Shoulder Anatomy & Biomechanics PDF

The Shoulder Complex JOHN DAMIAO, PHD, MS, OTR/L Shoulder Complex Made up of 4 joints Bones: Sternum, clavicle, scapula, and humerus Functionally: Increases Range of motion for the upper extremity and therefore, the ability to manipulate objects in different planes What occupations are impacted w...

The Shoulder Complex JOHN DAMIAO, PHD, MS, OTR/L Shoulder Complex Made up of 4 joints Bones: Sternum, clavicle, scapula, and humerus Functionally: Increases Range of motion for the upper extremity and therefore, the ability to manipulate objects in different planes What occupations are impacted with decreased shoulder function? Osteology Shoulder Complex Consists of: ◦ Sternum ◦ Clavicle ◦ Scapula ◦ Humerus Osteology The Scapula Osteology The Humerus Four Joints Sternoclavicular (SC) Joint Arthrology: ◦ articulation between sternum and clavicle ◦ synovial; saddle-type of articulation (Bi-concave) ◦ the only UE joint that articulates to the axial skeleton Arthrokinematics ◦ rolling and sliding, spinning Sternoclavicular (SC) Joint Bi-concave: Clavicle: Convex for superior/inferior movement Concave for anterior/posterior movements Sternum: ??? Sternoclavicular Joint 3 Degrees of Freedom frontal plane: elevation 45o , depression 10o horizontal plane: protraction 15o, retraction 30o longitudinal axis (near sagittal plane): 40-50o of posterior rotation of the clavicle Review of the Convex-Concave Rule Concave on Convex (Convex-Concave): ◦A Concave surface moves on a Convex Surface ◦Rolls and Slides in the SAME Direction Convex on Concave (Concave-Convex): ◦ A convex surface moves on a Concave Surface ◦ Rolls and Slides in Opposite Directions *Posterior Roll-Spinning-Only occurs during Shoulder Abduction Acromioclavicular (AC) Joint ARTHROLOGY Articulation between acromion process and lateral end of the clavicle Gliding (Plane) Joint - Therefore the arthrokinematics of rolling/sliding are not applicable. Arthrokinematics are not well defined-different sources report 5-30 degrees in each plane ARTHROKINEMATICS stable; subtle sliding movements of the scapula; (in contrast to SC joint, which allows greater movement for the scapula) which allows optimal mobility and fit between scapula and thorax Acromioclavicular Joint Rotation Adjustments in ER/IR Anterior/Posterior Tilt Upward/Downward Rotation AC Joint Protaction: AC Joint will IR to contour around chest Elevation: AC Joint will tilt anteriorly, downward rotation Abduction: Upward rotation to about 30 degrees Scapulothoracic (ST) Joint Not a true joint but an articulation plane between the anterior surface of the scapula over the posterior-lateral surface of the thorax Scapula glides over the thorax and typically follows its shape Scapulothoracic joint movements are composites of AC and SC movements. Clinically, a decrease in movement of one joint will be compensated by the other. Resting Position of the Scapula Between 2nd and 7th Rib Medial Border is 6cm lateral to the spine Anterior Tilt: 10 degrees ***30-35 degrees of IR*** ***Plane of the Scapula*** Elevation -superior sliding of the scapula Depression -inferior sliding of the scapula Protraction-anterolateral sliding of the scapula away from the midline Retraction -posteromedial sliding of the scapula towards the midline Upward Rotation - the inferior border moves in superior- lateral direction; the glenoid fossa faces upward Downward Rotation - the inferior border moves in inferior- medial direction; the glenoid fossa faces downward Breaking it Down… ST Elevation: SC joint elevates (convex on concave); AC joint downward rotation/Anterior Tilt ST Protraction: SC joint protracts (concave on convex); AC joint internally rotates Abduction (ST upward rotation): SC joint elevates, AC joint upward rotation Movements of the Shoulder Complex Glenohumeral Acromioclavicular Flexion/extension Rotation of the scapula Abduction/adduction (acromion) Internal/external rotation Protraction/abduction and retraction/adduction Sternoclavicular Upward/downward rotation Elevation/depression Protraction/retraction Rotation of clavicle Movements of the Shoulder Complex (cont.) Scapulothoracic (bone- muscle-bone) Elevation/depression Protraction/retraction Upward/downward (medial/lateral) rotation Winging Tipping Glenohumeral Joint Complex synovial joint Ball and socket configuration between a convex humeral head and a concave glenoid fossa Loosely fitted and only made stable by its surrounding tissues Humerus/Scapula Articulation Head of Humerus retroverted 30 degress from the coronal plane Humerus is parallel to the plane of the scapula Glenoid fossa oriented anteriorly, with 5 degree upward