Introduction to the Shoulder Complex

Introduction to the Shoulder Complex

• The shoulder complex includes the acromioclavicular joint, sternoclavicular joint, glenohumeral joint, and scapulothoracic joint.

Objectives

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

The Shoulder Complex

• The shoulder complex consists of four mechanically interrelated articulations.
• These articulations involve the sternum, clavicle, ribs, scapula, and humerus.
• It is designed for mobility.
• Passive structures do not provide major stability.
• It depends on dynamic stability, and it's muscular control provides stability during active movements.
• Muscle forces are the primary mechanism to secure shoulder girdle to the thorax.

Joints

• The shoulder complex is comprised of the Sternoclavicular (SC) joint, the Acromioclavicular (AC) joint, the Scapulothoracic (ST) "joint", and the Glenohumeral (GH) joint

Sternoclavicular Joint

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

Osteokinematics of SC Joint

• The SC joint has 3 rotational degrees of freedom (dof).
  • Elevation/depression of clavicle
  • Protraction/retraction of clavicle
  • Anterior/posterior rotation of clavicle
  • Long-axis rolling motions of entire clavicle
• The SC Joint has 3 translatory dof.
  • This is very small in magnitude in healthy joints, but based on motion of the lateral clavicle.
• Elevation & depression occur near the frontal plane.
• Protraction & retraction occur near the transverse plane.
• Rotation occurs around longitudinal axis.

Osteokinematics of SC Joint: Clavicular Motions

• Elevation ROM: up to 48°.
  • A full range of elevation in SC Joint is not typically used with functional arm elevation.
• Depression ROM from neutral: < 15°.
• Protraction ROM: 15° - 20°.
• Retraction ROM: ~ 30°.
• Anterior rotation past neutral: < 10°.
• Posterior rotation: up to 50°.

Sternoclavicular Joint: SC disc

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

Sternoclavicular Capsule & Ligaments

• The sternoclavicular capsule is a Relatively strong fibrous capsule.
• It 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 and posterior clavicular translations.
• Anterior & posterior sternoclavicular ligaments reinforce the capsule.
• The Anterior & posterior sternoclavicular ligaments limit anterior & posterior translation of medial clavicle.

Sternoclavicular Capsule & Ligaments: Costoclavicular ligament

• The costoclavicular ligament is very strong composed of 2 bundles.
• Both bundles limit clavicle elevation, and limit the clavicle elevator.
• Serve as functional axis of rotation.
• Absorbs & transmits superiorly directed forces applied to clavicle via SCM & sternohyoid muscles.
• The posterior bundle also resists medial translation of the clavicle.

Sternoclavicular Capsule & Ligaments: Interclavicular ligament

• The interclavicular ligament limits excessive depression of clavicle.
• It also protects the brachial plexus & subclavian artery.
• It limits superior gliding of medial clavicle on manubrium.

Arthrokinematics of SC Joint

• Clavicular elevation:
  • Lateral end of clavicle moves superiorly.
  • Medial clavicle surface rolls superiorly & slides inferiorly on sternum and 1st rib.
• Clavicular depression:
  • Lateral clavicle moves inferiorly.
  • Medial clavicle surface rolls inferiorly & slides superiorly.
• Clavicular retraction:
  • Lateral clavicle moves posteriorly.
  • Medial clavicle rolls & slides posteriorly on sternum and 1st costal cartilage.
• Clavicular protraction
  • Lateral clavicle moves anteriorly in the transverse plane.
  • Medial clavicle rolls & slides anteriorly on sternum and 1st costal cartilage.
• Clavicular rotation
  • Occurs as a spin between the joint surfaces & disc.
  • Clavicle rotates primarily posteriorly from neutral.

