Introduction to the Shoulder Complex

Introduction to the Shoulder Complex

• The shoulder complex is made up of four joints: the sternoclavicular, acromioclavicular, scapulothoracic, and glenohumeral joints.
• The objectives are to discuss the joints that form the shoulder complex, and to review their structure, components, kinematics, arthrokinematics and integrated function.

The Shoulder Complex

• The shoulder complex includes 4 mechanically interrelated articulations.
• These articulations involve the sternum, clavicle, ribs, scapula, and humerus.
• The shoulder complex is designed for mobility.
• Passive structures do not provide major stability.
• It depends on dynamic stability, which involves the muscular control for stability during active movements.
• The shoulder girdle is secured to the thorax through muscle forces.

Joints of the Shoulder Complex

• The joints that make up the shoulder complex are the sternoclavicular (SC), acromioclavicular (AC), scapulothoracic (ST), and glenohumeral (GH) joints.

Sternoclavicular Joint

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

Osteokinematics of the SC Joint

• Possesses 3 rotational degrees of freedom.
• The three rotational motions are elevation/depression, protraction/retraction, and anterior/posterior rotation of the clavicle.
• It has 3 translatory degrees of freedom
• These motions are 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 a longitudinal axis.
• Elevation ROM: up to 48°.
• Full range of elevation 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°.

SC Disc and Capsule & Ligaments

• The SC disc acts as a pivot point for the medial clavicle’s movements.
• The SC disc transects it into 2 cavities.
• It limits medial translation of clavicle and improves stability by increasing congruence and absorbing forces.
• The SC joint has a relatively strong fibrous capsule supported by 3 ligament complexes.
• The ligaments are: Anterior & posterior sternoclavicular, bilaminar costoclavicular, and interclavicular ligament
• The thick posterior capsule is the 1° restraint to anterior and posterior clavicular translations.
• They reinforce the capsule and limit anterior & posterior translation of medial clavicle.
• The costoclavicular ligament is a very strong ligament composed of 2 bundles.
• Costoclavicular ligament limits clavicle elevation, with the posterior bundle also resisting medial translation.
• It serves as functional axis of rotation, absorbing & transmitting superiorly directed forces applied to clavicle.
• Interclavicular ligament limits excessive depression of clavicle.
• The interclavicular ligament, also protects brachial plexus & subclavian artery and limits superior gliding of medial clavicle on manubrium.

Arthrokinematics of SC Joint

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

• It is the articulation between the lateral clavicle and acromion of scapula.
• It is an incongruent plane, synovial joint with 3 rotational and 3 translational degrees of freedom.
• It allows scapula to move in 3 dimensions during arm movement, Increases upper extremity motion, and positions glenoid beneath humeral head.
• The AC joint helps maximize scapula contact with thorax.
• The AC joint also assists in force transmission from UE to clavicle.
• The AC joint can have variability in the shape of articular surfaces from flat to concave/convex.
• Its relatively vertical orientation of joint surfaces mean it is more susceptible to shearing forces which leads to degenerative effects.
• It is initially, a fibrocartilaginous union between clavicle & acromion.
• With UE use over time joint space develops, may leave a "meniscal homologue" within the joint.
• The Fibrocartilage remnant (disc) varies in size among individuals.
• The capsule is relatively weak, reinforced by the superior and inferior acromioclavicular ligament and the coracoclavicular ligaments
• Superior acromioclavicular ligament resists anteriorly directed forces applied to lateral clavicle.
• Reinforced by aponeurotic fibers of trapezius & deltoid muscles and is stronger than inferior capsule and ligament

Coracoclavicular Ligament

• The coracoclavicular ligament is divided into the conoid and trapezoid ligament.
• The conoid is more triangular & vertically oriented, providing primary restraint to inferior translation of acromion relative to lateral clavicle.
• The trapezoid is quadrilateral and oriented more horizontally, a restraint to posterior translations of lateral clavicle relative to acromion.
• Both portions limit upward rotation of the scapula at the AC joint.
• It plays a role in coupling posterior clavicle rotation and scapula upward rotation during UE elevation

