Kinesiology of the Shoulder

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Joints of the Scapula (3 True/2 Functional): -Sterno-Clavicular
-Acromioclavicular
-Glenohumeral
-Scapulothoracic
-Coracromial Arch
Function of the Scapula: -To link upper extremity to the trunk
-Dependent arm position
-Control of RTC Muscles
-Provide extensive mobility of arm in space
-Provide stability for elbow and hand skillful or forceful movements
-Mobility and Stability
(Proximal Stability for Distal Mobility)
Dynamic Stability: -When muscles are used for stability
-Lack of inherent bony stability
-Little intrinsic stability to the joint complex due to shape of articulation and bony incongruity
-Muscles, ligaments and other soft tissues maintain joint integrity
-Joint stability is due to Dynamic Muscular Control
Plane of the Scapula: -Orientated approximately 30-45 degrees to the frontal plane due to rib shape
Function of the Plane of Scapula: -Spinal Alignment - proper bony alignment
-Strength - Optimal length-tension relationship for shoulder abductors and rotators (Supraspinatus and Deltoids)
Ideal Alignment of Shoulder: -Superior angle of scapula at T2
-Inferior angle of scapula at T7
-5 to 6 cm between spine and medial scapular border
-Acromion in line with mastoid process
-20 degrees anterior tilt between lateral scapular border and vertical
Angle of Inclination of Humerus: -Frontal Plane
-130 to 150 degree angle created between axis of head and shaft of humerus in frontal plane (135 degrees is ideal)
Angle of Torsion - Retroversion: -Transverse Plane
-Humeral head is rotated 30 degrees posteriorly
-Orients humeral head in scapular plane for articulation with glenoid fossa
-Increases stability
Characteristics of Sternoclavicular Joint: -Bony connection of upper limb to the axial skeleton
-Reciprocally convex/concave
-Stability depends on capsule and ligaments
-Triaxial
Ligaments of Sternoclavicular Joint: -Costoclavicular Ligament
-Posterior Sternoclavicular Ligament
-Anterior Sternoclavicular Ligament
-Interclavicular Ligament
Costo-clavicular Ligament: -Principle stabilizing structure of sterno-clavicular joint
-Secures clavicle to 1st rib
-Limits extremes of all clavicular motion except depression
Axis of Rotation for Costo-clavicular Ligament: -Protraction/Retraction
-Elevation/Depression
Sterno-clavicular Ligament: -Lines superior aspect of joint capsule
-Checks anterior/posterior movement
-Restrains protraction and retraction
Joint Disc of SC Joint: -Absorbs schock and helps prevent dislocation
-Intra-articular disc of fibrocartilage
-Increase acrticulating surface area
-Block medial movement of clavicle
-Distribute forces
SC Osteokinematics (3 types): -Protraction-Retraction
-Elevation-Depression
-Rotation
Protraction/Retraction of SC Joint (Plane, Axis, and Ligament): Transverse plane, vertical axis at Costo-clavicular Ligament
Elevation/Depression of SC Joint (Plane, Axis, and Ligament): Frontal plane, A-P axis at coosto-clavicular ligament
Rotation - Axis: Longitudinal Axis
SC Joint Arthrokinematics: Elevation: Convex clavicular head rolls up (CW, Superiorly) and slides down (Inferiorly) on concavity of the sternum.