Acromioclavicular Joint

• There is articulation between the lateral clavicle and the acromion of scapula.
• The AC joint is an incongruent plane, synovial joint.
• With 3 rotational & 3 translational degrees of freedom.
• Functions of this joint allow the scapula to move in 3 dimensions during arm movement.
• Increases UE motion, positions glenoid beneath humeral head, Helps maximize scapula contact with thorax.
• Assists in force transmission from UE to clavicle. -There is Variability in shape of articular surfaces from flat to concave/convex
• Relatively vertical orientation of jt surfaces make it more susceptible to shearing forces → degenerative effects. -Initially, AC Joint is a fibrocartilaginous union between clavicle & acromion.
• With UE use over time joint space develops, this May leave a “meniscal homologue" w/in the joint.
• Fibrocartilage remnant (disc) varies in size among individuals and between the shoulders of same individual.

Acromioclavicular Capsule and Ligaments

• The Capsule of the AC Joint is relatively weak. -The Acromioclavicular Capsule and Ligament is reinforced by:
  • Superior acromioclavicular ligament, which resists anteriorly directed forces applied to lateral clavicle.
  • Inferior acromioclavicular ligament
  • Coracoclavicular ligaments: The more superior AC ligament is stronger than inferior capsule and ligament.

Acromioclavicular Capsule and Ligaments: Coracoclavicular Ligament

• Coracoclavicular ligament is divided into Conoid ligament, and Trapezoid ligament.
• Conoid ligament
  • More triangular & vertically oriented.
• Trapezoid ligament
• Quadrilateral and oriented more horizontally.
• Conoid portion provides the Primary restraint to inferior translation of acromion relative to lateral clavicle.
• Trapezoid portion restrains to posterior translations of lateral clavicle relative to acromion.
• Both portions limit upward rotation of the scapula at the AC joint.
• Plays a role in coupling posterior clavicle rotation & scapula upward rotation during UE elevation.

Acromioclavicular Joint Kinematics

• Axes of motion are difficult to define due to variability in jt surfaces among individuals.
• Motions occur around axes oriented relative to the plane of the scapula:
  • Internal/external rotation, and Anterior/posterior tilting.
• Upward/downward rotation
• Resting Position of Scapula
  • scapula resting in internally rotated position 35° - 45° anterior to coronal (frontal) plane

Resting Position: Scapula

• The scapula is anteriorly tilted ~10° - 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 influences these factors, and is influenced by, rotation of clavicle.
• Small translations also occur at AC jt
• Anterior/posterior, Superior/inferior, and Medial/lateral.

Motions at the Acromioclavicular Joint

• There is Internal & External Rotation.
• IR orients glenoid fossa anteromedially.
• ER orients glenoid fossa posterolaterally.
• IR & ER help maintain contact of scapula with curvature of thorax.
• Positions glenoid fossa toward plane of humeral elevation.
• Maintains congruency & stability b/w humeral head & scapula.
• Maximizes function of GH muscles, capsule, & ligaments.

The Acromioclavicular Joint: Anterior & Posterior Tiliting

• They occur around an oblique "coronal" axis.
• Anterior tilting:
• Acromion moves forward & inferior angle moves posteriorly.
  • Anterior tilting occurs in combination with scapular elevation.
• Posterior tilting:
• Acromion moves backward & inferior angle moves anteriorly.
  • Posterior tilting occurs in combination with scapular depression.

The Acromioclavicular Joint: Upward & Downward Rotation

• Occurs around the oblique “A-P” axis.
• Upward rotation:
  • The Glenoid fossa tilts upward & the inferior angle moves laterally.
• Downward rotation:
  • The Glenoid fossa tilts downward & the inferior angle moves medially.
  • Isolated passive motion of upward/downward rotation at AC joint is limited by coracoclavicular ligament.
• As the clavicle rotates posteriorly, the Post. rotation of clavicle reduces tension of coracoclavicular ligaments, essentially "opens" the AC joint, allowing upward rotation to occur
• The AC joint is not an inherently stable joint.
• It is susceptible to trauma & degenerative changes:
  • Trauma related AC jt dysfunction more common 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"

• Formed by the anterior surface of scapula and the thorax.
  • This is not a true anatomic joint.
• SC & AC joints are interdependent with scapulothoracic motion.
  • Any movement of the scapula on the thorax must result in movement at AC joint, SC joint, or both.
• Stability is related to the Integrity of the AC joint & SC joint Muscle strength and control, and Dynamic stabilization.
• The Scapula rests on posterior thorax ~5 cm from midline between 2nd – 7th ribs with significant variability in scapular rest position, even among healthy subjects.

