Scapular Orientation and Movement

Introduction to the Shoulder Complex

• The shoulder complex involves the acromioclavicular, sternoclavicular, glenohumeral, and scapulothoracic joints.

Objectives

• Discuss the joints that comprise the shoulder complex.
• Review the structure of the joints of the shoulder complex.
• Discuss the passive and active components of the shoulder complex.
• Describe the kinematics and arthrokinematics of the joints of the shoulder complex.
• Describe the integrated function of the shoulder complex.

The Shoulder Complex

• Four mechanically interrelated articulations make up the shoulder complex.
• The shoulder complex involves the sternum, clavicle, ribs, scapula, and humerus.
• It's designed for mobility.
• Passive structures provide minimal stability.
• Dynamic stability is crucial for the shoulder complex.
• Muscular control maintains stability during active movements.
• Muscle forces primarily secure the shoulder girdle to the thorax.

Joints of the Shoulder Complex

• The shoulder consists of the sternoclavicular (SC) joint.
• The shoulder consists of the acromioclavicular (AC) joint.
• The shoulder consists of the scapulothoracic (ST) "joint".
• The shoulder consists of the glenohumeral (GH) joint.

Sternoclavicular Joint

• The sternoclavicular joint is the only structural attachment between the axial skeleton and the shoulder/upper extremity (UE).
• It's the articulation of the medial clavicle with the manubrium of the sternum and the 1st costal cartilage.
• The sternoclavicular joint is a synovial, saddle joint.
• At rest, the joint space is wedge-shaped and open superiorly.

Osteokinematics of SC Joint

• There are 3 rotational degrees of freedom in the SC joint.
  • Elevation/depression of the clavicle is possible.
  • Protraction/retraction of the clavicle is possible.
  • Anterior/posterior rotation of the clavicle is possible.
  • Long-axis rolling motions of the entire clavicle are possible.
  • These motions are based on the motion of lateral clavicle.
• There are 3 translatory degrees of freedom in the SC joint.
  • They are very small in magnitude in a healthy joint.
• Elevation and depression occur near the frontal plane.
• Protraction and retraction occur near the transverse plane.
• Rotation occurs around the longitudinal axis.
• Elevation ROM: up to 48°.
  • The full range of elevation isn't typically used during functional arm elevation.
• Depression ROM from neutral is less than 15°.
• Protraction ROM is 15°-20°.
• Retraction ROM is ~30°.
• Anterior rotation past neutral is less than 10°.
  • This brings the arm down from overhead/extends the arm behind the back.
• Posterior rotation is up to 50°.
  • This brings the arm over head.

Sternoclavicular Joint Components

• The SC disc acts as a pivot point for the medial end of the clavicle during movements.
  • It transects the joint into 2 cavities.
• The SC disc limits medial translation of clavicle
• It improves joint stability.
• Increasing congruence and absorbing forces transmitted along the clavicle.
• The upper attachment of the sternoclavicular joint is posterosuperior clavicle.
• The lower attachment for the sternoclavicular joint is manubrium, 1st costal cartilage, and the joint capsule.

Sternoclavicular Capsule & Ligaments

• The sternoclavicular capsule a relatively strong fibrous capsule.
• It's supported by 3 ligament complexes.
  • Anterior and posterior ligaments
  • Bilaminar costoclavicular ligament
  • Interclavicular ligament
• The thick posterior capsule primarily resists anterior and posterior clavicular translations.
• Anterior and posterior sternoclavicular ligaments reinforce the capsule.
  • They limit anterior and posterior translation of the medial clavicle.
• The costoclavicular ligament is a very strong ligament composed of 2 bundles.
  • They both limit clavicle elevation.
  • The posterior bundle resists medial translation of the clavicle.
  • It serves as the functional axis of rotation.
  • This ligament absorbs and transmits superiorly directed forces applied to the clavicle via the SCM and sternohyoid muscles.
• The interclavicular ligament limits excessive depression of the clavicle.
  • It protects the brachial plexus and subclavian artery.
  • It limits the superior gliding of the medial clavicle on the manubrium.

