Shoulder Complex Anatomy PDF

Introduction to the Shoulder Complex  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 O...

Introduction to the Shoulder Complex  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 Objectives complex Describe the kinematics & arthrokinematics of the joints of the shoulder complex Describe the integrated function of the shoulder complex  The Shoulder Complex 4 mechanically interrelated articulations Involves sternum, clavicle, ribs, scapula, & humerus Designed for mobility Passive structures don’t provide major stability Depends on dynamic stability Muscular control for stability during active movements Muscle forces are 1° mechanism to secure shoulder girdle to thorax  Joints of the Shoulder Complex Sternoclavicular (SC) Joint Acromioclavicular (AC) Joint Scapulothoracic (ST) “Joint” Glenohumeral (GH) Joint Sternoclavicul ar Joint  Sternoclavicular Joint Only structural attachment b/w axial skeleton & shoulder/UE Articulation of medial clavicle with manubrium of sternum & 1st costal cartilage Synovial, saddle joint At rest, jt space is wedge- shaped & open superiorly  Osteokinematics of SC Joint 3 rotational dof Elevation/depression of clavicle Based on motion of lateral Protraction/retraction of clavicle clavicle Anterior/posterior rotation of clavicle Long-axis rolling motions of entire clavicle 3 translatory dof Very small in magnitude in healthy joint Osteokinematics of SC Joint Elevation & depression occur near frontal plane Protraction & retraction occur near transverse plane Rotation occurs around longitudinal axis (indicated by dashed green line) Anterior view with translatory motions at medial clavicle & Superior view with translatory motions elevation/depression shown at medial clavicle & protraction/retraction shown  Osteokinematics of SC Joint: Clavicular Motions Elevation ROM: up to 48° Full range of elevation 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 Acts as pivot point for medial end of clavicle during movements Transects jt into 2 cavities Limits medial translation of clavicle Improves jt stability 1st costal cartilage 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 Supported by 3 ligament complexes: Anterior & posterior sternoclavicular ligaments Bilaminar costoclavicular ligament Interclavicular ligament  Sternoclavicular Capsule & Ligaments Thick posterior capsule 1° restraint to both anterior & posterior clavicular translations Anterior & posterior sternoclavicular ligaments Reinforce the capsule Limit anterior & posterior translation of medial clavicle Sternoclavicular Capsule & Ligaments Costoclavicular ligament Very strong ligament composed of 2 bundles Both limit clavicle elevation 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 Sternoclavicular Capsule & Ligaments Interclavicular ligament Limits excessive depression of clavicle Protects brachial plexus & subclavian artery 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 Arthrokinematics of SC Joint 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 Arthrokinematics of SC Joint Clavicular Rotation Occurs as a spin b/w the joint surfaces & disc Clavicle rotates primarily posteriorly from neutral Axis of rotation runs longitudinally through clavicle, intersecting the SC & Acromioclavic ular Joint  Acromioclavicular Joint Articulation b/w lateral clavicle & acromion of scapula Incongruent plane, synovial joint 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 Assists in force transmission from UE to clavicle Acromioclavicular Joint 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, fibrocartilaginous union b/w clavicle & acromion With UE use over time joint space develops May leave a “meniscal homologue” w/in the joint Fibrocartilage remnant (disc) varies in size among individuals and b/w the shoulders of same individual  Acromioclavicular Capsule and Ligaments Capsule of AC jt is relatively weak Reinforced by: Superior acromioclavicular ligament Inferior acromioclavicular ligament Coracoclavicular ligaments  Acromioclavicular Capsule & Ligaments Superior acromioclavicular ligament: Resists anteriorly directed forces applied to lateral clavicle Reinforced by aponeurotic fibers of trapezius & deltoid muscles Superior ligament stronger than inferior capsule and Acromioclavicular Capsule and Ligaments Coracoclavicular ligament: Divided into: Conoid ligament More triangular & vertically oriented Trapezoid ligament Quadrilateral  Acromioclavicular Capsule and Ligaments Coracoclavicular ligament: Conoid portion Primary restraint to inferior translation of acromion relative to