The Shoulder Complex

Introduction to the Shoulder Complex

• Four joints comprise the shoulder complex:
  • Sternoclavicular (SC)
  • Acromioclavicular (AC)
  • Scapulothoracic (ST)
  • Glenohumeral (GH)

Objectives

• Discussion of the joints that comprise the shoulder complex
• Review of the structure of the joints within the shoulder complex
• Explanation of the passive and active components of the shoulder complex
• Description of the kinematics & arthrokinematics of the different shoulder joints
• Explanation the integrated function of the shoulder complex

The Shoulder Complex

• Four mechanically interrelated articulations are a part of the shoulder complex.
• This includes the sternum, clavicle, ribs, scapula, & humerus
• Shoulder complex is designed for mobility
• The passive structures don't provide major stability.
• The shoulder depends on dynamic stability.
• Muscular control of the shoulder complex provides stability during active movements.
• Muscle forces are a primary mechanism that secure the shoulder girdle to the thorax.

Joints of the Shoulder Complex

• Complex includes 4 Joints
  • Sternoclavicular (SC) Joint
  • Acromioclavicular (AC) Joint
  • Scapulothoracic (ST) "Joint"
  • Glenohumeral (GH) Joint

Sternoclavicular Joint

• The SC joint provides the only structural attachment b/w the axial skeleton & the shoulder/UE.
• This constitutes an articulation of the medial clavicle with the manubrium of sternum & 1st costal cartilage.
• It is classified as a synovial, saddle joint
• At rest, the SC joint space is wedge-shaped & open superiorly

Osteokinematics of SC Joint

• There are 3 rotational degrees of freedom (dof)
• Elevation/depression of clavicle
• Protraction/retraction of clavicle
• Anterior/posterior rotation of clavicle
  • Motion of the lateral clavicle is the basis of these movements.
• Long-axis rolling motions of entire clavicle
• There are 3 translatory degrees of freedom in in the SC joint, but they are very small in magnitude in a healthy shoulder
• Elevation & depression occur near frontal plane.
• Protraction & retraction occur near transverse plane.
• Rotation occurs around longitudinal axis
• Elevation ROM goes up to 48°.
• Full range of elevation is not typically used functionally.
• Depression ROM goes from neutral: < 15°.
• Protraction ROM is 15° - 20°.
• Retraction ROM is ~ 30°.
• Anterior rotation past neutral is < 10°.
• While posterior rotation is up to 50°.

Sternoclavicular Joint: SC Disc

• The SC disc acts as a pivot point for medial end of clavicle during movements.
• The SC disc transects the joint into 2 cavities and limit medial translation of clavicle
• Improves joint stability.
• Increases congruence & absorbs forces transmitted along clavicle
• Upper attachment: posterosuperior clavicle
• Lower attachment: manubrium, 1st costal cartilage, & jt capsule

Sternoclavicular Capsule & Ligaments

• Relatively strong fibrous capsule that is supported by 3 ligament complexes:
• Anterior & posterior sternoclavicular ligaments
• Bilaminar costoclavicular ligament
• Interclavicular ligament
• Thick posterior capsule is the primary restraint to both anterior & posterior clavicular translations.
• Anterior & posterior sternoclavicular ligaments
• Reinforce the capsule
• Limit anterior & posterior translation of medial clavicle
• Costoclavicular ligament
• A very strong ligament composed of 2 bundles.
• The ligament limits clavicle elevation
• The posterior bundle also resists medial translation of clavicle.
• Serves as functional axis of rotation
• Absorbs & transmits superiorly directed forces applied to clavicle via SCM & sternohyoid muscles.
• Interclavicular ligament
• Limits excessive depression of clavicle
• Protects brachial plexus & subclavian artery
• Limits superior gliding of medial clavicle on manubrium

Arthrokinematics of SC Joint

• During clavicular elevation the lateral end of clavicle moves superiorly.
• The medial clavicle surface rolls superiorly & slides inferiorly on sternum and 1st rib.
• During clavicular depression, the lateral clavicle moves inferiorly and the medial clavicle surface rolls inferiorly & slides superiorly.
• During Clavicular retraction the lateral clavicle moves posteriorly while the medial clavicle rolls & slides posteriorly on sternum and 1st costal cartilage.
• During clavicular protraction, the lateral clavicle moves anteriorly in the transverse plane while the medial clavicle rolls & slides anteriorly on sternum and 1st costal cartilage.
• Clavicular Rotation
• Occurs as a spin between the joint surfaces & disc.
• The clavicle rotates primarily posteriorly from neutral

Acromioclavicular Joint

• Articulation between the lateral clavicle & acromion of scapula.
• Its an incongruent plane, synovial joint with 3 rotational & 3 translational dof.
• Functions:
• allows scapula to move in 3 dimensions during arm movement.
• increases UE motion. Positions glenoid beneath humeral head.
• helps maximize scapula contact with thorax.