Arthrokinematics of SC Joint

• During clavicular elevation:
  • The lateral end of the clavicle move superiorly.
  • The medial clavicle surface rolls superiorly and slides inferiorly on the sternum and 1st rib.
• During clavicular depression:
  • The lateral clavicle moves inferiorly.
  • The medial clavicle surface rolls inferiorly and slides superiorly.
• During clavicular retraction:
  • The lateral clavicle moves posteriorly.
  • The medial clavicle rolls and slides posteriorly on the sternum and 1st costal cartilage.
• During clavicular protraction:
  • The lateral clavicle moves anteriorly in the transverse plane.
  • The medial clavicle rolls and slides anteriorly on the sternum and 1st costal cartilage.

Clavicular Rotation

• Clavicular rotation occurs as a spin between the joint surfaces and disc.
• The Clavicle rotates primarily posteriorly from neutral.
• The axis of rotation runs longitudinally through the clavicle, intersecting the SC & AC joints.

Acromioclavicular Joint

• The acromioclavicular joint is the articulation between the lateral clavicle and the acromion of the scapula.
• It is an incongruent plane, synovial joint.
• There are 3 rotational and 3 translational degrees of freedom.
• This joint allows the scapula to move in 3 dimensions during arm movement.
  • It increases upper extremity motion.
  • It positions the glenoid beneath the humeral head.
  • It helps maximize scapula contact with the thorax.
• It assists in force transmission from the upper extremity to the clavicle.
• There is variability in the shape of articular surfaces from flat to concave/convex in the joint.
• The relatively vertical orientation of surfaces makes it susceptible to shearing forces, leading to degenerative effects.
• Initially, this joint is a fibrocartilaginous union between the clavicle and acromion.
  • With upper extremity use over time, joint space develops.
  • It may leave a "meniscal homologue" within the joint.
• The fibrocartilage remnant (disc) varies in size among individuals and between the shoulders of the same individual.

Acromioclavicular Capsule and Ligaments

• The capsule of the AC joint is relatively weak
• It is reinforced by:
  • Superior Acromioclavicular ligament
  • Inferior Acromioclavicular ligament
  • Coracoclavicular ligaments
• The superior acromioclavicular ligament resists anteriorly directed forces applied to the lateral calvicle.
  • It is reinforced by aponeurotic fibers of trapezius and deltoid muscles.
  • It also happens to be stronger than the inferior and lateral joint capsule.
• The coracoclavicular ligament is divided into the:
  • Conoid Ligament: More triangular and vertically oriented.
  • Trapezoid Ligament: Quadrilateral and is oriented more horizontally.
• Plays a role in coupling posterior clavicle rotation and scapula upward rotation during UE elevation.
• The Conoid portion Primarily restrains inferior translation of acromion relative to lateral clavicle.
• The trapezoid portion restrains posterior translation of lateral calvicle, relatice to the acromion.
• Both portions limit upward rotation of the scapula at the AC joint.

Acromioclavicular Joint Kinematics

• The axes of motion are difficult to define due to variability in joint surfaces among individuals.
• Motions occur around axes oriented relative to the plane of the scapula.
  • Internal/external rotation.
  • Anterior/posterior tilting.
  • Upward/downward rotation.

Resting Position of Scapula

• The scapula rests in an internally rotation of 35° to 45° anterior relative to the coronal plane.
• Later view: scapula is anteriorly titled ~10° to 15° from vertical.
• The "longitudinal" axis of the scapula at rest is upwardly rotated 5° - 10° from vertical.
• IR/ER of scapula at AC joint occurs around a nearly vertical axis.
• Ant/post tilting occurs around an oblique "coronal" axis.
• Upward/downward rotation occurs around an oblique "A-P" axis.
• AC motion also influences, and is influenced by, rotation of clavicle.
• Small translations occur at AC joint: anterior/posterior, superior/inferior and medial/lateral.

