KB - Shoulder PDF

The Shoulder Complex Dr. Rami Said, PT, DPT, MEng K&B I – Shoulder The Shoulder Complex 4 Joints of the Shoulder Complex Sternoclavicular (SC) Joint Acromioclavicular (AC) Joint Anatomical Glenohumeral (GH) Joint Scapulothor...

The Shoulder Complex Dr. Rami Said, PT, DPT, MEng K&B I – Shoulder The Shoulder Complex 4 Joints of the Shoulder Complex Sternoclavicular (SC) Joint Acromioclavicular (AC) Joint Anatomical Glenohumeral (GH) Joint Scapulothoracic (ST) Joint Functional Function Links the upper extremity to the trunk via the SC Joint Provides extensive mobility of the arm in space Provides stability for fine/gross motor movements at the elbow, wrist, and hand K&B I – Shoulder  Alignment/Positional Relationships Scapula 3 angles: inferior, superior, and lateral 3 borders: medial (vertebral), lateral (axillary), superior Resting position of scapula: Superior angle aligned with spinous process (SP) of Thoracic Vertebra 2 (T2) Base/Root of the Spine of the Scapula aligned with SP of T3 Inferior angle aligned with SP of T7 3 inches from medial border to SP Slight upward rotation of the scapula by 5º- 10º in the frontal plane Acromion vertically aligned with mastoid process Anterior tilt (tipping) of the scapula =https://www.thieme-connect.de/products/ebooks/pdf/10.1055/b-0034-71062.pdf 10º https://blackstonelabs.com/blogs/weekly-blog/a-head-above-the-rest- posture-series-part-1-improving-your-neck-alignment-and-head-position K&B I – Shoulder Alignment/Positional Relationships Plane of the Scapula Scapula sits on the conical thoracic cage in a 30º to 45º angle to the frontal plane, directed anteriorly The glenoid fossa will be directed anteriorly Most activities of daily living are performed in the plane of the scapula to decrease stress on the joint capsule and musculature K&B I – Shoulder Alignment/Positional Relationships The movement of elevation in the plane of the scapula = “scaption” Optimal length-tension relationship between abductors and rotators  Rotator cuff (supraspinatus) & deltoid are optimally aligned to perform scaption https://musculoskeletalkey.com/shoulder-6 K&B I – Shoulder Alignment/Positional Relationships Humerus Angle of inclination of the humerus is 135º between the humeral shaft and head, in the frontal plane Humeral head is rotated posteriorly 30º to 45º to match the scapular plane = retroversion of the humerus Both the angle of inclination and retroversion of the humerus increases stability of the glenohumeral joint K&B I – Shoulder Alignment/Positional Relationships Clavicle Curved ‘S’-like shaft, that sits in a resting position that is angled 20º posterior to the frontal plane of the body and slightly above the horizontal plane https://www.informedhealth.org/how-does-the-shoulder-work.3484.en.html K&B I – Shoulder The Sternoclavicular Joint K&B I – Shoulder SC Joint The SC joint is the only true articulation of the upper extremity to the axial skeleton Diarthrodial saddle joint Reciprocally convex along the long axis (superior-inferior) of the clavicle and concave along the transverse axis (anterior-posterior) Clavicular rotation contributes to increased ROM of the shoulder Acts as a site of muscular attachment, protection to neurovasculature, and transmits force to the scapula Stability depends on bony articulation, ligaments, muscles, and capsule K&B I – Shoulder SC – Periarticular Connective Tissue Costoclavicular Ligament Principle stabilizing structure of the SC joint that attaches the clavicle to the 1st rib Limits all movements of the clavicle, except depression Anterior & Posterior SC Ligaments Capsular ligaments that limit excessive anterior and posterior movement (shear stress) Interclavicular Ligament Connects both SC joint, spanning the jugular notch Articular Disc Fibrocartilage that attenuates shock and helps to prevent dislocation K&B I – Shoulder SC – Movement 3 degrees of freedom of movement: Elevation/Depression Protraction/Retraction Posterior Rotation K&B I – Shoulder SC – Elevation/Depression Osteokinematics Occurs in the frontal plane through an anterior-posterior axis of rotation that goes through the costoclavicular ligament Elevation = 45º Depression = 5º - 15º Arthrokinematics Elevation = convex clavicular head rolls superiorly and slides inferiorly on the