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Biomechanics of Shoulder Complex.
Prepared by: Dr. Faryal Zaidi MSPT(KMU), BSPT(UHS), T-dpt*(KMU)
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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?
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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???
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Shoulder complex
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OSTEOLOGY
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SHOULDER COMPLEX Five Functional Joints 1. Glenohumeral Joint 2. Subacromial 3. Scapulothroasic 4. Acromioclavicular 5. Sternoclavicular
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SC JOINT Clavicle articulates with manubrium of the sternum
Weak bony structure but held by strong ligaments 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
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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 Rotation Ant. 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 Acromioclavicular Coracoacromial:
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. The fibers of the superior AC ligament are reinforced by aponeurotic fibers of the trapezius and deltoid muscles, which makes the superior joint support stronger than the inferior. The trapezoid ligament is quadrilateral in shape and is nearly horizontal in orientation. The conoid ligament, medial and slightly posterior to the trapezoid, is more triangular and vertically oriented.
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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.
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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 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
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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
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SUBACROMIAL SPACE Primary Impingement Secondary Impingement
Structural stenosis of subacromial space Secondary Impingement Functional stenosis of subacromial space due to abnormal arthrokinematics
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Glenohumeral Joint Three degrees of freedom Stability provided by
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 freedom Stability 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.
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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°: 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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