IN FRONTAL PLANE, CLAVICLE IS CONVEX
SC Joint Arthrokinematics: Depression: Clavicular head rolls down (CCW, Inferiorly) and slides up (superiorly)
SC Joint Arthrokinematics: Retraction: Concave articular surface of clavicle rolls and slides posteriorly on the convex surface of sternum
SC Joint Arthrokinematics: Protraction: Concave articular surface of clavicle rolls and slides anteriorly on the convex surface of the sternum
AC Joint Features: -Gliding or Plane Synovial Joint
-3 degrees of freedom
AC Joint Supporting Structures: Periarticular Connective Tissue: -Superior and inferior AC Ligaments
-Coracoclavicular Ligament (Conoid, Trapezoid)
-Articular Disc (deteriorates at age 20)
-Superior and inferior AC Ligaments (Reinforce joint capsule, prevent posterior dislocation, limits tipping)
Coracoclavicular Ligaments: Major Stabilizing Structure
-Conoid - limits excessive superior glide
-Trapezoid - Protects against shearing forces
AC Joint Osteokinematics: Primary motion - Upward and downward rotation
Secondary motion - Horizontal plane adjustments (Winging), Sagittal plane movements (Tipping)
AC Joint Osteokinematics: Upward Rotation and Downward Rotation: -Primary Motion at AC Joint
-Glenoid Fossa Tilts Up Or Down
-Closed packed position is full upward rotation
-AP Axis
-1st 30 degrees with axis at base of spine of scapula
-Last 30 degrees with axis at AC joint
AC Joint Osteokinematics: Winging: Horizontal plane movement - vertebral border of scapula moves out around vertical axis at AC Joint
-Occurs with scapular abduction and adduction
-If abd/add were pure translatory movement, only vertebral border of scapula would contact ribs
(SERRATUS ANTERIOR WEAKNESS)
AC Joint Osteokinematics: Tipping: -Sagittal plane tilting of scapula - horizontal axis
-Occurs with scapular elevation and depression
-Inferior angle moves away from thoracic wall
Scapulothoracic Joint: -Not true anatomical joint
-Scapular motion moves glenoid fossa into position where it can provide a stable base for humeral head regardless of arm movement
Movements at SC Joint: -Elevation/Depression
-Abduction/Adduction
-Upward/Downward Rotation
SC Joint: Osteokinematic Movements - Elevation/Depression: -Translation up or down
-2 degree motion - Tipping at AC Joint
SC Joint: Osteokinematic Movements - Abduction/Adduction: -Translates side to side
-2 degree motion - Winging at AC Joint
SC Joint: Osteokinematic Movements - Upward/Downward Rotation: -Up - Glenoid faces superiorly
-Down - Glenoid faces inferiorly
-2 degree motion - rotation at AC Joint
Glenohumeral Joint Characteristics: -Most mobile joint in body
-Humeral Head
-Large, convex-ovoid (slide or roll in opposite directions)
-1/2 sphere
-Head faces medial, superior, posterior (retro)
-Glenoid Fossa
-Surface is 1/4 to 1/3 of humeral head surface
Capsuloligamentous Complex of GH Joint: -Capsule
-Rim of glenoid fossa - anatomical neck or humerus
-Allows extensive mobility
-Axillary Pouch (Inferior Border)
-GH and Coracohumeral Ligaments - Reinforce capsule and serve as major static restraints
-Subscapularis-Anterior capsular reinforcement
-Supraspinatus, Infraspinatus, Teres Minor - Posterior Reinforcement
GH Ligaments: -Lax in normal ROM
-Limit translation and rotation of humeral head on glenoid
-Prevent/Limit Extremes in ROM
Superior Glenohumeral Ligament: -Supraglenoid Tubercle - lesser tuberosity
-Taut with full adduction and posterior and inferior humeral translation
Middle Glenohumeral Ligament: -Labrum - Anatomical Neck
-Anterior restraing to GH joint, resists anterior translation of humerus and extremes of ER
Inferior Glenohumeral Ligament: -Anterior, inferior and glenoid labrum - inferior anatomical neck of humerus
-All fibers are taut with abduction
Coracohumeral Ligament: -Lateral coracoid process to anterior greater tubercle
-Strongest supporting GH ligament
-Taut with extremes of ER, Flexion and Extension
*Primary restraint vs. inferior and posterior translation in the adducted arm
*Counter acts downward pull of gravity on humerus
Primary Static Stability of GH Joint: -Fossa oriented upward
-Combine force of coracohumeral ligament and superior capsule and force of gravity (Compressive force pushing humeral head into fossa)
Secondary Static Stability of GH Joint: -Supraspinatus and posterior deltoid
-Active forces parallel to superior capsule
-Decrease in superior capsule --> muscle weakness, poor posture
Coracoacromial Arch: -Coracoacromial ligament and acromion process
-GH roof - protective
-Subacromial space (Supraspinatus, subacromial bursa, long head of biceps, capsule)
-Poor Mechanics --> Impingment

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