Motions at the Acromioclavicular Joint

• Internal and External rotation occurs at the AC joint.

  • IR orients glenoid fossa anteromedially.
  • ER orients glenoid fossa posterolaterally.
  • IR & ER help maintain contact of scapula with the curvature of the thorax.
  • Positions the glenoid fossa toward the plane of humeral elevation
    • Maintains the congruency and stability between humeral head & scapula
    • Maximizing function of GH muscles, capsule, and ligaments.

• Anterior and Posterior Tilting occurs at hte AC Joint

  • Occurs around oblique coronal axis
  • Anteriorly the acromion moves forward; the inferior angle moves posteriorly.
  • Posteriorly the acromion moves backward; the inferior angle moves anteriorly.
  • Anterior tilting occurs in combination with scapular elevation.
  • Posterior tilting occurs in combination with scapular depression.

• Upward and Downward Rotation

  • Rotation occurs around and oblique (A-P) axis
  • At downward rotation - the glenoid fossa tilts downward and the inferior angle of the moves medially
  • Isolated passive motion at the AC joint is limited by coracoclavicular ligament. In order to achieve upwards motion the post rotation of the clavicle reduces tension of the coracoclavicular ligament, then allowing upward rotation to occur

Stability of Acromioclavicular Joint

• This is not an inherently stable joint
• Susceptible to trama and degenerative changes as the person ages
• Trauma related accidents are the the most common as a child to the 3rd decade of life, such as falling on the should or part taking in contact sports.
• This can lead to degenerate changes

Scapulothoracic "Joint"

• The scapulothroacic Joint is the anterior surface of the scapula and the thorax
• Unlike other Joints this is not a True Anatomic structure
• As such this structure is Interdependent with AC & SC Joints
• Any movment on the thorax is influenced by its movement at the SC,AC, and and both.
• In order to work it need to be stabilized as listed below - Integretity os the AC & SC Joints - Muscle strenght and control - Dynameic Sterlilization

Scapulothoracic kinematics

• Rotational movements, with includes - upward/downward rotation - Internal/external rotation - Anterior/posterior tilting
  • Scapulothoracic elevation/depression and protraction/retraction are considered translatory motions

Upward/downward rotation

       - The principal motion of the scapula is during active elevation of arm
        - Full upward rotation of scapula requires: and needs the following motions with include,
           - Elevation at sternoclavicular joint
            - Clavicular posterior rotation
             - Upward rotation at the AC joint

Scapulothoracic Joint Elevation and Depression

      - This requires both Scapulothoraic and clavicular movment.

A small Adjustments At AC, are to help with IR,ER, and other anti post tiltting

Scapular protaction and relation

• Full Scapular protraction requires a anteroposterior facing glenoid

Interal & Eternal Rotation

• Internal Rotation is usally caused from the patients Protaction or retraction from the Claviale at at hte SC joint. ~15° of Internal Rotation is normal when eleavting the the arm

• Internal Rotation can cause cause issue if if Exccesvie.

• Anterior and Posterior Tilting

• May couple with rotation of clavicle at SC jt,

• Excessive anterior tilting can result in prominence of that the inferior anfle. -May be caused by poor neuromuscular control, faulty posture, and/or muscle tightness (pec minor)

Muscle Acition at the Scapulothoracic Joint

• There are a lot of muscle and different motions, please see notes for detail list of involvement and different muscles.

