Kinesiology of the Musculoskeletal System

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Kinesiology of the Musculoskeletal System

• Chapter 5
• Shoulder Complex

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Articulations of the Shoulder

• (SC) Sternoclavicular
• (AC) Acromioclavicular
• (ST) Scapulothoracic
• (GH) Glenohumeral

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Anatomical Orientation of the Shoulder Complex

• Clavicle - 20 degrees posterior to the frontal
  plane
• Scapula 35 degrees anterior to the frontal
  plane (scapular plane)
• Humerus 30 degrees posterior to the
  medial-lateral axis line

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Sternoclavicular Joint (SC)

• Clavicle
• Sternum
• 1st Rib
• Sternoclavicular ligaments
• Costoclavicular ligament
• Articular disc
• Muscular attachments

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SC Joint
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SC Joint (cont.)
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Osteokinematic Motions of the Clavicle
Elevation/Depression 45/10 degrees
Max Protraction/Retraction 15 to 30 degrees in
each direction Axial Rotation 40 to 50 degrees
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Acromioclavicular Joint (AC)

• Gliding or planar joint
• Articular disc
• Superior/Inferior AC joint capsule ligaments
• Coracoclavicular ligament

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AC Joint Separation
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AC Motions

• Upward
• Downward
• Rotation
• Horizontal
• Sagittal Plane
• Adjustments

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Scapulothoracic Joint (ST)

• Not a true joint
• Wide ROM of shoulder
• complex largely due to
• movement at ST joint
• ST motion AC motion SC motion

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Primary Movements of the Scapulothoracic Joint
(ST)

• Elevation/Depression
• Retraction/Protraction
• Downward Upward Rotation

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ST Elevation
ST Elevation SC joint elevation downward
rotation at AC joint
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ST Upward Rotation
ST Upward Rotation SC joint elevation upward
rotation at AC joint
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Glenohumeral Joint

• Humeral Head
• Glenoid Fossa of Scapula
• Glenoid Labrum
• Rotator Cuff Muscles (SITS)
• GH Joint Capsule
• Coracohumeral Ligament
• Long Head of Biceps
• Subacromial Space

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GH Joint Connective Tissues
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GH Joint
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GH Joint Stability

• Stability provided chiefly by the rotator cuff
  musculature and the fibrous capsule
• Rotator Cuff 4 muscles that blend into the
  joint capsule, providing stability and allowing
  for movement
• Capsular Ligaments ligaments that blend into
  the joint capsule, reinforcing the capsule and
  providing stability
• Glenoid Labrum fibrous cartilage extension of
  glenoid, deepens the glenoid fossa
• Long Head of Biceps attaches to supraglenoid
  tuberosity
• Coracohumeral ligaments thickening of the joint
  capsule

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GH stability (cont.)

• Static Stability provided by superior capsular
  structure, resting humeral head on upward sloping
  glenoid fossa, and negative pressure w/in GH
  joint
• Dynamic Stability provided by rotator cuff
  muscles dependent on normal resting length and
  functional strength of the SITS muscles

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GH Kinematics

• Flexion/Extension (120/45 deg)
• Abduction/Adduction (120 deg.)
• Internal/External Rotations (80/70 deg)
• Functional ROM greater in each direction due to
  contributions from AC, SC ST joints

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Rotator Cuff

• SITS muscles
• Supraspinatus
• Infraspinatus
• Teres Minor
• Subscapularis

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Rotator Cuff Dynamic GH Stabilizer
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Effects of Poor Scapular Stabilization

• Poor resting posture of scapula slightly
  protracted position
• Loss of upward or optimal tilt of scapula
• Loss of static stability of GH joint
• Inferior translation and internal rotation of
  humeral head
• Traction ischemia of rotator cuff musculature,
  especially supraspinatus
• Capsular laxity poor dynamic stabilization

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Scapular Stabilization (cont.)

• Serratus Anterior a fan shaped muscle that
  originates on the lateral surface of ribs 1-9,
  and inserts on the underside of the scapula,
  along the entire medial border
• Known as the Boxers Muscle because it is the
  primary protractor of the scapula

• The serratus anterior is an extremely important
  scapular stabilizer
• If the serratus is weak, or if the nerve
  supplying the muscle is injured, a winged
  scapula may result
• Functionally, if the scapula is not stable, the
  stability and functional strength of the rest of
  the shoulder complex is severely compromised

Winged Scapula
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Coracoacromial Arch Bursa

• 1 cm of space between acromion process and
  humeral head
• Arch contains supraspinatus, subacromial bursa,
  long head of the
• biceps, superior
• joint capsule
• Site of Impingement
• Syndrome

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Impingement Syndrome

• Activities that require forceful overhead actions
  often result impingement
• Fixed position military presses do not allow the
  proper rolling and gliding (translation) of the
  humeral head dumbell presses are more
  biomechanically sound

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Scapulohumeral Rhythm

• Synergistic coordination of scapulothoracic
  musculature producing abduction
• Combined motion of GH, AC, SC ST joints
• 21 ratio for every 3 degrees of shoulder
  abduction, 2 degrees occur at GH joint, and 1
  degree occurs at the ST joint (SC, AC)

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Scapulohumeral Rhythm (cont.)

• 0 90 degrees of abduction 60 deg of GH
  motion 30 degrees of ST motion
• ST abduction 20-25 degrees of clavicular
  elevation, 5-10 degrees of AC upward rotation
• 90-180 degrees of abduction 60 deg of GH
  motion 30 degrees of ST motion
• ST abduction 5 degrees of clavicular elevation,
• 25 degrees of AC upward rotation

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Scapulohumeral Rhythm Clinical Indications

• Rotator cuff pain in early phase of active
  abduction
• Impingement pain in mid phase of active abduction
• AC pain in late phase of active abduction

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Action of the Scapulothoracic Muscles

• Elevators Upper trapezius, levator scapula and
  to a lesser extent rhomboids
• Depressors Lower trapezius, latissimus dorsi,
  pectoralis minor, subclavius, serratus anterior

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Action of the Scapulothoracic Muscles (cont.)

• Protractors Serratus anterior, (pectoralis
  major by virtue of attachment on humerus)
• Retractors Mid lower trapezius, rhomboids
• Upward Rotators Serratus, upper, mid lower
  traps via force couple relationship

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Muscle Actions at GH Joint

• Abductors deltoid (3 divisions), supraspinatus
• Adductors pectoralis major, latissimus
  dorsi, teres major
• Internal Rotators pectoralis major,
  subscapularis, anterior deltoid, latissimus
  dorsi, teres major
• External Rotators infraspinatus, teres
  minor, posterior deltoid
• Flexors biceps brachii, coracobrachialis,
  anterior deltoid
• Extensors triceps brachii, posterior deltoid,
  latissimus dorsi, teres major

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References

• Neumann, D. Kinesiology of the Musculoskeletal
  System. 2002. Human Kinetics.