lateral clavicle Trapezoid portion Restraint to posterior translations of lateral clavicle Plays a role in coupling posterior relative to acromion clavicle rotation & scapula upward rotation during UE elevation Both portions limit upward rotation of the scapula at the 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 plane of the scapula Internal/external rotation Anterior/posterior tilting Upward/downward rotation Resting Position of Scapula Superior view: scapula resting in internally Lateral view: scapula rotated position 35° - anteriorly tilted ~10° 45° anterior to - 15° from vertical coronal (frontal) plane Resting Position of Scapula 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 also occur at AC jt  Motions at the Acromioclavicular Joint 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 Motions at the Acromioclavicular Joint Internal & External Rotation Motions at the Acromioclavicular Joint Anterior and Posterior Tilting Occur around oblique “coronal” axis Anterior tilting Acromion moves forward & inferior angle moves posteriorly Posterior tilting Acromion moves backward & inferior angle moves anteriorly Motions at the Acromioclavicular Joint Anterior & Posterior Tilting Anterior tilting occurs in combination with scapular elevation Posterior tilting occurs in combination with scapular depression Motions at the Acromioclavicular Joint Upward & Downward Rotation Occurs around oblique “A-P” axis, Upward rotation Glenoid fossa tilts upward & inferior angle moves laterally Downward rotation Glenoid fossa tilts downward & inferior angle moves medially  Motions at the Acromioclavicular Joint Isolated 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 coracoclavicular ligaments  “opens” the AC joint, allowing upward rotation to occur Stability of AC Joint Not an inherently stable joint 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 Scapulothorac ic “Joint” Scapulothoracic “Joint” Formed by anterior surface of scapula and the thorax Not a true anatomic joint SC & AC jts 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: Integrity of the AC joint & SC joint Muscle strength and control Dynamic stabilization Internally rotated 35° - 45° Upwardly rotated 5° - Anteriorly tilted 10° - 15° 10° Scapula rests on posterior thorax ~5 cm from midline b/w 2nd – 7th ribs Significant variability in scapular rest position, even among Scapulothoracic Kinematics Rotational movements Upward/downward rotation Internal/external rotation Anterior/posterior tilting Scapulothoracic elevation/depression & protraction/retraction are considered translatory motions  Scapulothoracic Kinematics Upward/Downward Rotation Upward rotation is principal motion of scapula during active elevation of arm Full upward rotation of scapula requires: Elevation at sternoclavicular joint Clavicular posterior rotation Upward rotation at the AC joint  Scapulothoracic Kinematics Elevation and Depression Scapulothoracic elevation Clavicular elevation Small adjustments at AC jt for IR/ER or ant/post tilting to maintain contact with thorax Scapulothoracic Kinematics Scapular Protraction Protraction of clavicle Internal rotation at AC jt Scapular retraction Retraction of clavicle External rotation at AC jt Full scapular protraction results in an anteriorly facing glenoid Scapulothoracic Kinematics Internal/External Rotation Normally accompany protraction/retraction of clavicle at SC joint ~ 15° of IR occurs at AC jt with normal elevation of the arm Excessive IR of scapula on thorax causes increased prominence of medial border of scapula (Scapular winging) May indicate pathology or poor neuromuscular control of the scapulothoracic muscles (esp the serratus anterior) Scapulothoracic Kinematics Anterior and Posterior Tilting Primarily occur at the AC jt May couple with rotation of clavicle at SC jt Excessive anterior tilting can result in prominence of inferior angle of the scapula May be caused by poor neuromuscular control, faulty posture, and/or muscle tightness (pec minor) Muscle Actions of the Scapulothoracic Joint Scapular Protraction Serratus anterior Pectoralis major Pectoralis minor Scapular Retraction Middle trapezius Rhomboids  Muscle Actions of the Scapulothoracic Joint Scapular Elevation Upper trapezius Levator Scapular scapulae Depression Rhomboids Lower trapezius Latissimus dorsi Pectoralis minor  Muscle Actions of the Scapulothoracic Joint Scapular Downward Rotation Rhomboids Latissimus dorsi Levator scapulae Scapular Upward Pectoralis minor Rotation Upper trapezius Serratus anterior Lower trapezius Glenohumeral Joint Glenohumeral 