Biomechanics of the Shoulder Girdle

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Biomechanics of the Shoulder Girdle

• PHYT 604

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Innervation of Scapular Region

• Name the Spinal Cord levels of innervation of
  scapular region and shoulder complex
• Identify Peripheral nerves
• Sensory dermatome v. peripheral nerve

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Dermatomes
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Peripheral Nerve Cutaneous
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Peripheral Nerve Cutaneous
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Joints Scapulo-Thoracic

• Location/ Supporting Structures
• Movements
• ABD, ADD, Upward Rotation, Downward Rotation,
  Protraction and Retraction

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Scapulo-Thoracic
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Scapulo-Thoracic Joint
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Scapulo-Thoracic Jt.
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Scapulo-Thoracic Jt.
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Plane of the Scapula

• With respect to the normal resting position of
  the scapula it lies on the rib cage
• It is at an angle of 30-45 degrees anterior to
  the bodies frontal plane

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Plane of the Scapula

• 30-45 degrees rotated anterior
• Tipped anteriorly 10 to 20 degrees
• Rotated 10 to 20 degrees upwardly

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Joints Sterno-Clavicular

• Saddle Norkin and Levangie
• Functionally acts as a ball in socket
• Movements Protraction/retraction,
  Elevation/depression, rotation
• Capsule/ligaments/disc
• Sternum concave cranial to caudal (elevation
  and depression) convex A-P Pro/retraction
• Clavicle convex cranial to caudal convex A-P
  therefore is a Sellar joint
• Close Pack Arm in Max. elevation
• Open Arm at side

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Sterno-Clavicular Joint
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Sterno-Clavicular Jt.
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Sterno-Clavicular Jt.
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Sterno-Clavicular Jt.
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Joints Continued

• Coraco-clavicular
• Type
• Capsule/ligaments
• Motions
• Pay special attention to the attachment and
  orientation of ligaments

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Coraco-Clavicular Joint
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Joints Continued

• Acromio-Clavicular
• Capsule/ligaments
• Note coraco-acromial arch
• Motions
• Initially, in development, a fibrous joint, joint
  space develops with use, leaves behind a small
  disc
• Ovoid, plane or gliding
• Acromionconcave clavicle convex
• Close packed g-h jt. _at_90degrees of ABD
• Open arm by side
• Motions Accessory

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A-C Joint
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Acromio-Clavicular Jt.
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A-C Joint Motions
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A-C Joint Motions
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Joints Continued

• Gleno-humeral
• Type
• Capsule/ligaments-gh/coraco-humeral
• Concave/convex surfaces ovoid
• Motions
• Close packed full abduction, external rotation
• Open 55 degrees of ABD, 30 degrees of
  Horizontal Abduction (Plane of the scapula)

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Gleno-Humeral Joint
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Gleno-Humeral Joint
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Gleno-Humeral Joint
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Gleno-Humeral Joint
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Gleno-Humeral Joint
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Gleno-Humeral Joint-Note Attachments of Rotator
Cuff
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Gleno-Humeral Joint
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Gleno-Humeral Joint
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Gleno-Humeral Ligaments
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Gleno-Humeral Ligaments Note Slackness when G-H
not in resting position
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Bursa
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Sub Deltoid Bursa
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Bursa
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Movements

• Scapulohumeral rhythm
• Purposes
• Motions at S-C joint
• Motions at A-C joint
• Motions at G-H joint
• Relative changes at Scapulo-thoracic

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Purposes

• Distribution of motion between 2 joints more
  ROM minimizing stability loss - Think GH and
  Scapulothoracic as the two joints
• Maintains glenoid fossa in optimum position to
  avoid contact of greater tubercle with acromion
  process arthrokinematics
• Places muscles in best length tension
  relationships by changing base of pull thru ROM
• For every two degrees of gleno-humeral motion
  there is 1 degree of scapular motion when total
  range is considered therefore 180 degrees of
  elevation 120 g-h and 60 scapular

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Scapulo-Humeral Rhythm
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Motions

• Scapular (scapulothoracic) motions during
  elevation of shoulder best described as
  protraction (ABD with upward rotation)
• Requires significant activity of
  sterno-clavicular as well as acromio-clavicular
  joint.
• First 30-45 degrees of elevation best described
  as the setting phase in terms of scapular
  motion as scapula seeks stability
• After that, motion is 2 to 1

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Motions at SC and AC

• During 1st 90º of elevation SC elevates
• Due to attachment of coracoclavicular ligament,
  clavicle will rotate posteriorly after 90º
  causing a concurrent upward rotation of AC joint
• Throughout elevation the clavicle also retracts
  at the SC joint approximately 20-25º
• Of the 60º of scapular motion (2 to 1 ratio), 20º
  at AC and 40º at SC joint

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Movements
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Movements
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Movements
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Scapular Winging

• Causes
• Substitution Patterns

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Static Stability of GH

• Mostly passive
• Superior gleno-humeral and coracohumeral
  ligaments
• Passive tension on rotator cuff attachments to
  capsule
• Airtight seal in joint provides a negative
  intrarticular pressure (tears in capsular
  glenoid labrum usually result in less stability)
• EMG activity shows minimal activity by rotator
  cuff but following stroke involving these, GH
  subluxation is very common