AC Function cont.

• Assists in force transmission from UE to clavicle.
• Articular surfaces variability are have shapes that are flat to concave/convex
• Relatively vertical orientation of jt surfaces makes it more susceptible to shearing forces causing degenerative effects.
• Initially, fibrocartilaginous union between the clavicle & acromion
• Joint space develops with use over time
• May leave a “meniscal homologue" within the joint.
• Fibrocartilage remnant (disc) varies in size among individuals and between the shoulders of same individual.

Acromioclavicular Capsule and Ligaments

• Capsule of the AC joint is relatively weak but reinforced by:
• Superior acromioclavicular ligament
• Inferior acromioclavicular ligament
• Coracoclavicular ligaments
• Superior acromioclavicular ligament:
• Resists anteriorly directed forces applied to lateral clavicle
• Reinforced by aponeurotic fibers of trapezius & deltoid muscles
• Stronger than inferior capsule and ligament
• Coracoclavicular ligament: Divided into:
• Conoid ligament
• Triangular & vertically oriented
• Trapezoid ligament
• Quadrilateral is oriented more horizontally.
• Conoid portion is the primary restraint to inferior translation of acromion relative to lateral clavicle.
• Trapezoid portion is a restraint to posterior translations of lateral clavicle relative to acromion
• Both portions limit upward rotation of the scapula at the AC joint
• This is because AC plays a role in coupling posterior clavicle rotation & scapula upward rotation during UE elevation.

Acromioclavicular Joint Kinematics

• Axes of motion are difficult to define because of the variability in jt surfaces among individuals.
• Motions occur around axes oriented relative to plane of the scapula
• Internal/external rotation
• Anterior/posterior tilting
• Upward/downward rotation
• The scapula has a specific resting position with internal rotation 35° - 45° anterior to coronal plane and anteriorly tilted ~10° - 15° from vertical.
• Longitudinal axis of the scapula at rest is upwardly rotated 5° - 10° from vertical
• AC motion also influences, and is influenced by rotation of clavicle
• Small translations also occur at the AC
  • Anterior/posterior
  • Superior/inferior
  • Medial/lateral

Motions at the Acromioclavicular Joint

• Internal & External Rotation
• When the IR orients glenoid fossa anteromedially / ER orients glenoid fossa posterolaterally They help maintain contact of scapula with curvature of thorax and Positions glenoid fossa toward plane of humeral elevation
• This maintains congruency & stability between humeral head & scapula and maximizes function of GH muscles, capsule, & ligaments

Motions at the AC Joint cont.

• Anterior and Posterior Tilting at AC Joint
• Occur around oblique "coronal" axis
• The Acromion moves forward & inferior angle moves posteriorly during anterior tilting.
• Acromion moves backward & inferior angle moves anteriorly during posterior tilting
• Anterior tilting occurs in combination with scapular elevation while posterior tilting occurs in combination with scapular depression
• Upward & Downward Rotation
  • Occurs around oblique “A-P” axis where the Glenoid fossa tilts upward & inferior angle moves laterally during upward rotation.
• Glenoid fossa tilts downward & inferior angle moves medially during downward rotation
• In isolated passive motion upward/downward rotation at AC jt is limited by coracoclavicular ligament.
• With integrated active movement there is post. rotation of clavicle. Rotation of clavicle reduces tension reducing strain in coracoclavicular ligaments → which "opens” the AC joint and allows upward rotation to occur.

AC Joint Stability

• AC Joint isn't an inherently stable joint that is suspectable to trauma & degenerative changes
• Trauma related AC jt dysfunction occurs more commonly in first 3 decades of life.
• Contact sports or a fall on shoulder with the arm adducted
• Degenerative changes are more common later in life

Scapulothoracic Joint

• The joint is formed by the anterior surface of scapula and the thorax and isn't a true anatomic joint
• SC & AC joints are interdependent with scapulothoracic motion.
• Any movement of scapula on thorax must result in movement at AC joint, SC joint, or both.
• Stability related to the integrity of both AC joint & SC joint as well as muscle strength and control with dynamic stabilzation
• Scapula rests on posterior thorax ~5 cm from midline between 2nd and 7th ribs.
  • There is significant variability in scapular rest position, even among healthy subjects.
• When properly positioned:
  • Internally rotated 35° - 45°
  • Anteriorly tilted 10° - 15°
  • Upwardly rotated 5° - 10°

