Bio Mechanics of the Shoulder

Biomechanics Biomechanics of of

the Shoulderthe Shoulder

Osteology

• The shoulder complex formed by SternumClavicleScapula Humerus

Osteology

ManubriumManubrium

BodyBody

Xyphoid Xyphoid processprocess

Osteology

Superior viewSuperior view

Inferior viewInferior view

Osteology

Anterior aspectAnterior aspect Posterior aspectPosterior aspect

Osteology

• Lateral border is thicker than medial– Because of all the

muscle attachments

http://www.bartleby.com/107/83.html

Osteology

• Anteriorly– Glenoid Cavity

•Shallow, oval-shaped depression

– Coracoid Process•Looks like a

bent finger

Osteology

• Posteriorly– Separated by

ribs by thin layers of muscle

– Spine•Strong, sharp

ridge

Osteology

Osteology

Osteology

Shoulder GirdleShoulder Girdle

Joints of the Shoulder

• Sternoclavicular jointSternoclavicular joint

• Acromioclavicular joint

• Coracoclavicular joint

• Scapulothoracic joint

• Glenohumeral joint

Sternoclavicular Joint

• Strong enough so that dislocation of joint is less common than fracture of clavicle

• Provides major axis of rotation for movement of clavicle and scapula

• Elevation: 60°. • 24-30° motion anterior, posterior, and

inferior• Helps position GH joint

Acromioclavicular Joint

• Irregular diarthrodial joint between the acromion process of the scapula and the distal clavicle.– Allows limited motions in all three

planes.

• Rotation occurs during arm elevation

• Close-packed position with humerus abducted to 90 degrees

Coracoclavicular Joint

• A syndesmosis with coracoid process of scapula– Bound to the inferior clavicle by the

coracoclavicular ligament.

• Permits little movement

Scapulothoracic jointScapulothoracic joint

• Not a true joint• The movement of the scapula on the

wall of the thoracic cage is critical to shoulder motion

• Contraction of the scapular muscles that attach the scapula to the axial skeleton, is critical in stabilizing the scapula and providing a base for joint function

Glenohumeral JointGlenohumeral Joint

• Ball and socket joint in which the Ball and socket joint in which the

head of the humerus articulates head of the humerus articulates

with the glenoid fossa of the scapulawith the glenoid fossa of the scapula

• Referred to as Referred to as thethe shoulder joint shoulder joint

Ligaments of the Sternoclavicular Joint

• Interclavicular ligament – Strengthens the capsule superiorly

• Costoclavicular ligament– Limits elevation of the pectoral girdle

Ligament of the Acromioclavicular Joint

• Acromioclavicular ligament – A fibrous band – This ligament strengthens the joint

superiorly

Ligaments of the Coracoclavicular Joint

• Coracoclavicular ligament – A strong pair of bands that unites the

coracoid process of the scapula to the clavicle

– Consists of two ligaments•Conoid ligament•Trapezoid

Ligaments of the Glenohumeral Joint

• Glenohumeral ligaments- Strengthen the anterior aspect of the

articular capsule - Three fibrous bands

Superior Glenohumeral ligamentTaut during external rotation and

plays a small role in the stability of the shoulder


• Glenohumeral ligamentsMiddle Glenohumeral ligament

Taut during external rotation and plays a small role in stability of the shoulder

Inferior Glenohumeral LigamentTaut during external rotation, and

plays a small role in stability of the shoulder


• Coracohumeral ligamentStrengthens the capsule superiorlyResists the pull of gravity and limits

external rotation of the shoulder• Transverse humeral ligament

Strengthens the capsule and bridges the gap between the greater and lesser tubercles of the humerus

keeps the biceps tendon in its groove during movements

Movements of the Shoulder Complex

• Movements of Movements of

the Scapulathe Scapula

– AbductionAbduction

(Protraction)(Protraction)

Movements of Scapula

Serratus Anterior


• Movements of

the Scapula

– Adduction

(Retraction)


Trapezius

Rhomboid major and minor

• Movements of

the Scapula

– Elevation



Levator Scapulae

Trapezius

Rhomboid major and minor

• Movements of

the Scapula

– Depression



Pectoralis minor

Serratus Anterior

Trapezius

• Movements of

the Scapula

– Upward

rotation



Serratus AnteriorTrapezius


• Movements of

the Scapula

– Downward

rotation


Levator Scapulae

Scapulohumeral RhythmScapulohumeral Rhythm

• A regular pattern of scapular A regular pattern of scapular

rotation that accompanies and rotation that accompanies and

facilitates humeral abductionfacilitates humeral abduction

• Scapulothoracic : glenohumeral Scapulothoracic : glenohumeral

joint movements = 1:2joint movements = 1:2

Composite Shoulder Girdle Movement




Shoulder Goniometry

• Flexion / Extension– 1800 / 500-600

• Abduction/Adduction– 1800 / 450-500

• Internal/External Rotation– 700-800 / 800-900

• Horizontal Abduction / Horizontal Adduction– 450 / 1200



• Movements of Glenohumeral joint– Flexion

Deltoid Pectoralis major

Coracobrachialis

Biceps brachii


• Movements of

Glenohumeral

joint

– Extension

Deltoid

Teres major

Triceps brachii

Latissimus dorsi

Abduction Adduction


Abduction

• Movements of

Glenohumeral

joint

– Abduction

DeltoidSupraspinatus

Adduction

• Movements of

Glenohumeral

joint

– Adduction

Pectoralis major

Teres major

Latissimus dorsi


External Rotation

• Movements of

Glenohumeral

joint

– Medial rotation

Infraspinatus Teres minor

Internal Rotation

• Movements of

Glenohumeral

joint

– Medial rotation

Internal Rotation

The body limits internal rotation - thus placing the arm behind the body increases the amount of internal rotation

Pectoralis majorTeres major

SubscapularisLatissimus dorsi


Biomechanics of GH Stability

• The normal shoulder constrains the humeral head to the center of the glenoid cavity throughout most of the arc of movement– Static restraints

– Dynamic restraints

Static restraints

• Glenoid labrum and articular surfaces

• Negative intra-articular pressure• Ligaments and capsule• Joint fluid adhesiveness

Dynamic restraints

• Rotator cuff muscles• Deltoid and biceps• Concavity compression

Rotator Cuff

Rotator Cuff

Stability Ratio

• Maximal displacing force in a given direction(perpendicular to glenoid center line) that can be stabilized by compressive load

• Affected by– Glenoid/labrum depth– rim lesions– Glenoid version– Dynamic stabilizer compromise

Load on the Shoulder

Load on the Shoulder

Documents

Bio Mechanics of the Shoulder