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SHOULDER ANATOMY

Bones
Muscles
Joints and Ligaments


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BONY ANATOMY


     SHOULDER JOINT

	-A ball and socket jt.
	-A mobile jt.

     Anatomical considerations:
     1.  Articulation of the ball that is spherical to a shallow glenoid 
          fossa
     2.  Weak ligaments
     3.  Shoulder capsule is loose and redundant
     4.  There is an intimate relationship bet. Bursa, tendons, capsule 
           and ligament.
     5.  Forms mobile base of the shoulder jt. the SCAPULA (only
           connection via coracoacromial ligament and acromioclavicular 
           lig.

 -  Bones of the shoulder complex are the humerus, which articulates
    with the scapula at the glenoid fossa, the clavicle, which originates 
    at the sternum and follows and S shape to the tip of the shoulder 
    where it articulates with the acromion process of the scapula which 
    is a somewhat flat triangular bone with two bony projections called 
    the spine of the scapula and the coracoid process. 
 -  The spine of the scapula divides the posterior aspect of the scapula 
    into two unequal parts called the supraspinatus fossa, which holds
    the supraspinatus muscle and the infraspinatus fossa which holds
    the infraspinatus muscle
 -  The shoulder or pectoral girdle consists of articulations between 
    the clavicle, scapula and the proximal end of the humerus. 
 -  The sternoclavicular articulationis the only bony link between the 
    upper limb and the axial skeleton. 
 -  Movements at this joint are largely passive in that the occur as a 
    result of active movements of the scapula. 
 -  Through the acromioclavicular articulation, the clavicle can act as a 
    strut maintaining the upper limb away from the thorax permitting a
    greater range of upper limb motion. 
 -  This joint also helps provide static stability to the upper limb 
    reducing the need to use muscle energy to keep the upper limb in 
    its proper alignment. 
 -  The glenohumeral articulation (shoulder joint) has the
    greatest range of motion of any joint in the body. 
 -  The mobility of the shoulder joint is necessary for placement of 
    the hand to maximize manipulation.
 -  The scapula is suspended on the thoracic wall by muscle
    forming a "functional joint" called the scapulothoracic joint. 
 -  These muscles act to stabilize and/ or to actively move the scapula.
 -  Active movements of the scapula help increase the range of motion
    of the shoulder joint. 
	
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MUSCLES OF THE SHOULDER


A. Extrinsic - Suspend scapula from the trunk .Stabilize 
       and/or actively moves scapula 
            1.	Trapezius 
            2.	Levator Scapulae 
            3.	Rhomboid Major and Minor 
            4.	Serratus Anterior 
            5.	Pectoralis minor 

B. Intrinsic - Attach scapula to humerus 
            1.	Deltoid 
            2.	Teres Major 
            3.	Rotator Cuff (active stabilization of shoulder joint) 
                            a.	Supraspinatus 
                            b.	Infraspinatus 
                            c.	Teres Minor 
                            d.	Subscapularis 

C. Attach trunk to humerus 
            1.	Latissimus dorsi 
            2.	Pectoralis Major 

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JOINTS AND LIGAMENTS


1. Acromioclavicular Joint 
      - Planar type joint between lateral portion of the clavicle and 
          the acromion of the scapula. 

     1. Ligaments 
            a.	Acromioclavicular 
            b.	Coracoclavicular 
            c.	Conoid 
            d.	Trapezoid 
     2. Functions 
            - Bind clavicle to scapula supporting weight of upper limb 
                  minimizing use of muscle energy 
     3. Shoulder Separation 
            - Tearing of acromioclavicular and /or coracoclavicular 
                  ligaments 
            a.	Clavicle overrides acromion 
            b.	Weight of upper limb pulls scapula and acromion 
                   inferiorly below clavicle 

2. Sternoclavicular Joint 
      - Sellar joint between the medial end of the clavicle and the 
           manubrium of the sternum. 

     1. Ligaments 
             a .Sternoclavicular 
             b. anterior and posterior 
             c. Interclavicular 
             d. Costoclavicular 
      2. Fibrocartilage Disc 
            -  Strengthens articulation 

3. Glenohumeral ( Shoulder ) Joint 
      - Ball and socket articulation between head of humerus and 
            glenoid cavity. 
      - Favors mobility over stability 

C. Glenohumeral Joint 
      1. Capsule 
         - Attaches from glenoid cavity to anatomical neck of humerus 
          a. Least amount of support inferiorly 
      2. Ligaments 
          a. Coracoacromial 
                - Helps resist upward displacement of the head of the 
                    humerus 
          b.Coracohumeral 
                - Strengthens superior portion of capsule 
                - Some support during shoulder abduction 
          c.Transverse Humeral Ligament 
                - holds long head of biceps in the groove 
          d. Glenohumeral Ligaments - 3 parts all attach from upper 
                    margin of glenoid cavity and strengthen anterior
                    portion of capsule 
                1. Superior - over the humeral head to a depression
                           above the lesser tuberosity 
                2. Middle - in front of humerus to lower lesser 
                           tuberosity 
                3. Inferior - to lower part of the anatomical neck 
      3.Rotator Cuff Muscles 
            - Active stabilizers of shoulder joint 
            - act throughout entire range of motion at shoulder 
         a.Depress head of humerus in glenoid cavity when humerus 
               moves 
            - Prevents compression of structures between humeral head 
               and acromion 
         b.Muscles also help rotate shoulder 

4. Scapulothoracic "Joint" 
      - Scapula suspended on rib cage by muscles 
      - highly mobile 
      - Scapula movements increases range of motion at the shoulder 
            joint 

     1. Stability 
      - Dependent upon activity of extrinsic muscles 
        a.Winged scapula 
     2. Alignment 
      - Upwardly rotated and elevated position of scapula at rest 
      - action of trapezius muscle 

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