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 Articular surfaces Glenoid fossa: shallow concavity Orientation of glenoid varies with respect to resting position of scapula Often slightly tilted upward Fossa is not always in a plane perpendicular to plane of the scapula Anteversion - glenoid fossa faces slightly anterior with respect to plane of scapula Retroversion – glenoid fossa faces slightly posterior  Glenoid Anteversion & Retroversion Most commonly the glenoid is in slight retroversion (6° - 7°) Anterior Posterior  Glenohumeral Joint Articular surfaces Humeral head Forms 1/3 to 1/2 of a sphere Articular surface area is larger than that of the glenoid When the arms hang dependently at the side, the articular surfaces of GH joint have little contact with one another Glenohume ral Joint Angle of inclination Formed by an axis through humeral head & neck in relation to a longitudinal axis through the humeral shaft Normally b/w 130° - 150° Glenohumer al Joint Angle of torsion Formed by an axis through the humeral head and neck in relation to an axis through the humeral condyles  Glenohumera l Joint Normal - slightly retroverted angle of humeral torsion Centers humeral head on glenoid fossa when scapula is in resting position & arm is at side Excessive retroversion or anteversion Alters position of humeral head in the glenoid May predispose to injury Glenohumeral Joint: Accessory Structures Glenoid labrum Surrounds and is attached to glenoid fossa  enhances articular surface Enhances depth/concavity of fossa by ~50% Resists humeral head translations Protects bony edges of fossa Minimizes GH friction Dissipates jt contact forces Attachment site for long head of biceps and glenohumeral ligaments Glenohumeral Capsule & Ligaments Large, loose jt 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 Glenohumer al Joint Rotator interval capsule Comprised of: Superior GH capsule Superior GH ligament Coracohumeral ligament Bridges gap b/w supraspinatus and subscapularis tendons  Glenohumeral Joint Ligaments Superior, middle, & inferior GH ligaments - thickened regions w/in jt capsule Superior GH ligament Runs from superior glenoid labrum to upper neck of humerus Deep to coracohumeral ligament With rotator interval capsule structures, it limits anterior & inferior translations of humeral head when the arm is at the side Glenohumeral Joint Ligaments Middle GH ligament Runs obliquely from superior ant. labrum to ant. proximal humerus Limits anterior humeral translation with the arm at side & up to 60° of abduction Inferior glenohumeral ligament complex (IGHLC) 3 components Anterior & posterior ligament bands Axillary pouch in between Position-dependent variability in function  Glenohumeral Joint Ligaments IGHLC function 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 ABD + ER Anterior band of IGHLC fans out anteriorly to provide anterior joint stability  resists anterior & inferior humeral head translation ABD + IR Posterior band of IGHLC fans out posteriorly to provide posterior joint stability  resists posterior & inferior humeral head translation  Glenohumeral Joint Ligaments Coracohumeral ligament Originates at base of coracoid process Comprised of 2 bands One inserts into edge of supraspinatus tendon & onto greater tubercle 2nd band inserts into subscapularis & lesser tubercle Form a tunnel for tendon of the long head of the biceps Limits inferior translation of humeral head in dependent arm position Resists humeral lateral rotation with the arm adducted  Coracoacromial Arch and Bursa Coracoacromial Arch Formed by: Coracoid process Undersurface of acromion Coracoacromial ligament Inferior surface of AC joint Creates an osteoligamentous “vault” over the humeral head Area b/w humeral head and arch is subacromial space  Subacromial Space Aka suprahumeral space Contents of subacromial space Subacromial bursa (reduces friction b/w humeral head and tendons) Rotator cuff tendons Long head of biceps tendon Measured as acromiohumeral interval on x-rays Healthy individuals: ~10 mm with arm at side and ~5 mm with arm elevated OH Glenohumeral Kinematics Flexion/Extension Pure GH flexion is ~ 120° Pure GH extension is ~ 50° Medial/Lateral Rotation ROM varies with position Rotation with arm at side is less than when abducted Abduction/Adduction ER of humerus is needed for full ABD Allows greater tubercle to pass under or behind Open pack position of GH joint: coracoacromial arch 50-55° ABD, 30° HADD “Scaption” Scaption: abduction in the 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 Normal Arthrokinematics arthrokinematics