Prepared by:

Dr. Faryal Zaidi MSPT(KMU), BSPT(UHS), T-dpt*(KMU)

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Biomechanics of Shoulder Complex.

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

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What is biomechanics? 3

Biomechanics

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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.

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Why study biomechanics?

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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.)

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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.

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kinematics

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Kinetics

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

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Kinetics

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Biomechanics VS kinesiology???13

Shoulder complex

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OSTEOLOGY

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SHOULDER COMPLEX

Five Functional Joints1. Glenohumeral Joint2. Subacromial3. Scapulothroasic4. Acromioclavicular5. Sternoclavicular

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SC JOINT

Clavicle articulates with manubrium of the sternumWeak bony structure but held by strong ligamentsFibrocartilaginous 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

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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

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LIGAMENTS OF SC JOINT

LIGAMENTS:• Interclavicular Lig.• Costoclavicular Lig.• Posterior Ligament

Sternoclavicular

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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

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MOVEMENTS OF SC JOINT

• Elevation (48 degree)– limited by costoclavicular

• Depression (less than15 degree) – limited by first rib

Axial RotationAnt. Rot. (very limited – 10 degree)Post. Rot. (50 degree)

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Axial rotation

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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

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AC JOINT

LIGAMENTS:• Coracoclavicular

– Medial: Conoid– Lateral: Trapezoid

• Acromioclavicular– Superior – Inferior

• Coracoacromial: – Coracoids process to acromiom process

• Closed packed position iswhen the humerus is abducted to 90 degree.

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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

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Anterior/posterior tipping

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Upward/downward rotation

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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

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SUBACROMIAL SPACE

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Structures Within Suprahumeral Space

1. Long head of biceps2. Superior capsule3. Supraspinatus tendon4. Upper margins of subscapularis & infraspinatus tendons5. Subacromial bursa6. Inferior surface ofthe A-C joint

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SUBACROMIAL SPACE

Clinical RelevanceAvoidance 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

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SUBACROMIAL SPACE

• Primary ImpingementStructural stenosis of subacromial space• Secondary ImpingementFunctional stenosis of subacromial space dueto abnormal arthrokinematics

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Glenohumeral Joint

Ball and socket, synovial joint in which round head of humerus articulates with shallow glenoid fossa of scapula stabilized slightly by fibrocartilaginous rim called the Glenoid

Labrum 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 freedomStability provided by• Passive restraints• Active restraints

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GH ARTICULATING SURFACES

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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

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GH LIGAMENTS

• SGHL• MGHL• IGHL• Anterior band• Posterior band• Axillary band

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Restraints to External Rotation

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

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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

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Restraints to Inferior Translation

• Dependent on arm position• 0° - SGHL, C-H• 90° - IGHLC

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Glenohumeral Motion

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

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Arthrokinematics of the GH Joint

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CONVEX-CONCAVE RULE

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DOWNWARD GLIDE

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Scapulo thoracic (ST) Joint

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)

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ST Joint

During humeral elevation (flexion, abduction and scaption) scapula and humerus must move in synchronous fashion

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

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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

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MOVEMENTS OF THE SCAPULA

• Upward/Downward Rotation

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