Shoulder Kinematics and Scapular Movement

Internal and External Rotation

• ER: The head rolls posterior and glides anterior
• IR in the opposite way
• Simultaneous glide and roll allows head to roll over a smaller surface

AC and SCC Kinematics

• Only passive movements
• All scapular movement = clavicular movement
• Allow for wider ROM added to glenohumeral motion
• Example: shoulder abduction (total of 180 degrees)
  • -60 degrees lateral of the scapula: 20 degrees Acromioclavicular + 40 degrees Sternoclavicular

AC Joint Stabilizers

• Static:
  • Joint capsule: reinforced by capsular ligaments
  • Ligaments: Conoid and Trapezoid ligaments
  • Articular disc
• Dynamic:
  • Deltoid and upper trapezius muscles

SCC Joint Stabilizers

• Static:
  • Fibrous capsule
  • Ligaments: anterior and posterior sternoclavicular, costoclavicular on each side
  • Articular disc
• Dynamic:
  • Subclavius muscle

Scapulothoracic Joint

• Larger shoulder amplitude thanks to ST
• AC and SCC movement all for ST
• Elevation and depression
  • SCC and AC
  • Scapula follows path of clavicle
• Protraction and retraction
  • Horizontal plane rotations of SCC and AC
  • Scapula follows clavicle path

Upward and Downward Rotation

• Upward rotation
  • Arm raise
  • Sum of SCC elevation and AC upward rotation
• Downward rotation
  • Arms come back
  • Sum of SCC depression and downward rotation AC

KINETICS

Muscular Actions

• Proximal stabilizers
• Distal mobilizers

Global Flexion

• First Stage. 0-30/60.GH
  • Motor muscles: anterior deltoids, Coracobrachialis, Clavicular Pectoralis major
  • Movement limits: Coracohumeral ligament strain
• Second Stage. 30/60-120.STj
  • Upward rotation of the scapula
  • Muscles of the Scapulothoracic Joint
    • Elevators: Upper Trapezius, Levator scapulae, Rhomboids
    • Depressors: Lower Trapezius, Latissimus dorsi, Pectoralis Minor, Subclavius
    • Protractors: Serratus Major
    • Retractors: Middle Trapezius, Rhomboids and lower trapezius

Scapulothoracic Joint Muscles

• Upward rotation of the scapula: Serratus anterior, Upper Trapezius
• Retraction and downward rotation: Rhomboids Stabilizers scapula in ADD and GH extension

Muscles that move in ADD and EXTEND the shoulder

• Major isometric moment of the shoulder
  • Agonists: Latissimus and Pectoralis major
  • Synergistic: Infraspiantus, teres minor and major

Rotator Cuff muscles

• FUNCTIONS:
  1. Dynamic joint stability regulators
  2. Arthrokinematics controllers

Muscles that internally and externally rotate the shoulder

• Internal rotators: Subscapularis, anterior deltoid, Pectoralis major, Latissimus dorsi, and teres major
• External rotators: Infraspiantus, teres minor, and the posterior portion of the posterior deltoid

Global Abduction

• First Stage. 0-90 degrees
  • Motor muscles: Deltoids, especially the middle fasciculus and Supraspinatus
• Second Stage. 90-150
  • Upward rotation of the scapula orienting glenoids
  • Motor muscles: Serratus and Upper trapezius
• Third Stage. 150-180
  • Contralateral tilt of the spine due to contraction of the spinal muscles of the opposite side

Global Adduction

• 30-45
  • When arm is in ABD —> the ADD is made by eccentric contraction of ABD muscles
  • Motor muscles:
    • GHj flex: Pectoralis Major and Anterior deltoid
    • GHj extension: Teres major and minor, Latissimus dorsi
    • STj flex: Serratus anterior
    • STj extension: Rhomboids

External Rotation

• 60-70
  • Motor muscles: Infraspinatus and teres minor
  • The movement of scapular adduction is added by the action of the rhomboids and the middle portion of the Trapezius

Internal Rotation

• 75-85
  • Motor muscles: Teres major, Latissimus dorsi, Subscapularis, Pectoralis Major
  • The protraciton movement of the scapula is added by Serratus Major and Pectoralis Minor action