Scapulothoracic Kinematics

• Rotational movements including upward/downward and internal/external rotation plus anterior/posterior tilting
• Scapulothoracic elevation/depression & protraction/retraction considered primarily translatory motions.
• Upward Rotation: scapula principal motion during active elevation of arm where Full rotation of scapula during requires:
• Elevation at sternoclavicular joint
• Clavicular posterior rotation
• Upward rotation at the AC joint
• Clavicular elevation and subsequent depression, small adjustments should be present at AC joint.

Scapulothoracic Kinematics Cont.

• Protraction of the clavicle with internal rotation at the AC joint results during scapular protraction
• Retraction of the clavicle with external rotation at the AC joint results during scapular retraction
  • Full scapular protraction results in an anteriorly facing glenoid.
• Internal rotation at about ~ 15° occurs at AC jt with normal elevation of the arm.
  • Excessive IR of scapula may indicate pathology or poor neuromuscular control of the scapulothoracic muscles (esp the serratus anterior)

Scapulothoracic Kinematics Cont.2

• The may couple rotation of clavicle at SC and tilting at the AC
• Excessive anterior tilting can result in prominence of inferior angle of the scapula and the potential for poor muscle control, as well as faulty posture
• Key Actions
  • Muscles responsible for protraction: Serratus anterior + Pectoralis major and minor -Key muscles responsible for retraction Middle trapezius + Rhomboids
  • Scapular elevation: Upper trapezius + Levator scapulae + Rhomboids
  • Muscles that perform Scapular Depression Lower trapezius + Latissimus dorsi + Pectoralis minor -Scapular Upward Rotation: Upper trapezius + Serratus anterior and Lower trapezius
• Key muscles responsible for Scapular Downward Rotation Rhomboids + Latissimus dorsi = Levator scapulae + Pectoralis minor

Glenohumeral Joint

• It is a ball & socket, synovial joint with 3 rotary & 3 translatory dof that occurs between head and glenoid fossa of Humerus
• Motions of scapula influence GH joint function as it is designed for mobility but it is not the most stable and easily injured
• Reduced stability increases susceptibility to instability, injury and degenerative changes

GH Articular Surfaces

• Glenoid fossa has shallow concavity
• Orientation of glenoid varies with respect to resting position of scapula, this tilting effect may create variations in Glenoid Fossa positions
• Anteversion with glenoid fossa faces slightly anterior with respect to plane of scapula
• Retroversion with glenoid fossa faces slightly posterior
• Most commonly the glenoid is in slight retroversion within 6-7 degrees
• Humeral head Forms 1/3 to 1/2 of a sphere and has more surface are than gleniod

GH Articulations in Depth

• Angle of inclination = 130° - 150° degree of variation between the humeral head & the axial column
• Form axis from head to neck then through to axial column for the humeral shaft
• Angle of torsion = 30° formed through humeral head and neck to an axiis that exist through the humeral condyles

Angle of Torsion

• Normal state of glenohumeeral joint: angle has slightly retroverted angle of humeral torsion
• centers humeral head to glenoid fossa when scapula resting arm set at side
• With high amounts of Retroversion in the joint, it can alter position of humerus head with possibility of predisposing to injuries

Glenohumeral: Accessory Structures ( glenoid labrum)

• Accessory Structures of Glenohumeral is the glenoid labrum
• Surrounds and is attached to gleniod fossi -> enhancement and surface articulation
• Protects bony edge and resist head translation minimizing friction and contact
• The joint contains Attachment to the along the long head of the biceps muscle/g lenohumeral ligmanets

Glenohumeral Capsule & Ligaments

• Largely composed of loose capsule that rests comfortably as rest
• Taut of loose capusle tightens under the act of of abduction & or extreme rotation
• Support Structutres
  • Enhanced Through Support gh Ligaments with coracohuermal capusle
• Important Function
• Joint Capusele wta 4-5 pounds of a Negative Intra action to keep shoulder stabilized

Glenohumeral Joint: the Rottaor Internval

• Encacapsualted By ligaments of the coraccoaromial suports
• Comprised of: Superior GH capusles
• Has brudges within the supasipatus ,and supscapualaris
• Key in shoulder Stabilizations

