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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