the abduction what about the elevation of
06:38humerus of course what exactly is shoulder abduction to move the humerus
06:43away from the body elevation of humerus that is shoulder abduction and is it the
06:48rotation of clavicular sternal joint happening is there a movement of
06:52acromioclavicular joint as we mentioned in the beginning of the discussion may
06:57it be the saddle-shaped sternoclavicular joint or plains anovial
07:01acromioclavicular joint both of them are helping in shoulder abduction so no
07:05problem with choice numbers G and D the only wrong option here is choice number
07:10A we have learned that it was the lateral rotation of scapula which will
07:14be then turning the laterally facing linoid cavity more superior with the
07:19help of trapezius and serratus anterior and helping us in overhead abduction so
07:25we'll keep our answer as choice number A here