Scapulothoracic Kinematics

• Rotational Movements: Upward/downward rotation, Internal/external rotation, and Anterior/posterior tilting.
• Scapulothoracic elevation/depression & protraction/retraction are considered translatory motions.
• Upward rotation is the principal motion of the scapula during active elevation of the arm. Full upward rotation of the scapula requires:
  • Elevation at sternoclavicular joint, Clavicular posterior rotation, and Upward rotation at the AC joint.
• Scapulothoracic elevation is commonly paired with clavicular elevation, and clavicular depression.
• Scapulothoracic elevation are small adjustments at AC jt for IR/ER or ant/post tilting to maintain contact with thorax.
• Full scapular protraction results in an anteriorly facing glenoid ~ 15° of internal rotation occurs at the AC joint with normal elevation of the arm.
• Excessive IR of scapula on thorax causes increased prominence of medial border of scapula (Scapular winging). This May indicate pathology or poor neuromuscular control of the scapulothoracic muscles (esp the serratus anterior)
• Anterior and Posterior Tilting Primarily occur at the AC joint.
  • It May couple with rotation of clavicle at SC jt. Excessive anterior tilting can result in prominence of inferior angle of the scapula.
• Excessive anterior tilting May be caused by poor neuromuscular control, faulty posture, and/or muscle tightness (pec minor)

Muscle Actions on the Scapulothoracic Joint

• Scapular Protraction is caused by the Serratus anterior, the Pectoralis major, and the Pectoralis minor.
• Scapular Retraction is caused by the Middle trapezius, and the Rhomboids.
• Scapular Elevation is caused by the Upper trapezius, the Levator scapulae, and the Rhomboids.
• Scapular Downward Rotation is caused by the Rhomboids, the Latissimus dorsi, the Levator scapulae, and the Pectoralis minor.
• Scapular Upward Rotation is caused by the Upper trapezius, the Serratus anterior, and the Lower trapezius.

Glenohumeral Joint

• This is a Ball & socket, synovial joint with 3 rotary & 3 translatory degrees of freedom.
• There is Articulation between Humeral head and glenoid fossa.
• Motions of scapula influence GH joint function.
• Designed for mobility.
• Reduced stability increases susceptibility to instability, or injury and degenerative changes.
• Glenoid fossa has shallow concavity. Orientation of the glenoid varies with respect to resting position of the scapula Often slightly tilted upward
• Glenoid Fossa is not always in a plane perpendicular to the plane of the scapula: If facing slightly anterior this is known as Anteversion, if facing slightly posterior this is called Retroversion
• 6°-7° Most commonly the glenoid is in slight retroversion .
• Articular surface area of the humeral head is larger than that of the glenoid,. When the arms hang dependently at the side, the articular surfaces of GH joint has little or no contact

Glenohumeral Joint: Humeral Head

• The humeral head forms 1/3 to 1/2 of a sphere
• The angle of inclination is formed by an axis through humeral head & neck in relation to longitudinal axis through the humeral shaft, normally ~130°-150°.
• Angle of torsion is formed by an axis through the humeral head and neck in relation to an axis through the humeral condyles.
• The angle of torsion is normally ~30°.
• Normal angle of humeral torsion is slightly retroverted.
  • This Centers Humeral head on glenoid fossa when Scapula is in resting position and arm is at side.
• Excessive retroversion or anteversion causes Alters position of humeral head in glenoid, May predispose to injury