with shoulder ABD Abduction of GH jt requires an inferior slide of humeral head for normal ROM to occur W/o an inferior ABD arthrokinematics slide to Superior roll of humeral counteract the head superior roll, the Inferior slide of humeral humeral head head will impinges on coracoacromial Glenohumeral Arthrokinema tics As the articular surface slides inferiorly with abduction, the axis of rotation of humerus shifts slightly superiorly Glenohumeral Arthrokinemat ics Flexion & Extension Humeral head largely spins in place Flexion: humeral head spins with slight posterior slide Extension: humeral head spins with slight  Glenohumeral Arthrokinematics Medial (Internal) Rotation Lateral (External) Humeral head rolls Rotation anteriorly & slides posteriorly Humeral head rolls Stabilization of the Dependent Arm at Rest Downward pull of gravity is opposed by passive tension in rotator interval capsule Resultant force stabilizes humeral head on glenoid fossa Other factors assisting in holding humeral head in place at rest: Joint capsule creates a negative intra-articular pressure (a relative vacuum) Dynamic Stabilization of the Glenohumeral Joint Dynamic stabilization is related to: Force of the prime mover or movers Force of gravity Force of the muscular stabilizers Articular surface geometry Passive capsuloligamentous forces Force of friction within joint Joint reaction force  Dynamic Stabilization of the Glenohumeral Joint FD = action line of all 3 deltoids Resultant pull: Large translatory component (Fx) Small rotary component (Fy) Isolated contraction of deltoid would cause more superior translation than rotation of humerus  Dynamic Stabilization of the Glenohumeral Joint Rotator cuff muscles Major contribution to dynamic stability of GH jt Net force of ITS creates some rotation of humerus, & compresses humeral head into glenoid RTC tendons blend with & reinforce jt capsule Dynamic Stabilization of the Glenohumeral Joint Rotator cuff muscles Inferiorly directed line of pull offsets superior translation force of deltoid Creates force couple to produce rotation of humeral head with minimal translation  Dynamic Stabilization of the Glenohumeral Joint Supraspinatus Line of pull does not offset superior translation of deltoid Contributes to jt compression Relatively large MA allows it to independently produce nearly full GH ABD Gravity acts as stabilizing synergist Offsets small upward translatory pull of muscle Force Couple of GH Joint Dynamic Long head of biceps tendon Appears to center the humeral head in Stabilization of fossa & reduce vertical and anterior Glenohumeral translations of humeral head Joint Questionable significance  Flexion Extension Deltoid (anterior) Deltoid (posterior) Pectoralis major Latissimus dorsi (clavicular head) Triceps brachii (long head) Biceps brachii Pectoralis major (sternal Coracobrachialis head) Teres major Abduction Adduction Supraspinatus Pectoralis major Muscle Actions Deltoid (middle) Latissimus dorsi at the GH Joint Teres major Coracobrachialis Medial (Internal) Rotation Lateral (External) Rotation Pectoralis major Infraspinatus Subscapularis Teres minor Teres major Deltoid (posterior) Latissimus dorsi Integrated Function  Integrated Function of the Shoulder Complex ST & GH Function Upward rotation of scapula on thorax contributes 50-60° of motion during shoulder elevation GH + ST motion creates total arc of ~180° for shoulder complex ABD & flexion The 2 segments move together rather than sequentially Integrated Function of the Shoulder Complex Scapulohumeral rhythm "setting phase" up to ~30° of elevation Overall ratio of 2° of GH to 1° of ST motion during arm elevation Ratio varies at different points in the ROM  Scapular Force Couples Upward Rotation Downward Rotation Upper trap, serratus anterior, & Levator scap, rhomboids, & pec  Coupled Motions with Glenohumeral Flexion Upward rotation Posterior tilting Scapulothora Internal rotation initially, followed by cic Joint external rotation in higher ranges of flexion Elevation Sternoclavicu Posterior rotation lar Joint Protraction Upward rotation Acromioclavic Horizontal & sagittal plane rotational ular Joint adjustments  Coupled Motions with Glenohumeral Abduction Upward rotation Posterior tilting Scapulothora Internal rotation initially, followed by cic Joint external rotation in higher ranges of abduction Elevation Sternoclavicul Posterior rotation ar Joint Retraction Upward rotation Acromioclavicu Horizontal & sagittal plane rotational lar Joint adjustments  Coupled Motions with Glenohumeral Lateral Rotation & Medial Rotation Questions ?