concave sternum Depression = convex clavicular head rolls inferiorly and slides superiorly K&B I – Shoulder SC – Protraction/Retraction Osteokinematics Occurs in the transverse plane through a vertical axis of rotation that goes through the costoclavicular ligament Protraction = 15º - 30º Retraction = 15º - 30º Arthrokinematics Protraction = concave clavicle rolls and slides anteriorly on the convex sternum Retraction = concave clavicle rolls and slides posteriorly on the convex sternum K&B I – Shoulder SC – Posterior Rotation Osteokinematics Occurs in the sagittal plane through a longitudinal axis that goes through the clavicle Begins at 90º of shoulder flexion, abduction, or scaption, the clavicle posteriorly rotates 20º – 35º Arthrokinematics Posterior spin of the clavicular head about the articular disc K&B I – Shoulder The Acromioclavicular Joint K&B I – Shoulder AC Joint Plane synovial joint that has 3 degrees of freedom made up of the convex lateral end of the clavicle and the concave acromion process of the scapula*** Function Maintains an appropriate relationship between the scapula and clavicle, early and late in the overall ROM of the upper extremity K&B I – Shoulder AC – Periarticular Connective Tissue Coracoclavicular Ligament Base of coracoid process to inferior surface of the clavicle Primary stabilizing structure of the AC joint Divided into 2 parts: Conoid Ligament = limits clavicular elevation & posterior rotation and scapular upward rotation & posterior tipping Trapezoid Ligament = limits clavicular elevation and reduces shear force at AC joint Superior & Inferior AC Ligaments Reinforce the joint capsule, prevent posterior dislocations, and limits scapular tipping K&B I – Shoulder AC – Movement 3 degrees of freedom of movement: Upward/Downward Rotation (Frontal Plane Adjustments) Internal/External Rotation (Horizontal Plane Adjustments) Anterior/Posterior Tilting (Sagittal Plane Adjustments) K&B I – Shoulder AC – Movement Osteokinematics Movement of the scapula relative to the clavicle Upward/Downward Rotation = 30º each Horizontal / Sagittal Plane Adjustments occur, but have been difficult to measure, thus no consensus on ranges of motion  they optimally align the scapula against the thoracic cage Internal Rotation & Anterior Tilting are associated with Scap Protraction & Elevation External Rotation & Posterior Tilting are associated with Scap Retraction & Depression Arthrokinematics No consensus K&B I – Shoulder The Scapulothoracic Joint K&B I – Shoulder ST Joint Not a true anatomical joint, but functions as a joint Comprised of the convex thoracic cage and the concave scapula Scapular motion functions to move the orientation of the glenoid fossa and allow a stable base for the humeral head during arm movement Lies in the scapular plane (not truly in the frontal plane) K&B I – Shoulder ST – Periarticular Connective Tissue Predominantly scapulothoracic musculature that guides movement and provides dynamic stability at the ST joint No static stabilizers at the ST joint K&B I – Shoulder ST – Movement 3 degrees of freedom of movement Elevation/Depression (Frontal Plane) Protraction/Retraction (Transverse Plane) Upward/Downward Rotation (Frontal Plane) K&B I – Shoulder ST – Elevation/Depression Osteokinematics Movement coordination of the SC and AC joints is required for complete ST joint movement Elevation = scapula translates superiorly via elevation at the SC joint and downward rotation at the AC joint, which keeps the scapula vertical during elevation Depression = scapula translates inferiorly via depression at the SC joint and upward rotation at the AC joint, which keeps the scapula vertical during depression Arthrokinematics No consensus K&B I – Shoulder ST – Protraction/Retraction Osteokinematics Lateral or medial translation of the scapula on the thoracic cage Protraction = scapula moves away from the spine via protraction at the SC joint and internal rotation at the AC joint Retraction = scapula moves toward the spine via retraction at the SC joint and external rotation at the AC joint Arthrokinematics No consensus K&B I – Shoulder ST – Upward/Downward Rotation Osteokinematics Important for the glenoid fossa to face superiorly during overhead movements Upward Rotation = scapula rotates upward (glenoid fossa