Glenohumeral Joint: Accessory Structures

• TheGlenoid labrum Surrounds glenoid fossa to enhance articular surface which Enhances depth and concavity of fossa by ~50%
• The Glenoid labrum Resists humeral head translations by Protecting bony edges of fossa, Minimizes GH friction and Dissipating joint contact forces
• Attachment site for long head of biceps and glenohumeral ligaments

Glenohumeral Capsule & Ligaments

• Large, loose joint capsule. -Taut superiorly and loose inferiorly when arm is at rest by the side, Maximally tightens when arm is fully abducted & externally rotated (close-packed position)
• Reinforced by: Superior GH ligament Middle GH ligament Inferior GH ligament Coracohumeral ligament:
• The Rotator interval capsule comprised of: Superior GH capsule ligament Coracohumeral ligament Bridges gap between supraspinatus and subscapularis tendons

Glenohumeral Joint: Superior GH ligament

• The Superior GH ligament is a thickened region within the joint capsule and Runs from superior glenoid labrum to upper neck of humerus deep to coracohumeral ligament with rotator interval capsule structures limiting anterior and inferior translations of humeral head when the arm is at the side -Middle GH ligament: Runs obliquely from superior anterior labrum to anterior proximal humerus, Limits anterior humeral translation with the arm at side & up to 60° of abduction
• Inferior glenohumeral ligament complex consists of 3 components comprised of Anterior & posterior ligament bands and Axillary pouch in between, with position-dependent variability in function.
• IGHLC has a Major role of joint stabilization with abd > 45° or with combined abd + rotation where The ABD > 45°, inferior capsule slack is taken up, and resists inferior humeral head translation.
• With ABD + ER the Anterior band of IGHLC fans out anteriorly to provide anterior joint stability and resists anterior & inferior humeral head translation.
• With ABD + IR Posterior band of IGHLC fans out posteriorly to provide posterior joint stability resists posterior & inferior humeral head translation

The Glenohumeral Joint Ligaments and more

• Coracohumeral ligament Originates at base of coracoid process and is Comprised of 2 bands, one inserts supraspinatus tendon & onto greater tubercle and 2nd band inserts with subscapularis & lesser tubercle forming a tunnel for tendon of the long the Bicep. The limits inferior translation of humeral head in dependent arm position and Resists humeral lateral rotation with the arm adducted
• The Coracoacromial Arch is formed by: Coracoid process, Undersurface of acromion, Coracoacromial ligament, Inferior surface of AC joint to Creata an osteoligamentous vault over the humeral head

The Subacromial Space

• A.k.a suprahumeral space. Consists of:
  • Subacromial bursa (reduces friction with humeral head and tendons), Rotator cuff tendons, and Long head of biceps tendon
  • Measured as acromiohumeral interval on x-rays where. -Healthy individuals have ~10 mm with arm at side and ~5 mm of space with arm elevated overhead

Glenohumeral Kinematics

• Flexion/Extension: Pure GH flexion is ~ 120° and Pure GH extension is ~ 50° Medial/Lateral Rotation: ROM varies with position where rotation with Arm at side is less than when Abducted
• Abduction/Adduction- ER of humerus is needed for full ABD this allows Greater Tubercle to pass under or behind coracoacromial arch :

Open pack position of GH joint is when at 50-55° ABD with 30° HADD/Horizontal Abduction Scaption occurs when Abduction in this scapular plane (30° to 45° anterior to the frontal plane) Often allows for greater ROM due to less capsular restriction in this position as compared to abduction in the frontal plane • Glenohumeral Arthrokinematics

Glenohumeral Arthrokinematics: ABD

• Abduction of GH jt requires an inferior slide of humeral head for normal ROM to occur:
  • Superior roll of humeral head, Inferior slide of humeral head o W/o an inferior slide the Humeral head will impinges on coracoacromial arch o As the articular surface slides inferiorly with
• Abduction, the axis of rotation of humerus shifts slightly superiorly o Flexion & Extension: Humeral head largely spins in place O Flexion: humeral head spins with slight posterior slide O Extension: humeral head spins with slight anterior slide o

