Shoulder Complex Arthrology

Shoulder Complex Arthrology

• The shoulder girdle is composed of 4 joints
• The Sternoclavicular joint (SCJ)
• The Acromioclavicular joint (ACJ)
• The Glenohumeral joint (GHJ)
• The Scapulothoracic joint (STJ)
• Movement at the STJ is the result of movement occurring at both the ACJ and SCJ

Scapulothoracic Joint Movements

• Elevation (translation)
• Depression (translation)
• Protraction (translation)
• Retraction (translation)
• Upward rotation
• Downward rotation

Sternoclavicular Joint Anatomy

• The sternoclavicular joint (SCJ) involves complex articulation
• This articulation occurs between the medial end of the clavicle
• As well as the clavicular facet on the sternum
• And the costal cartilage of the 1st rib
• The articular surface of the SCJ is saddle-shaped
• The clavicle is convex along its longitudinal diameter
• The clavicle is concave along its transverse diameter
• The sternum is concave along its longitudinal diameter
• The sternum is convex along its transverse diameter

Connective Tissue of the SCJ

• The SCJ capsule and articular disc
• The SCJ ligaments: interclavicular ligament; anterior/posterior SC ligaments; costoclavicular ligament, which limits all motions except depression
• SCJ muscles: sternocleidomastoid stabilizes the joint anteriorly
• Sternothyroid and sternohyoid stabilize the joint posteriorly
• The subcalvius stabilizes the joint inferiorly

SCJ Osteokinematics

• The SCJ allows for Elevation/depression
• The SCJ allows for Protraction/retraction
• The SCJ Osteokinematics allow for Rotation

SCJ Elevation/Depression

• The SCJ Elevation/Depression occurs around an anterior-posterior axis of rotation
• Max elevation measures 45°, with Max depression at 10°
• Clavicle elevation/depression is associated with scapula motion
• Arthrokinematics of elevation and depression occur along SCJ longitudinal diameter

SCJ Protraction/Retraction

• SCJ Protraction and Retraction occurs around a vertical axis of rotation with 15-30° both directions
• These motions are associated with similar protraction/retraction of the scapula
• Arthrokinematics protraction and retraction occurs along the SCJ transverse diameter

SCJ Longitudinal Rotation

• Longitudinal Rotation occurs around the longitudinal axis of the bone
• Rotation is posterior during shoulder flexion and abduction
• Max posterior rotation measures 40-50°
• Arthrokinematics involves a spin of the head of the clavicle on the disc

ACJ General Features

• The ACJ's lateral end of clavicle
• The acromion of the scapula
• The disc present in the ACJ
• The ACJ is a plane joint with no roll-and-slide arthrokinematics

Connective Tissue of the ACJ

• The ACJ has a capsule and articular disc
• The ACJ has ligaments including superior and inferior AC ligaments along with the coracoclavicular ligament
• ACJ muscles: deltoid and upper trapezius

ACJ Kinematics

• The ACJ allows subtle movements of the scapula allowing max mobility of the scapulothoracic joint
• Scapula at the ACJ has 3 degrees of freedom
• Upward and downward rotation is primary
• Horizontal and Sagittal plane adjustments occur

ACJ Upward/Downward Rotation

• Upward rotation of the scapula at the ACJ occurs as the scapula swings upward and outward in relation to the lateral edge of the clavicle
• This provides an extensive component of overall upward rotation at the scapulothoracic joint

ACJ Horizontal/Sagittal Plane Adjustments

• Horizontal plane adjustment: internal/external rotation around a vertical axis, medial border scapula pivot away/toward post surface of thorax
• Sagittal plane adjustments (ant/post tilt): Med-lat axis, inferior angle pivots away/toward post surface of thorax
• Enhances Quality/quantity movement at STJ

Scapulothoracic Joint Kinematics

• Movements between the scapula and thorax result from cooperation between ACJ and SCJ
  • Elevation and depression
  • Protraction and retraction
  • Upward and downward rotation

Scapulothoracic Joint Elevation/Depression

• Composite SC/AC joint rotations
  • STJ Elevation
    • Elevation of clavicle at SCJ
    • Downward rotation of scapula at ACJ (scapula vertical)
    • Additional adj. ant tilt (Sagittal plane) - flush
  • STJ Depression
    • Depression of clavicle at SCJ
    • Upward rotation scapula ACJ
    • Additional adj. post tilt (Sagittal plane) - flush

Scapulothoracic Joint Protraction and Retraction

• Summation horizontal plane rotations at SCJ/ACJ is required
  • STJ Protraction:
    • Protraction of clavicle at SCJ
    • Internal rotation of scapula at ACJ via horizontal plane adjustment
  • STJ Retraction:
    • Retraction of clavicle at SCJ
    • External rotation of scapula at ACJ via horizontal rotation adjustment

Scapulothoracic Joint Upward and Downward Rotation

• Composite SC/AC joint rotations
  • Upward rotation (Total of 60°)
    • Clavicular elevation at SCJ
    • Scapular upward rotation at ACJ
  • Downward rotation
    • Clavicular depression at SCJ
    • Scapular downward rotation at ACJ

Glenohumeral Joint

• The GHJ has a convex humeral head
• The GHJ has a concave glenoid fossa

GHJ Connective Tissue

• Loose fit of GHJ facilitates extensive mobility
• Bony congruency is inadequate for stability
• Rotator cuff muscles (SITS)
• GHJ capsular ligaments being superior, middle, and inferior (ant, post, inf)
• Coracohumeral ligament
• Long head of the biceps
• Glenoid labrum

Coracoacromial Arch

• Composed of the Coracoacromial ligament and acromion
• Forms the roof of the GHJ
• Forms the Subacromial space -Contains the supraspinatus, subacromial bursa, and LH biceps
• Contains a bursa to decrease friction.