faces superiorly) via elevation at the SC joint and upward rotation at the AC joint Downward Rotation = scapula rotates downward (glenoid fossa faces inferiorly) via depression at the SC joint and downward rotation at the AC joint Arthrokinematics No consensus K&B I – Shoulder K&B I – Shoulder The Glenohumeral Joint K&B I – Shoulder GH Joint Diarthroidal ball-and-socket joint that is the most mobile joint in the body Humeral Head = large, convex spherical “ball” that faces medial, superior, & posterior Glenoid Fossa = small, concave ovoid that faces lateral, superior, & anterior Only 25% - 33% of the humeral head can articulate with the glenoid fossa because of the difference in size between the two Mobility is maximized but stability is sacrificed K&B I – Shoulder GH – Periarticular Connective Tissue Glenoid Labrum Fibrocartilage that surrounds the rim of the glenoid fossa to deepen the fossa and make it 50% larger Increases the articular contact area to improve osseous stability and articular congruity Decreases the amount of humeral head translation K&B I – Shoulder GH – Periarticular Connective Tissue Capsuloligamentous Complex Joint capsule that surrounds the GH joint from the rim of the glenoid fossa to the anatomical neck of the humerus Allows for extensive mobility Creates the axillary pouch Coracohumeral Ligament Connects coracoid process to greater tubercle Strongest supporting ligament of GH joint Pulled taut during shoulder ER, Flexion, and Extension Primary restraint to inferior and posterior translation in an adducted arm Counteracts pull of gravity on the arm https://link.springer.com/chapter/10.1007/978-3-030-19285-3_1 K&B I – Shoulder GH – Periarticular Connective Tissue Glenohumeral Ligaments Anterior thickening of the joint capsule, that provides increased joint stabilization Limits translation and rotation of the humeral head to reduce extreme ranges of motion SGHL Taut with full adduction, inferior, & AP humeral translation MGHL Resists anterior translation of humerus at 45º-60º of abduction and ER IGHL Anterior band = taut in 90º of abduction and full ER Posterior band = 90º of abduction and full IR https://link.springer.com/chapter/10.1007/978-3-030-19285-3_1 K&B I – Shoulder GH – Periarticular Connective Tissue Coracoacromial Arch Coracoacromial Ligament & Acromion Process creates the “Roof” of the GH Joint Protects superior migration of the humeral head into the bony structures Creates the subacromial space, which houses the supraspinatus muscle, subacromial bursa, long head of the biceps, and the joint capsule Often a site of shoulder impingement due to poor mechanics of movement https://link.springer.com/chapter/10.1007/978-3-030-19285-3_1 K&B I – Shoulder GH – Static Stability Primary Glenoid fossa is oriented upward by 5º - 10º by muscles In this position, the passive tension of the superior capsular structures (SCS – joint capsule & coracohumeral ligament) plus the force of gravity create a compression force (CF)  stabilizing the humeral head into the glenoid fossa Secondary Supraspinatus and deltoid are active forces that further support the static stability K&B I – Shoulder GH – Dynamic Stability With minimal bony congruity, passive stability, comprised from the periarticular connective tissue (ligaments, labrum, bone congruency, & joint capsule) is not enough When structural / passive stability is insufficient for adequate joint stability, dynamic joint stability is necessary Dynamic joint stability relies heavily on active muscle contraction K&B I – Shoulder GH – Movement 3 degrees of freedom of movement: Flexion/Extension (Sagittal Plane) Abduction/Adduction (Frontal Plane) Internal/External Rotation (Transverse Plane) Horizontal Abduction/Adduction (Transverse Plane) * K&B I – Shoulder GH – Flexion/Extension Osteokinematics Sagittal plane movement around a medial-lateral axis of rotation Flexion = 120º (60º more comes from ST joint) Extension = 65º - 80º Arthrokinematics Flexion = (a) posterior spinning of humeral head (b) anterior roll and posterior glide* Extension = (a) anterior spinning of humeral head (b) posterior roll and anterior glide* K&B I – Shoulder GH – Abduction/Adduction Osteokinematics Frontal plane movement around an anterior-posterior axis of rotation Abduction = 120º (60º more