Lateral (External) Rotation humeral head Rolls posteriorly And Slides anteriorly Medial (Internal) Rotation Humeral head Rolls anteriorly And Slides posteriorly

• Downward pull of gravity is opposed by passive tension in rotator interval capsule, Restraint force stabilizes humeral head on glenoid fossa:
• Other factors assisting with holding the humeral head at rest is Negative joint capsule intra-articular pressure (a relative vacuum) is made and the glenoid sits with a slight tilt,
• Dynamic stabilization in linked to the force of the prime mover -Muscular stabilizers -Articular surface geometry -Capsuloligamentous forces - Force of gravity - Friction within joint -Joint reaction force isolated for translation over rotation over movement causes a much bigger
• D = action line of all 3 deltoids pulls Fx = large translatory component (cause superior translation) Fy = small rotary component Isolated deltoid contraction more superior translation than rotation of humerus

Dynamic Stabilization of the Glenohumeral Joint

• The Rotator cuff muscles a Major contribution to dynamic stability of GH jt while the next force of ITS some rotation of humerus & compresses humeral head into glenoid

• The Rotor cuff produces this force with Inferior movement while gravity is working against It causes rotation & inferior translation

• Super Spinous does not have a line of pull. Its primary purpose is to aid Joint Compression with and helps it compress due to the fact that with a large relatively large moment arm (MA) Gravity often acts as a stabilizer and helps balance its movement Force to be superior -Supraspinatus helps abduct arm with joint compression helps with small tension is muscle

There is Force couple of GH Joint Deltoid Subscapularis infraspinatus

Glenohumeral Joint Recap

(Questionable significance- it helps control

Muscle Actions at Internal Rotation

• Pectoralis major
• Subscapularis
• Teres major
• Latissimus dorsi
• Deltoid (anterior) joint
• The External rotation
• Infraspinatus
• Teres minor
• Deltoid (posterior) joint The Flexion
• Deltoid (anterior)
• Pectoralis major (clavicular joint
• Coracobrachialis joint Extension
• Deltoid (posterior) *Latissimus dorsi
• Pectoralis major (clavicular The abduction joint
• Super Spinous joint
• Deltoid mid
• adduction
• Latissimus
• Pectoralis major

Integrated Function of the Shoulder Complex

• When the ST & GH there is Upward rotation of the scapula on the chest about 50 to 60° of motion during shoulder elevation
• There is total art motion of aboutGH total arch is about 180° of movement and
• During movements the two segments move together rather than sequentially (at same time)
• Scapulohumeral rhythm = setting phase: up to at best - Overall ratio =
• Ratio varies at different points in the ROM (ratio to 2 ratio for GH to 1 ratio for of S motion) It allows for the Scapulo- thoracic joint couples Trapezius:
• Upper Fibers
• Lower Fibers Serratus Anterior

Coupled Motions

• Glenohumeral Flexion for the following are needed.
• Elevation
• Posterior tilting
• Internal rotation at first: rotation starts to move/change External rotation
• The Sternoclavicular need the
• Elevation
• Rotation
• Protraction
• Acromioclavicular joint needs Horizontal + Sagittarius: it helps a good of movement

Glenohumeral abduction

• The Scapulothoracic
• Upper Motion with this joint With is when the Sternoclavicular joint and the needs following: Elevation Posterior rotation Retraction
• Acromioclavicular joint
• A.k.a Sagittarius plane needs a good amount of movement: *horizontal+ movement

The Glenohumeral Joint: Lateral/medial

GlenoHumal rotation needs a Scapulo- Thorasic joint (protraction/ Retraction is happening) and SternoClavicular movement needs protraction.

This lesson introduces the shoulder complex, which consists of the acromioclavicular, sternoclavicular, glenohumeral, and scapulothoracic joints. It reviews the structures of these joints and discusses passive and active components. Also, it describes the kinematics, arthrokinematics and integrated function of the shoulder complex.