Biomechanics of Shoulder Complex Prepared by Dr Faryal

Biomechanics of Shoulder Complex. Prepared by: Dr. Faryal Zaidi MSPT(KMU), BSPT(UHS), T-dpt*(KMU) 1

OBJECTIVES At the end of this lecture students should be able to: • Define different terms of biomechanics • Identify different structures in shoulder complex • Explain kinetics and kinematics of shoulder joint • Describe different pathologies of shoulder complex 2

What is biomechanics? 3

Biomechanics 4

Biomechanics • The term biomechanics combines the prefix bio, meaning “life, ” with the field of mechanics, which is the study of the actions of forces, (both internal muscle forces and external forces. ) In biomechanics we analyze the mechanical aspects of living organisms. 5

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Why study biomechanics? 7

Subdivisions • statics: study of systems in constant motion, (including zero motion) • dynamics: study of systems subject to acceleration • kinematics: study of the appearance or description of motion • kinetics: study of the actions of forces (Force can be thought of as a push or pull acting on a body. ) 8

kinematics • What we visually observe of a body in motion is called the kinematics of the movement. Kinematics is the study of the size, sequencing, and timing of movement, without regard for the forces that cause or result from the motion. The kinematics of an exercise or a sport skill is known, more commonly, as form or technique. 9

kinematics 10

Kinetics • Kinetics is the study of forces, including internal forces (muscle forces) and external forces (the forces of gravity). 11

Kinetics 12

Biomechanics VS kinesiology? ? ? 13

Shoulder complex 14

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OSTEOLOGY 17

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SHOULDER COMPLEX Five Functional Joints 1. Glenohumeral Joint 2. Subacromial 3. Scapulothroasic 4. Acromioclavicular 5. Sternoclavicular 21

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SC JOINT Clavicle articulates with manubrium of the sternum q. Weak bony structure but held by strong ligaments q. Fibrocartilaginous disk between articulating surfaces • Shock absorber and helps prevent displacement forward • Clavicle permitted to move up and down, forward and backward and in rotation • Clavicle must elevate 40 degrees to allow upward rotation of scapula and thus shoulder abduction 23

SC JOINT • The only attachment of the upper extremity to axial skeleton • Plane synovial joint with degree of freedom 6, having joint capsule, joint disk and three major ligaments • Movement of the SC joint produces scapular movements, if it is fused the equal amount of movement will occur at AC joint 24

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LIGAMENTS OF SC JOINT LIGAMENTS: • Interclavicular Lig. • Costoclavicular Lig. • Posterior Ligament Sternoclavicular 26

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MOVEMENTS OF SC JOINT Movements in horizontal plane: • Protraction (30 degree) limited by costoclavicular and post. capsule • Retraction (30 degree) limited by costoclavicular and ant. capsule 28

MOVEMENTS OF SC JOINT • Elevation (48 degree) – limited by costoclavicular • Depression (less than 15 degree) – limited by first rib Axial Rotation Ant. Rot. (very limited – 10 degree) Post. Rot. (50 degree) 29

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Axial rotation 31

AC JOINT • Lateral end of clavicle with acromion process of scapula • Weak joint and susceptible to sprain and separation • Joint capsule n two major ligaments and disk – present or absent 32

AC JOINT LIGAMENTS: • Coracoclavicular – Medial: Conoid – Lateral: Trapezoid • Acromioclavicular – Superior – Inferior • Coracoacromial: – Coracoids process to acromiom process • Closed packed position is when the humerus is abducted to 90 degree. 33

MOVEMENTS OF AC JOINT • Internal and external rotation – Bringing the glenoid fossa of the scapula anteromedially and posterolaterally, respectively • Anterior and posterior tiping or tilting – Ant. - acromion tipping forward and the inferior angle tipping backward – Post. - rotate the acromion backward and the inferior angle forward. • Upward and downward rotation – Upward rotation tilts the glenoid fossa upward and downward rotation is the opposite motion. 34

Internal/external rotation 35

Anterior/posterior tipping 36

Upward/downward rotation 37

CORACOACROMIAL ARCH Arch over the GH joint formed by Coracoacromial arch, acromion and coracoid process • Sub acromial space: area in between CA arch and humeral head • Supraspinatus tendon, long head biceps tendon, and sub acromial bursa • Subject to irritation and inflammation as a result of excessive humeral head translation or impingement from repeated overhead activity 38

SUBACROMIAL SPACE 39

Structures Within Suprahumeral Space 1. Long head of biceps 2. Superior capsule 3. Supraspinatus tendon 4. Upper margins of subscapularis & infraspinatus tendons 5. Subacromial bursa 6. Inferior surface of the A-C joint 40