tilt relative to its medial border Glenohumeral (GH) Joint Favors mobility over stability Glenoid fossa only covers 1/3 of the surface area of the humeral head Comparable to a golf ball rolling on a surface the size of a quarter The bony fit of the GH joint does not offer much stability. Therefore, the GH joint relies on outside factors to maintain the integrity of the joint Periarticular Connective Tissue Fibrous Capsule: GH Joint is surrounded by a fibrous capsule The fibrous capsule is loose fitting and expandable Allows the humeral head to be pulled away from the fossa a significant distance without causing pain or trauma The inferior portion, which is slackened at rest, is called the axillary pouch Glenohumeral Capsular Ligaments Thicken the external layers of the anterior and inferior walls of the joint capsule. Limits the extremes of GH movement Superior GH Lig-taught in adduction Middle GH Lig-taught in anterior translation, external rotation Inferior GH Lig-consists of anterior band, posterior band, and axillary pouch o Anterior-Taught in ER, 90 degrees abduction o Axillary Pouch-Abduction o Posterior-Internal Rotation, 90 degrees abduction Capsular Mechanics for the Glenohumeral Joint Capsule Part Taut Superior Adduction or resting position Inferior 90 degrees abduction Anterior External rotation Posterior Internal rotation Posteroinferior Retrain to posterior dislocation Rotator Cuff Muscles and Long Head of the Biceps Provide further structural reinforcement Form a cuff that protects and ACTIVELY STABILIZES the GH joint The muscle bellies provide support as they surround the capsule Tendons of the muscles blend into the capsule Long Head of the Biceps Originates Supraglenoid Tubercle and Glenoid Labrum Crosses over the humeral head Through the bicipital groove (Intertubercular groove) Restricts Anterior Translation Important in Abduction Glenoid Labrum Fibrocartilage Ring over glenoid fossa 50% overall depth of the glenoid fossa is attributed to the labrum Deepens the fossa, thus increasing the contact area for the humeral head Recap!!!! What are the tissues that Reinforce or Deepen the GH Joint? Joint Capsule Capsular Ligaments Rotator Cuff Muscles (Subscapularis, Infraspinatus, Teres Minor, Supraspinatus) Long head of the Biceps Brachii Glenoid Labrum Scapulothoracic Posture and Static Stability SCS = Superior Capsular Structures (Supraspinatus Tendon, superior capsula ( TAUGHT ADDUCTION) ligament, coracohumeral ligament ALL THESE STRUCTURES PUSH INTO GELNOFOSSA CREATES STATIC LOCK MECHANISM G = Gravity CF = Compression force When combining the SCS force vector with the force vector produced by gravity, a compressive locking force is formed at a 90 degree angle. Additionally, the glenoid fossa, at rest, is upwardly rotated, creating a shelf for the humeral head to rest Loss of the upward rotation of the glenoid fossa will decrease Kinematics Three degrees of freedom: ◦Flexion and Extension ◦Abduction and Adduction ◦Internal Rotation and External Rotation A fourth motion is defined: Horizontal Adduction/Abduction ***What planes do these actions occur in? https://www.youtube.com/watch?v=5YeJro5ESVI GH Flexion/Extension Spinning of humeral head Flexion to 120 degrees To reach 180 degrees requires upward rotation of the scapula During extension, scapula tilts anteriorly FORWARD GH Internal/External Rotation Convex-on-concave rule External Rotation: Rolls??? Slides??? o Answer: Posterior Roll, Anterior Slide Internal Rotation: Rolls??? Slides??? o Answer: Anterior Roll, Posterior Slide GH Abduction Grossly: Superior Roll with an Inferior Glide Six Kinematic Principles: ◦ 1. Based upon the 2:1 Scapulohumeral Rhythm, active shoulder abduction to 180 degrees occurs with 120 degrees glenohumeral joint abduction, with 60 degrees ST upward rotation ◦ 2. The 60 degrees of upward rotation at the ST joint is a result of composite elevation at the SC joint and upward rotation at the AC joint. ◦ 3. The clavicle retracts about 15 degrees. ◦ 4. The scapula tilts posteriorly and externally rotates (net external rotation due to clavicle retraction-allows for subacromial space to be maintained ◦ 5. The clavicle rotates posteriorly-due to the coracoclavicular ligament becoming taught during scapular upward rotation. Contributes to posterior tilt of the scapula ◦ 6. The humerus externally rotates-Allows the greater tubercle to pass posterior to acromion process+++ https://www.youtube.com/watch?v=3VygGuBObVc Brachial Plexus The entire upper extremity receives its innervation primarily through the brachial plexus. C5-T1 nerve roots Upper trunk (C5-C6), Middle Trunk (C7), Lower Trunk (C8-T1) Subdivisions: Anterior