1 Shoulder Biomechanics Lecture originally developed by Bryan Morrison, Ph.D. candidate Arizona State University Fall 2000 2 Outline Anatomy Biomechanics Problems
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Shoulder Biomechanics
Lecture originally developed by Bryan Morrison, Ph.D. candidate
Arizona State UniversityFall 2000
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OutlineAnatomyBiomechanicsProblems
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Shoulder ComplexGreatest ____________Greatest Predisposition for DislocationLittle _____ Stability (Mainly Ligaments)Range of Motion Starts at _____° or Greater in all Planes and Decreases with Age (activity slows this process)
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BonesHumerusClavicleScapulaRibs
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HumerusArticular Surface (33-55 mm)____° from Shaft32° Retroverted (Rotated ________)
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ScapulaGlenoid Fossa
41 by 25 mmPear Shaped_____ Degree Tilt (Posterior)(Retrotilted)
Glenoid LabrumJoint CapsuleGlenohumeral LigamentsLong Head of the Biceps Tendon
Minimal ___________ Contact (Large Range of Motion)
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JointsGlenohumeral ______________Acromioclavicular______________
Last 3 Collectively Called Shoulder Girdle
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LigamentsGlenohumeral
______________Superior, Middle, Inferior Glenohumeral
AcromioclavicularConoidTrapezoid
Sternoclavicular____________SternoclavicularCostoclavicular
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Glenohumeral Joint Movement
Flexion (___)/Extension (___) (Sagittal)Abduction(180)/Adduction(-75) (__________)Internal(___)/External Rotation(-90) (_____________) Horizontal Abduction(___) /Adduction(-45) (Flexion/Extension)Primarily Rotational (___)
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Elevation PlanesFrontalSagittalScapular
___________ Advantageous
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Shoulder Girdle MovementUpward/ Downward Rotation (______)Protraction/Retraction (________/________)(Transverse) Upward/ Downward Tilt (________)Elevation/Depression (_________)
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Elevation and Tilting
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Protraction and Rotation
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Large Range of MotionMotion Spread Through All articulations (Synchronous and Simultaneous)Glenoid Fossa Mobility (Scapular Motion)Optimal Portion of Length-Tension CurveMinimal Constraints
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Joint Movement PatternsMany Ways a Joint Could MoveGlenohumeral Joint Initial movement
__° Flexion__° Abduction
SpineReasons for Different Opinions
Measurement TechniquesPlanesAnatomic Variations
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Opinions on Movement
Doody (Scapular Plane)
Saha (Scapular Plane)
Poppen(Scapular Plane)
Freedman(Scapular Plane)
2/1 after 60°/30° - 120°/60° Total MotionInnman (1944) Flexion/Abduction
Glenohumeral/ Shoulder Girdle
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Codman’s ParadoxFlexHorizontally AbductAdductRotation with out Rotation
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Joint StabilityGlenoid Fossa
>___% Longitudinal Length>___% Transverse Length
_________ Tilt of Glenoid FossaHumeral Head RetroversionIntact Capsule and Glenoid Labrum
____________ PressureMuscular Function of the Rotator Cuff
SubscapularisSupraspinatusInfraspinatusUpper Teres Minor
•Glenoid Osteotomy
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Glenohumeral MusclesDeltoid (A, Middle, P)Rotator Cuff
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Teres MajorCoracobrachialis
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Scapulothoracic MusclesTrapeziusRhomboidsLevator Scapulae______________Pectoralis Minor
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Multiple Joint MusclesPectoralis MajorLatissimus DorsiBiceps BrachiiTriceps (_________)
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Muscular Motions Glenohumeral
Flex, Horiz. AddCoracobrachialis
Extend, Int. Rotation, Add, Horiz. Abd
Teres Major
Int. RotationSubscapularis
Teres Minor
Infraspinatus