SUBACROMIAL SPACE Clinical Relevance Avoidance of impingement during elevation of the arm requires • External rotation of humerus to clear greater tuberosity • Upward rotation of scapula to elevate lateral end of acromiom 41

SUBACROMIAL SPACE • Primary Impingement Structural stenosis of subacromial space • Secondary Impingement Functional stenosis of subacromial space due to abnormal arthrokinematics 42

Glenohumeral Joint Ball and socket, synovial joint in which round head of humerus articulates with shallow glenoid fossa of scapula q stabilized slightly by fibrocartilaginous rim called the Glenoid Labrum q Humeral head larger than glenoid fossa • At any point during elevation of shoulder only 25 to 30% of humeral head is in contact with glenoid Statically stabilized by labrum and capsular ligaments Dynamically stabilized by deltoid and rotator cuff muscles • Three degrees of freedom Stability provided by • Passive restraints • Active restraints 43

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GH ARTICULATING SURFACES 45

Glenoid Labrum • When the arms hang dependently at the side, the two articular surfaces of the GH joint have little contact. The majority of the time, the inferior surface of the humeral head rests on only a small inferior portion of the fossa. The total available articular • surface of the glenoid fossa is enhanced by an accessory structure, the glenoid labrum. This structure surrounds and is attached to the periphery of the glenoid fossa enhancing the depth or curvature of the fossa by approximately 50%. • the labrum was traditionally thought to be synoviumlined fibrocartilage, more recently it has been proposed that it is actually a redundant fold of dense fibrous connective tissue with little fibrocartilage other than at the attachment of the labrum to the periphery of the fossa. • The labrum superiorly is loosely attached, whereas the inferior portion is firmly attached and relatively immobile. The glenoid labrum also serves as the attachment site for the glenohumeral ligaments and the tendon of the long head of the biceps brachii. 46

GH CAPSULE • The entire GH joint is surrounded by a large, loose capsule that is taut superiorly and slack anteriorly and inferiorly in the resting position (arm dependent at the side). The capsular surface area is twice that of the humeral head. 39 More than 2. 5 cm of distraction of the head from the glenoid fossa is allowed in the loose-packed position. • The relative laxity of the GH capsule is necessary for the large excursion of joint surfaces but provides little stability without the reinforcement of ligaments and muscles. When the humerus is abducted and laterally rotated on the glenoid fossa, the capsule twists on itself and tightens, making abduction and lateral rotation the close-packed position for the GH joint 47

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GH LIGAMENTS • • • SGHL MGHL IGHL Anterior band Posterior band Axillary band 49

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Restraints to External Rotation • • Dependent on arm position 0° - SGHL, C-H & subscapular 45° - SGHL & MGHL 90° - anterior band IGHLC 51

Restraints to Internal Rotation • • Dependent on arm position 0° - posterior band of IGHLC 45° - anterior & posterior band of IGHLC 90° - anterior & posterior band of IGHLC 52

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Restraints to Inferior Translation • Dependent on arm position • 0° - SGHL, C-H • 90° - IGHLC 54

Glenohumeral Motion Scapular Plane: • • Flexion/extension - 120° Abduction/adduction - 120° External/internal rotation Horizontal abduction/adduction 55

Arthrokinematics of the GH Joint 56

CONVEX-CONCAVE RULE 57

DOWNWARD GLIDE 58

Scapulo thoracic (ST) Joint q Not a true joint, but movement of scapula on thoracic cage is critical to joint motion • Scapula capable of upward/downward rotation, external/internal rotation & anterior/posterior tipping • In addition to rotating other motions include scapular elevation and depression & protraction (abduction) and retraction (adduction) 59

ST Joint During humeral elevation (flexion, abduction and scaption) scapula and humerus must move in synchronous fashion Ø Often termed scapulohumeral rhythm • Total range 180°: 120° @ GH joint, 60° of scapular moments • Ratio of 2: 1, degrees of GH movement to scapular movement after 30 degrees of abduction and 45 to 6 degrees of flexion – Maintain joint congruency – Length-tension relationship for numerous muscles – Adequate subacromial space 60

Scapulo humeral rhythm – During humeral elevation • Scapula upwardly rotates • Posteriorly tips • Externally rotates • Elevates • & Retracts – Alterations in these movement patterns can cause a variety of shoulder conditions 61

MOVEMENTS OF THE SCAPULA • Upward/Downward Rotation 62