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GH Stability
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Static Stability
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Dynamic Stability

• Primarily Deltoid and Rotator Cuff
• Long head of the biceps helps by helping center
  the head of humerus in the glenoid fossa

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Dynamic Stability
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Dynamic Stability
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Muscle Actions

• Upward rotation of the scapula
• SA and Trapezius (Upper and Lower)

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Trapezius
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Trapezius
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Serratus Anterior
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Serratus Anterior
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Upward Rotation Force Couple
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Upward Rotation
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Muscle Actions Elevation Flexion or ABD

• Deltoid
• Initially, from resting position, predominantly
  translatory superiorly, becomes rotatory for
  elevation into range with synergistic effort of
  infraspinatus, t. minor and subscapularis
• Depends on scapular movement to maintain length
  tension relationship
• Activity peaks at 90-120º of ABD
• Peak at flexion near the end of range
• Middle deltoid prime mover for ABD, anterior for
  flexion

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Deltoid
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Clavicular Head of P. Major
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Elevation

• Supraspinatus
• Active throughout ABD ROM, especially 1st 60º
• Can produce motion even when Deltoid weakened but
  motion will have decreased over-all strength
• Secondary function compresses GH joint

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Supraspinatus
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Supraspinatus
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Supraspinatus
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Rotator Cuff
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Rotator Cuff
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Blood Supply to Rotator CuffNote Supraspinatus
has notoriously poor b.s.
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Other Muscles

• Infraspinatus, teres minor, subscapularis
• Active throughout ROM, more in ABD than flexion
• Very active initially, sliding head of humerus
  down (accessory motion)
• Very active late producing external rotation
  for head of humerus to clear acromion

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Muscles actions and roles

• Retraction (ADD with downward rotation)
  necessary with return from elevated position
• Normal return from active elevation will be
  passive or performed by gravity
• Eccentric role of elevators
• Rhomboids, lower trap. Increase as resistance
  increases
• Against heavier resistance
• L. dorsi
• T. major

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Rhomboids, Lower Trap., L. Dorsi, T. Major
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Rhomboids
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Trapezius, L. Dorsi
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Muscles actions and roles

• The role of the biceps brachii in shoulder
  motions
• Tendon of the long head
• Relationship to joint capsule
• Bicipital groove tenosynovium, transverse
  humeral ligament
• Shoulder flexion and abduction
• Possible role in elevation

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Biceps Brachii
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Biceps Brachii
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Common Shoulder Injuries

• Separated Shoulder/AC Degeneration
• Type I Sprain to AC ligament
• Type II Ruptured AC, Sprained Coraco-clavicular
• Type III Rupture to both
• Type IV Post. displaced clavicle complete
  rupture
• Type V inf. displaced clavicle rupture to
  both 3 to 5 X coracoclavicular space
• Type VI complete rupture, clavicle severely
  displaced inferiorly and posteriorly

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Common Injuries

• Dislocated/Subluxed Shoulder
• Trauma
• Nervous system involvement e.g., CVA

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Instability and Impingement

• Primary impingement
• Intrinsic rotator cuff degeneration
• Extrinsic shape of the acromion and
  degeneration of the corcoacromial ligament
• Anterior shoulder pain and dysfunction usually
  with the older patient (40)

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Impingement

• Secondary impingement
• Typically seen in younger (15-35)
• Anterior pain and dysfunction
• Due to muscle dynamics, e.g., muscle imbalance
  and abnormal movement patterns at both GH and
  scapulo-thoracic
• Commonly seen in conjunction with instability of
  either GH or Scapula
• Hypermobile of lax joint does not necessarily
  imply instability

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Impingement

• Secondary (Cont)
• Instability implies the patient is unable to
  control or stabilize a joint during motion or in
  a static position
• Either because the static restraints have been
  have been injured (as seen in anterior
  dislocation with tearing of the capsule and
  labrum) or because the muscles controlling the
  joint are weak or the force couples imbalanced

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Impingement

• Internal impingement
• Found posteriorly mostly in overhead athletes
• Involves contact of of the undersurface of the
  rotator cuff (especially supra and infraspinatus)
  with the posterior glenoid labrum when the arm
  ABD to 90º and externally rotated fully

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Grades of Impingement

• Grade I Pure Impingement with no instability
  (often seen in older patients)
• Grade II Secondary Impingement and instability
  caused by chronic capsular and labral microtrauma
• Grade III Secondary Impingement and instability
  caused by generalized hypermobility of laxity
• Grade IV Primary Instability with no impingement

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Labrum Tears

• Quite common in throwing athletes
• Bankart antero-inferior labrum torn
• Occurs commonly with traumatic anterior
  dislocation
• SLAP superior labrum, anterior and posterior
  detaches from 10 to 2 oclock
• Generally occurs during deceleration

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Labrum
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Common Shoulder Injuries

• Anterior Gleno-Humeral Instability
• Bicipital tenosynovitis
• Rupture of the long head of the biceps