Abduct, Int. RotationSupraspinatus
Extend, Add <90, Abd >90, Ext. Rotation, Horiz. Abd
Pos. Deltoid
Middle Deltoid
Flex, Add <90, Abd >90, ________ Rotation, Horiz. ________
Ant. Deltoid
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Muscular Motions Scapulothoracic
Abd, Inf-Upward Rotation, Depression, Sup-Downward Rotation, Elevation
Pectoralis Minor
Serratus Anterior
Levator Scapulae
Add, Downward Rotation, Elevation
Trapezius
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Muscular Motions of Multiple Joint Muscles
Biceps Brachii
Extend, Int. Rotation, Add, Horiz. Abd
Pectoralis Major
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OutlineAnatomyBiomechanicsProblems
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Reasons for Biomechanical Analysis
RehabilitationTherapy LoadsRepair Strengths
InjuryMotions That Transfer Higher LoadsInjury Mechanisms
Dislocation
Prosthetic DesignStress (Load) Analysis
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InjuriesBroken Bones
ClavicleScapulaHumerus
Impingement____________Biceps Tendon
Bursitis
DislocationSubluxation
Tendon Ruptures__________Biceps
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Impingement
CompartmentInflammationIncrease in PressureFeedback
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Dislocation______________ Most CommonSuperior Subluxation Difficult
AcromionCoracohumeral LigamentCoracoacromial Ligament
Rotator CuffProvides Dynamic StabilityProtects Inferior, Anterior, Posterior Displacements
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Rotator Cuff Repair
Suture AnchorBioscrewTackCyclic Loads to ___N (2/3 Max Contraction Force)45°
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Testing•Suture Anchor Good Overall•Tack Best for Good Cuff-Weak Bone•Screw Best for Strong Bone-Any Cuff
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Joint ReplacementLoosening
CementedUncemented
Prostheses DesignStress Shielding
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Troubles with Biomechanical Analysis
Mobility High Number of Degrees of Freedom
Muscles Large Number of Muscles Contributing
Different Contributions..
Angle of Elevation
Multiple MovementsArm Position (example: Biceps)
Abductor while humerus is Externally Rotated
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Multiple Motions of Single Muscle
Anterior Deltoid - Muscle Flexion/Internal RotationTeres Major - Muscle Extension/Internal Rotation
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Coupling - Forces Acting in Different Directions to Produce the Same Movement
Downward RotationRhomboids-Pectoralis Minor-Serratus Anterior (Superior)
Upward Rotation (figure)Elevation (Frontal)
A. Deltoid-Teres Minor-Infraspinatus
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Muscle Pair RatiosFlex:Extension ( )Abd:Add ( )Internal:External ( )Adduction-Extension-Flexion-Abduction-Internal Rotation-External Rotation
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Forces at the Shoulder (Innman et al., 1944)
90° AbductionDeltoid Extremity Weight (70% BW)GH Joint EW (90% BW)Rotator Cuff EW (85% BW)Load Bearing (Approximately 1BW)
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Forces at the Shoulder (Poppen et al., 1978)
Abduction in the Frontal Plane ElevationBent Arm Reduces Shoulder Force by
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Shoulder DynamicsFatigue and Injury (Working with Arm Elevated)
SupraspinatusTrapezius
Supraspinatus TendonitisNeck Pain (Trapezius Fatigue)Less Fatigue (Herberts, 1980)
A. Deltoid (45° and 90°)Supraspinatus (45°)Trapezius (45°)
had Highest Fatigue
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Simplified Joint Force1 MuscleSegment WeightVector Addition
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Joint Force and Stability
A B
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Moment (Hinrichs, 1981)Reference Line from Anthropometric DataAverage Limb Weight ( BW)Average Center of Mass DistanceF*d=Moment
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OutlineAnatomyBiomechanicsProblems
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Problem #1 (1-D) ΣM=0
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Problem #2 (2-D)ΣFx=0ΣFy=0ΣM=0
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Problem #3 (3-D)ΣFx=0ΣFy=0ΣFz=0ΣM=0