Glenohumeral Joint

Aspects on the Gh Joint

• Ball & socket, synovial joint
• 3 rotary & 3 translatory dof
• Articulation b/w humeral head and glenoid fossa Motions of scapula influence GH joint function
• Designed for mobility
• Reduced stability increases susceptibility to instability, injury and degenerative changes

Glenohumeral Joint artitular surfaces

• Glenoid fossa: shallow concavity, and the resting position is tiled upward slightly.
• Orientation of gleniod varies with respect to resting position of scapula; the fossa is not always in a plane perpendicular to a plane of the scapula. - Anteversion glenoid: this is fossal faces slightly and posterior Retroversion: the gleniod fossal faces slightly anterior

Glenohumeral Angles

• Two important angles that need to be taken in consideration Angle of inclination -Formed by an axis through humeral head & neck Angle of torsion -Formed by an axis through the humeral head and neck

Glenohumeral Joint and accerroy Structure

• Glenoid labrum that Surrounds and is attached to glenoid fossa which in turns enhances articular surface - Increases the depth/concavity
  -Resists humeral head translations

• Protects bony edge

• Helps to Minimize GH friction Attachment site for long head of biceps and glenohumeral ligaments

• Large, loose jt capsule, being taut superiorly and loose inferiorly; it tighten and arm arm is fully abducted & externally rotated (close) - It is Reinforced by: - Superior GH ligament - Middle GH ligament - Inferior GH ligament and Coracohumeral ligament

Glenohumeral Joint and Rotatort Cuffs

• Rotator interval capsule it is a
  • Superior GH capsule it also consists of Superior GH,and Coracohumeral ligamen
• it Bridgethe gap b/w supraspinatus and subclavian joint

Superior vs Middle Gh

• Superior GH
• Deep to coracohumeral ligament

Ighlc:

     - Three Components in this
       Anterior & posterior ligament bands
       The Axiillary pouch in between

• IGHLC and fuction the Major role of jt stabilization with abd > 45° or with combined abd + rotation - ABD > 45°, inferior capsule slack is taken up, and resists inferior humeral head translation - With ABD + ER the Anterior band will fan out to provide anterior and it Resists anterior & inferior humeral head translation - With + IR the the Posterior band will help , resist anteriorly on the humeral head

Arch and Bursa

Coracoacromial Arch

A structure which is formed with both the following properties

Osseous

• Coracoid process
• Undersurface of acromion

Connective

• Coracoacromial ligament
• Inferior surface of AC joint

Creates an osteoligamentous " Vault for better Support and support " over the humeral head

Which it in turns help creating a area b/w humeral head and the above arch.

Glenohumeral Kinematics

• Fexion
  -Pure GH flexion is ~ 120° Extension -Pure GH extension is ~ 50° Medial/Lateral Rotation -ROM varies with the postion with the arms position
  • Rotation with arm at side is less than when abducted It has
• ER of humerus is needed for full ABD
• Allows greater tubercle to pass under or behind coracoacromial arch

Position of the Glenohumeral

• the Open pack position of GH joint is @: 50-55° ABD, 30° HADD

Key facts about Scaption

Scaption: abduction in the scapular plane (30° to 45° anterior to the frontal plane) Allows for better due to less capsular restriction in this position as compared to abduction in the frontal plane

Arthrokinematics

• it needs a
• Inferior slide of humeral head for normal ROM to occur
• Arthokinimatic requires these two compnonets with
• Superior roll
• and inferior slid
  • It both are missing this can lead to impringet

Arthrokinematics and Axis

• As the articular surface slides dueing the. a abduction, the axis of rotation of humerus shifts slightly superiorly

During Fexion and extention slide

• When the humeral head the spin in place is largely due. this is because the Rotation with arm at side is less than

  • Flexion: humeral head spins with slight posterior slide
    • Extension: humeral head spins

• Lateral Rotation the humeral head rolls posteriorly & slides anteriorly the inverse effect is true of medial as the humerla head the rolls anteriorly & the humeral headl is sliding posteriorly

Sterlized

• Downward pull of gravity is opposed by passive tension in rotator interval capsule Resultant force the stabilizes humeral head on glenoid fossa factors assisting in holding humeral head in place at rest: Joint capsule creates a negative intra-articular pressure Slight upward tilt of the glenoid fossa for better aligmnent