GH Key Ligaments

• The three Superior gh and thickened with high jts is
• Superior GH :Runs from labryum to the neck of umerus but deep to caracolumus
  • It Supports the structure and limits the translation of humeral where the muscles act against these MIddle ah has superior an oblique attachment from laborium to proximal humor
• Supports the arm and Limits Abd to 60 degrees Inferior complex 3 components = Anterior band with Axiialary for the position Variability

GH LC Function

• Majoir role of jt with stabzations from Adb 45 degrees = inferior capuscle Slack as it is the abd and the head translation

• It has 3 components

  . Anterior and Psoterior band to give abiltity and resist to inferior trnslations Anterioir band can also lead to jt stability resistiing anterior and inferiroi Psterior band can do oppisite whch cuses reitsing inferior and posterior humeral translations

Key GH Ligaments

• Arches that suport GH Form Base of the corachoamail and surface that cover Ac joint
• create volues called osteoligamentous to support joint and act a vault that sit over head of hummerus to leave area called subcromal space

Subacromial space

• Is Suprahumeral that Contains
  • Subacromial busra
• Has major rotator cuff tendoings and long Head of biceps Tendo
• Measurement : the health of the GH at the acrrominahumer interval on X-Rays is 10mm with at side and elevates to 5.5 cm with arm
• Glenohumeral Kine
• Long axis (medial/lateral rotation) -Coronal axis (flexion/extension ) -A-P axis (abduction/adduction )
• Open pack position of GH joint during with
• 50-55° ABD AND 30 HADD

GH Kine

Flexion Extension: pure flexion is about 120 degrees, while extention is 50 Media and lateral rotations various positions from arms at side v/s abduction - ER of hummerus needed for ABD to all greater Tubercle to corachalial - Scaptions

• 35 mm and 45 on frontal plant

• GH arthokinematics and Abd motion Abduction Needs Head slide infereioiorl to full range of mmovemt and can have superior roll with sliding for humeral head IF infireeror slide doesn't not occur ,head has high level foimpgmenetr under coal acromial arch

. Axis of the arituclla surface slides downward with movement at humeral shfit superious Spining is preodminatr during flexiona dn extendion on the axis

With laterl rotations head will postieroloraly or slighlty anterior depending on interan rotation with support foorsce to slide

Stabilization

Important to note that all jt need equal force at equilibrium for a balanced level of stability Downwards force in joint opposed with passive and active tension Thes factor include the a negative intra pressure with a tilt on joint

Dynamic Stabilization of the Glenehumeral Joint

Forces of Gravity Force of primary movers Muscler stabiization Surfac e geometry at joints Passive capulse and resistance between the jt Forces like frictions and reactions Deltoid

GH Function

The rotation cuff contribute the stabiilization to the dynamics through net force ,it also support at force couples

ITS MUSCLES: deltoid creates rotation of the head with support from the inforly directed rotator cuff offsets to stabilize superieror deltoid

THE SUBPRASPINOUS Supports the offset from deltoid, contributes to comprssions as it independently produced fully GH ABD

• It has some effects of translation and works synergistically

Force Couple

The GH joint depends heavily on the balance between the supraspinatus/ infraspinatus forces

• It can influence Slide and Roll, it can effect the
• Hummerus movement pattern in different positions

In Addition

• The Biceos Tendoning as a stabilizer for GH is able tor eductions vertical and horizontal translations of the hummerus to have the stability support.

Muscle Actions

• It important to see balance at :
• Extensiom
• Flexion
• Abduction/ Adduction action
• Rotation

Integrated Function

• Is when the ST adn the GH balance each Other for a set amount with a constant balance
• (the degree of motion within all functions must be equal)
• If ST increase for the GH : It can increase the overall amount ot mivemrnt that balance that shoulder does to compensate for shoulder elevation increase ( with support from scapular muscles and functions in the arm. )
• Force balance includes the functions oif the lower scapula in the trapeziiums to keep all balanced which creates a constant ratio of joint performance of: GH and ST ( 2 degrees of freedom to 1 one at at set phase)

Key Couples of Forece

Levator scapular that supprot trap and rhomboids

• At GH flexion, motions are couples with
  Upward motion
• Posterior sliding Internal rotations/ external rotation
• The above creates key elevators that create protractions

At GH addutuons There is Elevation and retraction within the joint to add more surface between the GH and ST at the rotation level.

While GH does medially and Laterial with PRO traction and contraction as a balanced approach and with a ST approach

An introduction to the shoulder complex and its components, including the joints, structure, and passive and active actions. Review the kinematics & arthrokinematics of the shoulder joints. Discuss the integrated function of the shoulder complex.