comes from ST joint) Adduction = 30º - 50º Arthrokinematics Abduction = convex humeral head rolls superiorly and glides inferiorly Adduction = convex humeral head rolls inferiorly and glides superiorly K&B I – Shoulder GH – Flexion/Abduction The size discrepancy between the humeral head and glenoid fossa is a critical reason why the arthrokinematics are so important during abduction/flexion Rolling without inferior/posterior gliding or pure spinning in the glenoid fossa can result in impingement of the subacromial tissues K&B I – Shoulder GH – Internal/External Rotation Osteokinematics Horizontal plane movement around a vertical (longitudinal) axis ROM in neutral abduction ER = 60º - 70º IR = 75º - 85º ROM in 90º abduction ER = 90º IR = 70º Arthrokinematics ER = convex humeral head rolls posteriorly and slides anteriorly IR = convex humeral head rolls anteriorly and slides posteriorly K&B I – Shoulder GH – Horizontal Abduction/Adduction Osteokinematics Horizontal plane movement around a vertical (longitudinal) axis H-ADDuction (H-Flexion) = 135º H-ABDuction (H-Extension) = 45º Arthrokinematics H-ADD = convex humeral head rolls anteriorly and slides posteriorly H-ABD = convex humeral head rolls posteriorly and slides anteriorly http://shouldercomplex.weebly.com/movements.html K&B I – Shoulder The Scapulohumeral Rhythm K&B I – Shoulder The Scapulohumeral Rhythm Simultaneous and synchronous series of kinematic movement of all 4 shoulder joints, contributing to the overall movement at the shoulder complex into flexion, abduction, or scaption Begins after the first 30º of movement Function Permits greater ROM with improved stability Humeral head stays in an optimal position Muscles maintain a good length-tension relationship to optimally function https://www.gobeyondphysicaltherapy.com/blog-1/fc93drsjsgfmkctz87bdt67cs4eslr K&B I – Shoulder Scapulohumeral Rhythm Principles Principle #1 2:1 ratio of GH abduction/scaption to ST upward rotation resulting in a total of 180º of shoulder motion 120º of GH abduction/scaption 60º of ST upward rotation For every 2º of GH movement, the ST moves 1º Principle #2 60º of ST upward rotation is a result of 30º elevation from the SC joint and 30º upward rotation from the AC joint K&B I – Shoulder Scapulohumeral Rhythm Principles Principle #3 During full abduction/scaption, 20º retraction at the SC joint occurs Principle #4 During full abduction/scaption, the scapula posteriorly tilts 20º and externally rotates 5º to increase sub-coracoacromial space, align the scapula flush on the thoracic cage, and orient the glenoid fossa to allow greater stability during movement K&B I – Shoulder Scapulohumeral Rhythm Principles Principle #5 25º - 30º of posterior rotation of the clavicle occurs along the longitudinal axis as the coracoclavicular ligament tightens during scapular movement, to allow the last 30º of scapular upward rotation Principle #6 GH joint external rotates 35º - 40º to allow the greater tubercle to pass under the acromion and reduce the risk of impinging the subacromial structures K&B I – Shoulder Muscle Function of the Shoulder Complex K&B I – Shoulder Biomechanics Review The line of action of a muscle will be dictated by its origin and insertion and the axis of rotation of the joint it crosses Resolve the muscle action line into components to understand its role in movement and joint stability Compression forces tend to stabilize, while rotary forces tend to mobilize K&B I – Shoulder Functional Movement Muscles work together to produce purposeful movement but are not limited to moving in the cardinal planes alone Functionally, our bodies/joints move 3-dimensionally by utilizing: Force couples Synergistic actions K&B I – Shoulder Axioscapular Muscles K&B I – Shoulder Axioscapular Muscles Function Position the scapula in the right place to provide a stable base for movement of the upper extremity Muscles Trapezius Serratus Anterior Levator Scapula Rhomboids Pectoralis Minor K&B I – Shoulder Axioscapular – Trapezius Action Upper Trapezius = elevation Middle Trapezius = retraction Lower Trapezius = depression Together, they contract to contribute to upward rotation of the scapula Innervation Spinal Accessory Nerve (CN XI) K&B I – Shoulder Axioscapular – Trapezius Underactive (often the middle / lower