Acromioclavicular Articulation Kinematics

• The axes of motion are difficult to define due to the variability in the articulating joint surfaces among individuals.
• Motions occur around axes oriented relative to the plane of the scapula
• These movements are internal/external rotation, anterior/posterior tilting, and upward/downward rotation.
• AC motion is also influenced by rotation of the clavicle.
• Small translations also occur at it, such as anterior/posterior, superior/inferior, and medial/lateral.
• Resting scapula will rest in internally rotated position 35° - 45° anterior to coronal (frontal) plane
• The lateral view is anteriorly tilted ~10° - 15° from vertical.
• The "longitudinal” axis of scapula at rest is upwardly rotated 5° - 10° from vertical.
• Internal rotation orients glenoid fossa anteromedially.
• External rotation orients glenoid fossa posterolaterally.
• Internal rotation & external rotation help maintain contact of scapula with curvature of thorax, positioning glenoid fossa toward plane of humeral elevation.
• Movement here maintains congruency & stability between humeral head & scapula and maximizes function of Glenohumeral muscles, capsule, ligaments.
• Anterior tilting occurs when Acromion moves forward & inferior angle moves posteriorly.
• When acromion moves backward & inferior angle moves anteriorly posterior tilting occurs.
• Anterior tilting is combined with scapular elevation, while posterior tilting happens with scapular depression.
• Glenoid fossa tilts upward & inferior angle moves laterally during upward rotation.
• Glenoid fossa tilts downward & inferior angle moves medially during downward rotation.
• Passive motion of upward/downward rotation at AC jt is limited by coracoclavicular ligament.
• With integrated active movement, Post. rotation of clavicle reduces tension of the ligaments which "opens" the AC joint, allowing upward rotation to occur.
• It is not an inherently stable joint and is susceptible to trauma & degenerative changes.
• Trauma related AC jt dysfunction is more common in first 3 decades of life.
• Contact sports or a fall on shoulder with the arm adducted is a trauma factor.
• Degenerative changes are more common later in life.

Scapulothoracic Joint

• Its formed by the anterior surface of scapula and the thorax and is not a true anatomic joint
• SC & AC joints are interdependent with the movement.
• Any movement results in movement at AC, SC, or both.
• Stability related to the integrity of the AC and SC joints as well as muscle strength and control, and dynamic stabilization.
• Resting scapula will rest on posterior thorax ~5 cm from midline and between 2nd – 7th ribs.
• There is significant variability in scapular rest position, even among healthy subjects.
• Rotational movements include: Upward/downward rotation, internal/external rotation, & anterior/posterior tilting.
• Scapulothoracic elevation/depression and protraction/retraction are translatory motions.
• Upward rotation occurs during active elevation of arm and requires elevation at sternoclavicular joint, clavicular posterior rotation, and upward rotation at AC joint.
• Muscular actions include Scapular protraction with serratus anterior pectoralis major and pectoralis minor
• It provides retraction with middle trapezius and rhomboids
• Elevation with upper trapezius, levator scapulae and rhomboids
• Depression with lower trapezius, latissimus dorsi and pectoralis minor
• Downward rotation with rhomboids, latissimus dorsi, elevator scapulae and pectoralis minor
• Upward Rotation with upper trapezius, serratus anterior and Lower trapezius

Scapulothoracic Kinematics

• Scapulothoracic elevation occurs with scapular and clvicular elevation.
• The small adjustments at AC are for IR/ER or ant/post tilting to maintain contact with the thorax.
• Scapular protraction requires protraction of the clavicle, also the internal rotation at AC joint.
• Scapular refraction means clavicle retraction and external rotation at the AC joint.
• With full scapular protraction the glenoid will face anteriorly
• Internal rotation and external rotation normally accompanies protraction/retraction of clavicle at SC joint.
• Approximately, 15° of internal rotation occurs at the AC joint with normal elevation of the arm.
• Excessive IR causes prominence of medial border of scapula.
• It may indicate pathology or neuromuscular control of the scapulothoracic muscles (serratus anterior).
• Anterior and posterior tilting occurs primarily at the AC.
• Anterior or posterior tilting may couple with rotation of clavicle at SC jt
• Excessive anterior tilting can result in prominence of inferior angle of the scapula.
• It may be caused by poor neuromuscular control, faulty posture, and/or muscle tightness of the pec minor.

Glenohumeral Joint

• Is a ball and socket, synovial joint with 3 rotary & 3 translatory dof
• It articulates between the humeral head and glenoid fossa and motions of scapula influence GH joint function
• It was designed for mobility but its reduced stability increases susceptibility to instability, injury and degenerative changes.
• Glenoid fossa has shallow concavity with its orientation varies with respect to resting position.
• Glenoid fossa is often slightly tilted upward.
• Fossas area, usually not in a plane perpendicular to plane of the scapula,
• The glenoid fossa faces slightly to the inferior angle of the scapula.