and Posterior Cords: Lateral, Posterior, Medial Nerves Muscles of the Shoulder Most can fall into two categories: Proximal stabilizers or distal mobilizers. Proximal Stabilizers: ◦Originate on spine, ribs, cranium ◦Insert on the scapula and clavicle Distal Mobilizers: ◦Originate on the scapula or clavicle and insert at the humerus or forearm. ST Elevators Upper Trapezius Levator Scapulae Rhomboids ST Depressors Lower Trapezius Latissimus Dorsi Pectoralis Minor ST Protraction ST Retraction Serratus Anterior Middle Trapezius Pectoralis Minor Rhomboids Lower trapezius (To Counteract Elevation) Upward Rotation/GH Abduction At the ST Joint, the Upper Trapezius, Lower Trapezius, and Serratus Anterior work together to drive the upward rotation of the scapula and provide stable attachments for the distal mobilizers. The trapezius originate from the occipital protuberance to the spinous process of T12 and insert at the lateral clavicle, acromion, spine of the scapula. The upper trapezius pulls the clavicle/acromion superiorly/medially The lower trapezius pulls the spine of the scapula inferiorly/medially The serratus anterior pulls the inferior angle upward and laterally All three forces act simultaneously. This is called Force Coupling Upward Rotation/GH Abduction GH Prime Moves: Middle Deltoid and Supraspinatus Contribute about equal shares to overall abduction If the deltoid is paralyzed, the supraspinatus can still abduct the arm If the supraspinatus is paralyzed, full abduction is often difficult due to the altered arthrokinematics at the shoulder. Rotator Cuff Muscles During Elevation of the Arm The rotator cuff muscles are: Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis *The distal attachments of this muscle group blend into the capsule before inserting onto the humerus-providing more stability to the GH joint. *The supraspinatus produces a compression force on the humeral head into the glenoid fossa while rolling the head superiorly. *The other rotator cuff muscles provide an inferiorly-directed force (both anterior and posterior)-inferior slide *The infraspinatus and teres minor can externally rotate the humeral head as necessary to provide clearance of the greater tubercle as it approaches the acromion Scapulohumeral Rhythm Phase One: Resting Phase NOTHING HAPPEN Phase Two: Setting Phase ◦ 0-30 degrees abduction ◦ SC joint elevates ◦ AC joint upward rotation 0-10 degrees ◦ ST joint 10 degrees of winging and tipping ◦ Deltoid provides a superiorly directed force ◦ All rotator cuff muscles are engaged ( TO KEEP MUSCLE FROM PULLIING OUT OF SOCKET) Scapulohumeral Rhythm (Cont.) Phase Three: ◦ 30-90 degrees of abduction ◦ 2:1 Ratio-during this phase: 60 degrees GH movement; 30 degrees ST movement ◦ SC joint elevates, clavicle rotates posteriorly ◦ AC joint: Upward rotation ◦ ST joint: Posterior tilt and upward rotation ◦ Humerus externally rotates Phase Four: ◦ 90-180 degrees of abduction ◦ 2:1 Ratio continues-180 degrees=120 degrees GH movement; 60 degrees ST movement ◦ Clavicle continues to rotate posteriorly ◦ ST joint upward rotation ◦ Inferior force from infraspinatus, teres minor and subscapularis ◦ Revolving door. ( EVERTHING MOVING IN SYNERGIESTIC WAY) GH Flexion Prime Movers: Anterior Deltoid Pectoralis Major (Upper Fibers) NEED TO RELAX TO GO TO A CEARTAIN POINT) Biceps Brachii Adduction/Extension Latissimus Dorsi Teres Major Posterior Deltoid Pectoralis Major Triceps Brachii (long head) *The entire rotator cuff is active to stabilize the GH joint Downward Rotation of the Scapula Rhomboids Levator Scapulae Pectoralis Minor (assists with anterior tilt with shoulder extension) *Accompanies adduction/extension at the GH joint Internal Rotation Subscapularis Anterior Deltoid Pectoralis Major Latissimus Dorsi Teres Major External Rotation Posterior Deltoid Infraspinatus Teres Minor (antagonist to Teres Major) Small torque potential- leads to tendency for internally rotated posture and for strain to ligaments. Let’s think about Function… What are some occupations that would be impacted by having difficulty with performing the following? Shoulder abduction. RASING YOUR HAND IN CLASS Shoulder Flexion Shoulder Internal Rotation Shoulder External Rotation (WASHING/ COMBING YOUR HAIR SWINGING BAT( BOTH INTERNAL/ EXTERNAL) ( PUTTING ON A CAR SEAT) Shoulder Adduction/Extension ( BOWELING) Conditions Resource: Shoulder Pathology Sensations Sprains Clicking Snapping Strains Grating Locking or catching Tendonitis Warmth Bursitis Contusion Adhesive Capsulitis (frozen shoulder) Fracture Clavicle Shoulder Impingement Syndrome Scapula Thoracic Outlet Syndrome Humerus Subluxation Dislocation Any Questions???