trap fibers) Poor elevation, upward rotation, or stabilization of the scapula during movement Rounded shoulder posture Overactive (often the upper trap fibers) Elevated scapula, ipsilateral lateral flexion at neck Functional Movement Anything that involves raising the arm past the first 30º of movement into flexion, abduction, or scaption Reaching overhead; Washing/brushing your hair K&B I – Shoulder Axioscapular – Serratus Anterior Action Scapular abduction, upward rotation, and elevation Scapular abduction + upward rotation = Protraction Stabilizes the medial border of the scapula on the thoracic cage Innervation Long Thoracic Nerve K&B I – Shoulder Axioscapular – Serratus Anterior Underactive (typical) “Winging” of the scapula = abnormal scapular IR during movement (medial border protrudes away from the thoracic cage) Compensations may occur vs. true weakness due to other joint limitations For example, apparent winging due to lack of GH IR ROM, causing the scapula to tilt anteriorly when reaching behind the back Tightness (atypical) Protracted scapula Functional Movement Pushing; Punching; Reaching forward; https://www.researchgate.net/figure/Scapular-winging-on-the- right-noted-by-prominence-of-the-medial-border_fig8_257557663 Throwing K&B I – Shoulder Upward Rotation Force Couple Synergistic action of the trapezius and serratus anterior muscles to upwardly rotate the scapula Trapezius adducts as the serratus anterior abducts the scapula, simultaneously, resulting in both upwardly rotating the scapula Upper Trap = elevates the distal clavicle and acromion Middle Trap = adducts the scapula Lower Trap = depresses the medial spine of the scapula Serratus Anterior = elevates and abducts the anterior surface of the inferior angle of the scapula K&B I – Shoulder Axioscapular – Levator Scapula Action Elevates and downwardly rotates the scapula Lateral flexion, ipsilateral rotation, and extension at the cervical spine Innervation Dorsal Scapular Nerve K&B I – Shoulder Axioscapular – Levator Scapula Underactive (atypical) Depressed scapula Overactive (typical) Downward rotated scapula Elevated scapula Ipsilateral lateral flexion of neck Functional Movement Reaching backward; Pulling, Turning head K&B I – Shoulder Elevation Force Couple Synergistic action of the Upper Trapezius and Levator Scapula to elevate and suspend the scapula and clavicle during scapular elevation Upper Trapezius = elevates and upwardly rotates Levator Scapula = elevates and downwardly rotates Resultant motion is pure elevation and suspension of the shoulder K&B I – Shoulder Axioscapular – Rhomboids Action (Rhomboid Minor/Major work together) Scapular adduction = retraction Downward rotation Stabilize the scapula to the thoracic cage Innervation Dorsal Scapular Nerve K&B I – Shoulder Axioscapular – Rhomboids Underactive (typical) Rounded/Protracted shoulders Overactive (atypical) Adducted and Downwardly rotated scapula Functional Movement Rowing; Pulling; Reaching behind the back K&B I – Shoulder Retraction Force Couple Synergistic action of the middle trapezius, lower trapezius, and rhomboids Primary Mover = Middle Trapezius Secondary Mover = Rhomboids, Lower Trapezius The upward rotation and depression of the lower trapezius is neutralized by the downward rotation and elevation of the rhomboids Resulting in pure retraction K&B I – Shoulder Axioscapular – Pectoralis Minor Action Anterior Tilt of scapula Depression of scapula Downward Rotation of the scapula Innervation Medial & Lateral Pectoral Nerves K&B I – Shoulder Axioscapular – Pectoralis Minor Underactive (atypical) Poor scapular stability during weightbearing tasks Overactive (typical) Anterior tilt of scapula Rounded shoulders Increased risk of impingement via the increased scapular IR during movement that occurs Functional Movement Pushing downward to rise out of a seat or using assistive devices for gait (ie, crutches) K&B I – Shoulder Downward Rotation Force Couple Synergistic action between Rhomboids, Levator Scapula, & Pectoralis Minor Pec Minor = Anterior tilt (abducts), downward rotation, and depress scapula Levator Scapula / Rhomboids = adduct, downward rotation, and elevate scapula Resulting action = scapular downward rotation Functional Movement Return from upward rotation during swimming, crawling, closing