Glenohumeral Considerations

• Humeral head forms 1/3 to 1/2 of a sphere and the articular surface area is larger than of the glenoid.
• When the arms hang dependently, the articulating surfaces have little contact with one another.
• Angle of inclination - normally between 130° - 150° that was formed by way through humeral head & neck in relation to longitudinal axis through the humeral shaft
• Normally, in a slight retroverted angle of humeral torsion, when the scapula is in resting position & arm is at side, centers the humeral head on glenoid fossa
• Excessive retroversion or anteversion that alters the position of humeral head will pre-dispose to injury.
• Glenoid labrum surrounds and is attached to glenoid enhancement of articular surface area to increases depth/concavity by ~50% to resist humeral head translations.
• Minimizes GH friction and dissipates a lot contact forces
• Serves as attachment site for long head of biceps and glenohumeral ligaments
• The jt is taut superiorly and loose inferiorly when arm is at rest by the sid.
• Its maximally tightens when arm is fully abducted & externally rotated (close-packed position) and includes ligaments superior GH, middle GH, inferior GH and the coracohumeral ligaments

Rotator interval capsule

• The capsule comprised of superior GH capsule and the coracohumeral ligaments as a means of bridging gap that would otherwise come from the Supraspinatus tendon and Subscapularis tendon

Glenohumeral Joint Ligaments

• The ligaments are thickened regions within joint capsule: Superior, middle, & inferior GH ligaments.
• The superior glenohumeral ligaments ligament ligament go from superior glenoid labrum to the upper neck of humerus that are deep to coracohumeral and limits anterior and inferior translations of the humeral head when the arm is at the sides
• The middle glenohumeral ligaments run obliquely superior ant. from labrum to ant. proximal limiting humerus anterior translation when the arm at side & up to 60°

Inferior GH Ligament Complex

• IGHLC has 3 components, which are the anterior & posterior ligament bands and axillary pouch in between

• Position-dependent variability in function within the capsule provides jt stabilization when abd > 45° or with combined abd + rotation

• It also allows stability during anterior/posterior rotation, major role of jt stability

• ABD > 45°, the inferior capsule slack is taken up, and resists inferior humeral head translation

• With ABD + ER as the Anterior band of IGHLC fans out anteriorly for anterior tension in joint stability resists ant and inf

• When ABD and IR Posterior band tension and fans out posteriorly the ligament structure will provide post tension, resisting against the post and inf movement

• Coracohumeral ligament originates at base of coracoid process with its comprised of 2 bands while one inserts into edge of supraspinatus tendons and the 2nd is inserted subscapularis.

• Forms "tunnel” which is then responsible for allowing Long head of be able to function by limiting inferior translation in dependent arm

• Coracoacromial Arch formed by: Coracoid process, undersurface of acromion, inferior surface of AC joint, and the Coracoacromial ligament to vault is also subcromail space (suprahumeral space) b/w the head joint

Subacromial Space

• Contents include: subchromial bursa (reduce/friction humeral head/tendons).
• Measured as acromiohumeral interval which is ~10 mm normal but is normal with ELEVATION (~5mm) but may be
• Flexion/Extension with Pure GH flexion for around 120° and extension is 50° so rotations here are vary.
• Rotation with at side of the joint or from it to go from under the head.
• Abduction/Adduction, with Er then allows g tubercle to pass under or Behind coracoacomial Arch
• In an Open pack position the joint (50/55 degrees of Abduction by way of ER, rotation, adduction)
• Scaption: of frontal plane is 30-45 in ER because greater range of movement can be acquired

Rotator Cuff and Joint Dynamics

• Inferior slide of head for ER needs 120 with 30 of elevation 2-1 where its diff for each range of space the setting phase is 30.
• Inferior is slide counter that is roll and when that is limited will impinge arch by the shoulder
• Humeral rotation and external rotations means head will roll anteriorly with slides posterior and lateral movement.

Stabilization at Rest and Dynamic

• Stabilization force of 3 comes by force (gravity) which is tension that pulls is all together on the joint. This with the other factors and is helped through the slight tilt.
• Dynamic of Prime Moveer, gravity, stabilizers, joint area
• Dynamic through forces of the prime mover, gravity, muscle
• Line of pull to not off that translation force and creates of this in order to produce minimal translation
• For the most part large allowing independently full range of AD movements. With these synergist offsets small upward pull with muscle and gravity in its action

Force Couple & Muscle Actions at the Glenohumeral Joint

• The force of this is supraspinatus, ER infraspinatus and Teres and long head of biceps tendon to center the head in fossil, vert translation and question
• Flexion = Del anterior, pec major (clavicular head), bicep, coracobrachials
• Abduction= Del middle, supraspinatus
• Adduction corcaobrachiali, pec, lat, teres Lateral = infraspinatus, teres Medial= Pec, teres, lat, deltoid

Integrated Function

• Of elevation has up with in of by that arc of movements that allows us through 60 and 120 by moving these segments
• The ratios have scapulohumeral in by and different phases which will affect by where setting occurs

Force Couples

• Have to and or and and is by these muscle actions: In order that rotation and adjustments and movement can happen to in, it also have to by adjustments where adjustments in planes are occurring and

• When there by in will then have in rotation will then have

This lesson introduces the shoulder complex, which comprises the sternoclavicular, acromioclavicular, scapulothoracic, and glenohumeral joints. It reviews the structure, components, kinematics, arthrokinematics, and integrated function of these joints. The shoulder complex is designed for mobility and depends on dynamic stability.