Static Stability of GHJ

• Passive mechanism: two force vectors
  • Superior capsular structures
  • Gravity
• Resultant force vector: compressive locking force/stability
• Glenoid position.
• Active mechanism:
  • Primarily Rotator cuff
  • Overall force is horizontal/compression

GHJ Kinematics

• The GHJ has 3 degrees of freedom
  • Flexion/extension (med-lat axis)
  • Abduction/adduction (ant-pos)
  • Internal/external rotation (vertical axis)
• Often 4th motion defined by horizontal ADD/ABD
• Motion at the GHJ is associated with motion at the SCJ, ACJ, and STJ

GHJ Abduction and Adduction

• GHJ AB is 120°
• Motion is along longitudinal diameter
• Arthrokinematics abduction
  • Convex humeral head rolls superior
  • Slides inferior
• Adduction is the opposite

GHJ Flexion and Extension

• Motion along the Sagittal plane and a med-lateral axis
  • Involves spinning of the humeral head
  • No roll/slide -Involves motion across the plane of the articular surface
  • Slight ant translation at extreme flex
  • 120° flex GHJ

GHJ Internal and External Rotation

• Horizontal plane, vertical axis, transverse diameter
  • ER:
    • Humeral head rolls posterior
    • Slides anterior
  • IR:
    • Humeral head rolls anterior
    • Slides posterior
  • Occurs with Spin at 90°ABD

Summary GHJ Arthokinematics

• AB/AD: Frontal plane, antoposterior axis, roll and slide along longitudinal diameter
• IR/ER: Horizontal plane, vertical axis, roll and slide along transverse diameter
• Flexion/extension: Sagittal plane, med-lateral axis, spin between humeral head and glenoid fossa, across the plane of articular surface, and with IR/ER in 90° ABD

Overall Kinematics of Shoulder Abduction

• Six kinematic principles
  • Principle 1: Scapulohumeral rhythm
    • GHJ abduction occurs with scapular upward rotation at the STJ
    • 2:1 ratio exists (Inman)
    • For every 3° shoulder AB, 2° GHJ Abd, and 1° STJ upward rotation
    • Total 180°; 120° GHJ Abd, 60° STJ up rot
  • Principle 2: 60° upward rotation of the scapula during full shoulder Abd is a result of simultaneous SCJ elevation and ACJ upward rotation
    • Precise angle reported varies, Inman: ~30°SCJ
  • Principle 3: The clavicle retracts at the SCJ during full shoulder abduction (~20°)
    • Places scapula in the plane of arm elevation
  • Principle 4: Upwardly rotating scapula (ACJ) posteriorly tilts (~20°) and, less consistently, externally rotates slightly (~5°) during full shoulder abduction
    • Flushes scapula with thorax, orient glenoid fossa in plane of arm elevation, prevents subacromial impingement
  • Principle 5: Clavicle rotates posteriorly (SCJ) around its own long axis (20-35°)
    • Upward rotation of scapula at ACJ draws Coracoclavicular lig. taut, post. rotates clavicle
  • Principle 6: GH joint externally rotates during shoulder abduction (~25-50°) greater tubercle pass posterior to the acromion process, prevent jamming against subacromial contents
• Frontal and Scapular planes- AB in frontal plane requires greater ER to complete the movement
• AB in the scapular plane does not need ER (or less ER) to complete movement involving the greater tubercle under the high point of the Coracoacromial arch

Elevators of the ST Joint

• Upper trapezius
• Levator scapulae
• Rhomboid major and minor to a lesser extent

Depressors of the ST Joint

• Lower trapezius
• Latissimus dorsi (indirect)
• Pectoralis minor
• Subclavius (indirect) – small role

Protractors of the ST joint

• Serratus anterior (Prime)
• Pectoralis minor

Retractors of the ST Joint

• Middle trapezius
• Lower trapezius
• Rhomboid minor
• Rhomboid major

Muscles that Elevate the Arm - 3 Groups

• Muscles that elevate the humerus at GHJ
• Scapular muscles that control upward rotation of STJ
• Rotator cuff muscles that control dynamic stability and the arthrokinematics of the GHJ

Muscles that elevate the arm at GHJ

• AB GHJ: Anterior deltoid, Middle deltoid and Supraspinatus muscles
• Flex GHJ: Ant. Deltoid, Coracobrachialis and Biceps brachii

Upward rotators at STJ

• Upward rotation produced by a force couple: upper trapezius, lower trapezius, and lower serratus anterior
• Retractors neutralize the protraction effect of the SA
  • Retractors dominate

Upward rotators at STJ (Force Couples)

• Adjustments can be made via force couples
• Posterior tilt occurs via the lower trap and serratus anterior
• External rotation occurs via the middle trap and serratus anterior

Function of Rotator Cuff during Elevation

• Supraspinatus rolls and compress the humeral head into glenoid
• Subscapularis, infraspinatus, and teres minor inferior glide of the humeral head
• Infraspinatus and teres minor rotates the humeral head externally

Muscles that Adduct & Extend GHJ

• Latissimus, Sternocostal head pec major, Teres major, L.H. triceps, Post deltoid, Infraspinatus, Teres minor
• Scapular stabilization by Rhomboids during ADD/EXT

Internal Rotator Muscles GHJ

• Subscapularis
• Pectoralis major
• Latissimus D
• Teres major
• Anterior deltoid

External Rotator Muscles GHJ

• Infraspinatus
• Teres minor
• Posterior deltoid
• Scapula stabilized by MT