windows Movements that involve scapular adduction with GH extension K&B I – Shoulder Axiohumeral Muscles K&B I – Shoulder Axiohumeral Muscles Function Gross motor movers of the glenohumeral joint Muscles Latissimus Dorsi Pectoralis Major K&B I – Shoulder Axiohumeral – Latissimus Dorsi Action Extension, adduction, & IR of humerus Raises body toward arms during climbing Innervation Thoracodorsal Nerve K&B I – Shoulder Axiohumeral – Latissimus Dorsi Underactive Decreased powerful strength in above motions Overactive Limits shoulder flexion, ER Increased lumbar lordosis and anterior pelvic tilt Indirectly increases thoracic kyphosis Functional Movement Swinging; Throwing; Climbing; Pulling K&B I – Shoulder Axiohumeral – Pectoralis Major Action Flexion, adduction, IR, horizontal adduction of humerus Clavicular fibers = flexion, horizontal adduction, and IR Sternocostal fibers = adduction and extension from a flexed position Innervation Medial and Lateral Pectoral Nerves K&B I – Shoulder Axiohumeral – Pectoralis Major Underactive Decreased strength/power in actions Overactive Limited ROM in horizontal abduction, ER, and scapular retraction Functional Movement Swinging; Throwing; Climbing; Pushing K&B I – Shoulder Shoulder Girdle Depression Combined movement from axioscapular and axiohumeral depressors: Lower Trapezius Pec Minor / Pec Major Latissimus Dorsi Open chain depression = reaching towards the ground Closed chain depression = raising the body off a seat or using an assistive device to ambulate (crutches, cane) https://www.physio-pedia.com/Crutches K&B I – Shoulder Shoulder Girdle Protraction Combined movement from axioscapular and axiohumeral protractors: Serratus Anterior – protracts the scapula forward Pec Major – pulls the humerus forward Open chain protraction = reaching forward, punching Closed chain protraction = raising the body off the floor, pushup https://breakingmuscle.com/fitness/3-ways-to-build-lean-muscle-with-bodyweight-exercise K&B I – Shoulder Scapulohumeral Muscles K&B I – Shoulder Scapulohumeral Muscles Function Provide motion and dynamic stabilization to the GH joint Muscles Deltoid Supraspinatus Infraspinatus Teres Minor Subscapularis Teres Major Coracobrachialis K&B I – Shoulder Scapulohumeral – Deltoid Action Abduction of humerus Anterior Deltoid = flexion, horizontal adduction, IR Middle Deltoid = abduction Posterior Deltoid = extension, horizontal abduction, ER Innervation Axillary Nerve K&B I – Shoulder Scapulohumeral – Deltoid Underactive (typical) Abduction of the arm by supraspinatus compensation, scapular upward rotation, and lateral trunk flexion Overactive (atypical) Limited ROM in all movements of the GH joint Functional Movement Raising the arm in all directions, but particularly out to the side K&B I – Shoulder Scapulohumeral – Supraspinatus Action Abduction in scapular plane Posterior fibers = ER Stabilization of the GH joint Innervation Suprascapular Nerve K&B I – Shoulder Scapulohumeral – Supraspinatus Underactive (typical) Decreased strength and endurance of shoulder Shoulder impingement Overactive (atypical) Limited ROM into adduction Functional Movement Works with deltoid to start the movement of abduction Stabilization of the humerus into the glenoid with all UE movement K&B I – Shoulder Scapulohumeral – Infraspinatus/Teres Minor Action ER of GH joint Horizontal Abduction Innervation Infraspinatus = Suprascapular Nerve Teres Minor = Axillary Nerve K&B I – Shoulder Scapulohumeral – Infraspinatus/Teres Minor Underactive (typical) Decreased ER strength and endurance of shoulder Shoulder impingement Tightness (atypical) Limited ROM into IR & horizontal adduction Functional Movement Stabilization of the humerus into the glenoid with all UE movement K&B I – Shoulder Scapulohumeral – Subscapularis Action IR of humerus Innervation Upper & Lower Subscapular Nerves Underactive Decreased strength of IR Anterior instability of GH joint Shoulder impingement Overactive Limited ER ROM Functional Movement Stabilization of the humerus into the glenoid with all UE movement K&B I – Shoulder Scapulohumeral – Teres Major Action Extension, adduction, IR of humerus Innervation Lower Subscapular Nerve Underactive Decreased extension, adduction, IR strength Overactive Limited ROM of ER, flexion, abduction