GH JOINT and stablized

• Dynamic stabilization is often related to: -Force of the prime mover or movers - Force of gravity - Force of the muscular stabilizers
• Articular surface geometry
  • Passive capsuloligamentous forces, is also the Force of friction within joint - Plus the Joint reaction for that

In cases with Large translatory component small rotary component, this is

• Because Isolated contraction of deltoid would cause more superior translation than rotation of humerus, thus it need to take help in this case

Stablizling Rotatyor cutts

Major contribution to dynamic stability of GH jt Net force will help, the some rotation of humerus, & compresses humeral head into glenoid

and inferiorly directed line

offset the superirior and give a Creates force couple to produce rotation of humeral head with minimal translation

• It nees a Supraspinatus Line of pull to be not offsetting superior translation Relatively large MA allows it to fully ABD - which also with thehelp of Gravity acts as stabilizing synergist the- It Offsets small upward translatory pull muscle

And Finnal there is Force Couple

Of different structure Supraspinatus, Deltoid Subscapularis help to make Slide

Roll Infraspinatus and the Teres minor Abduction - in the glenhumermus portion In short the it, Appears to center the humeral head in fossa & reduce Vertical and anterior translations of humeral head for Dynamic Stabilization of Glenohumeral Joint

Flexion has the

Deltoid (anterior),with Pectoralis major clavicular area and of course to support the Biceps brachii Coracobrachialis In the end, Extension needs

Deltoid posterior portion and to assist Latissimus dorsi Biceps brachii Also to consider these areas Pectoralis major is stermal head Teres major

In order to get Abduction, it needs Supraspinatus

The and to support the and to deltoid which is mostly the middel protion

In order to get Adduction, it needs Pectoralis major With also all sides in the Latissimus dorsi, Teres and its Coracobrachialis

If you need rotation

for Medial (Internal) Rotation Pectoralis major, the Subscapularis Teres

with additionl support with , Latissimus and the Deltoid (anterior)

If you want for Lateral Rotation It it to be Infraspinatus but the Teres minor And with Deltoid and its posterior

Integrated Function of the Shoulder Complex

• To achieve we need ST & GH Function Upward rotation of scapula on thorax contributes 50-60° of motion during shoulder elevation with support and the GH + ST motion creates total arc of ~180° for shoulder complex ABD & flexion, where The 2 segments move together we call this the.

• Scapulohumeral rhythm The "setting phase," is around ~30° of elevation

• the Overall ratio of 2° of GH the 1° of ST

The

the Scapular Force couples

• Trapezium and Serratus anterior and other will the assist in a

  • Upward Rotation

• Pectoralis minor -levator and other for a

• Levator Scapula portion

A COUPLE OF COUPLED

the Scapulothoracic the Joint

Coupled Motions with Glenohumeral Flexion

• Scapulothoracic - Requires: - Upward is Rotation
• And a Posterior tilting
• And Internal, the Rotaation initially, followed by external rotation in higher ranges of flexion

Sternoclavicular joint needs the

• It also Elevations along with the Posterior and then you Protraction

  - While Acromioclavicular Needs and does
  

• the Upward

• rotation and is able to support it withHorizontal along the other saggital portion.

• Reverse for extension*

Coupled Motions are with Glenohumeral and Abduction

and Coupled the Motions and need help from Glenohumeral

for with Medial Rotation

Lateral Rotation

with SCapultorica and then you Retraction with Sternoclavicular , also need , to assist, and its with Retraction

In the help of it's it rotation for protraction and it also the has Sternoclavicular with motion - it

And of with protaction, the it need support from

If their is a Questions -Please see Notes

This quiz covers scapular orientation and movement at the acromioclavicular (AC) joint. It includes questions on scapular rotation, tilting, and their impact on glenoid fossa orientation. The quiz also addresses factors limiting scapular movement and clinical implications of restrictions.