Abducts scapula, contributing to rounded shoulders Functional Movement ”little brother” to the Latissimus Dorsi Climbing; Pulling; Crawling; Swimming; Swinging; Throwing K&B I – Shoulder Shoulder Girdle Extension Combined movement from axioscapular, axiohumeral, & scapulohumeral muscles: Rhomboids & Lower Traps = stabilize the scapula (opposite actions) Teres Major & Latissimus Dorsi = extends the humerus Open chain extension = pulling an object Closed chain extension = pulling the body towards fixed hands (pullups) https://www.vectorstock.com/royalty-free-vector/man-climbing-silhouette-climber-on-cliff-vector-26381670 K&B I – Shoulder Scapulohumeral – Coracobrachialis Action Flexion, Adduction, IR Innervation Musculocutaneous Nerve Underactive (atypical) Decreased flexion strength Overactive (atypical) Limited extension, ER Functional Movement Assists in activities that involve shoulder flexion, adduction, and IR K&B I – Shoulder Functional Shoulder Flexion Anterior Deltoid – active throughout ROM Coracobrachialis / Long Head of Biceps – assists in first 90º of motion Scapulothoracic abductors and upward rotators continue the remaining GH flexion movement https://www.acefitness.org/fitness-certifications/ace-answers/exam-preparation-blog/3535/muscles-that-move-the-arm/ K&B I – Shoulder Function K&B I – Shoulder Functional Abduction / Scaption Deltoids & Supraspinatus = primary movers Both initiate movement As the arm approaches 90º , both provide a compression force to increase stability Upward rotation of scapula allows for a better length-tension relationship for continued movement and stabilization Rotator cuff muscle activity increases stability of the humerus into the glenoid https://orthop.washington.edu/patient-care/articles/shoulder/rotator-cuff-relevant-anatomy-and-mechanics.html K&B I – Shoulder Deltoid Function FD = Action Line of Deltoid Fx = Large Translatory& Compression Component Causes superior translation and if unopposed, then the humeral head will impact the coracoacromial arch Adds compression = stabilization Fy = Small Rotatory Component Combines with rotatory force of supraspinatus to begin abduction of arm https://www.slideshare.net/debashreeroy7/biomechanics-of-shoulder-complex K&B I – Shoulder Supraspinatus Function FSUP = Action Line of Supraspinatus Fx = Small Translatory Component Causes superior translation and if unopposed, then the humeral head will impact the coracoacromial arch Fy = Large Rotatory & Compression Component Combines with the rotatory force of deltoid to begin abduction of arm Adds compression = stabilization https://www.slideshare.net/debashreeroy7/biomechanics-of-shoulder-complex K&B I – Shoulder Rotator Cuff Function Rotator cuff act as humeral head depressors and stabilizers Synergistically contract during flexion, abduction, and scaption Stabilizes the humeral head into the glenoid fossa Counteracts the superior translation force of the deltoid https://www.researchgate.net/figure/The-glenohumeral-force-couple-The-resultant-force-action-of-the-rotator-cuff-muscles_fig1_7595778 K&B I – Shoulder Dynamic Stability of Arthrokinematics Deltoid Superior roll of humerus Supraspinatus Superior roll of humerus Infraspinatus/Teres Minor/Subscapularis Work synergistically to provide an inferior translation or depression of the humerus (glide) K&B I – Shoulder Functional Internal Rotation Subscapularis = Primary Mover Teres Major / Latissimus Dorsi = IR when arm is moving into adduction and extension Pec Major = IR when arm is moving into adduction and flexion https://www.kingofthegym.com/subscapularis/ K&B I – Shoulder Functional External Rotation Infraspinatus / Teres Minor / Posterior Deltoid = Primary Movers Supraspinatus assists with ER when GH joint is in neutral K&B I – Shoulder Relationship of Shoulder to Spine Direct musculoskeletal relationships between the spine and shoulder girdle as many muscles attach from cervical and thoracic spines to the shoulder girdle Full shoulder movement is dependent on some cervical and thoracic movement, as well as the static position or dynamic movement of the lumbar spine and rib cage (to be discussed later in course) Poor posture is often related to poor shoulder and spine posture in sitting and standing positions K&B I – Shoulder K&B I – Shoulder