Biomechanics of the Shoulder

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  • Topic: Scapula, Clavicle, Shoulder
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  • Published : April 1, 2013
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BIOMECHANICS OF THE SHOULDER

Hand and Upper Extremity Certification

SHOULDER BIOMECHANICS
* MOTION (Kinematics)
* STABILITY (Constraint)
* STRENGTH (Force Transmission)

OBJECTIVES
* -Introduction
* -Review of bone and joints
* -Scapulo-humeral rhythm
* -Review of muscles and force couples
* -Biomechanical applications

What does the shoulder do?

Shoulder Movement

SHOULDER VS. ARM ELEVATION
* Note difference in terminology

Normal Shoulder AROM

Activity and AROM (McGee)

Bones of the Shoulder

Clavicle
* Crank shaped strut
* Convex towards sternum/concave towards humerus
* Attaches shoulder to axial skeleton, force transmission to scapula, contributes to ROM * Palpation

Scapula
* Between T2 and T7
* Landmarks
* Primary function: muscle attachment
* Palpation: Acromion, Coracoid Process

Acromion Variations (Bigliani)

Glenoid Fossa

Plane of the Scapula
* Superior aspect 30◦- 45◦ a
* anterior to frontal plane
* Arm elevation in plane vs out of plane of scapula
* Try this motion!

Humerus
* Structures
* Tubercules (externally rotate humerus for grt. tubercule to clear acromion process and acromioclavicular ligament) * Try this!

Inclination and torsion
* Humeral head inclination=135◦
* Retroversion
* Angle of torsion=30◦

JOINTS OF THE SHOULDER
* Acromioclavicular
* Sternoclavicular
* Glenohumeral
* Scapulothoracic

Acromioclavicular Joint
* 3 degrees of freedom
* Elevation/depression
* Abduction/adduction
* Rotation of clavicle
* Ligaments:
* Coracoclavicular
* Acromioclavicular (surround capsule)

Trapezoid Ligament
* Medial stability during medial blow to shoulder facilitated by TRAPEZOID ligament

Conoid Ligament
* Arm elevation: initially clavicle and scapula in upward rotation together. * Scapula continues to elevate upwards and CONOID tightens * Clavicle becomes pulled in upwards rotation

A-C Separation

Sternoclavicular Joint
* Connects upper limb and axial skeleton
* 3 degrees of freedom:
* Elevation/depression, rotation, protraction/retraction * Ligaments:
* Anterior/posterior
* Interclavicular
* Costoclavicular
* Intraarticular disc

Sternoclavicular Joint
* Rotation of the sternoclavicular joint about an axis causes the head and opposite end of clavicle to move in opposite directions (seesaw)

Scapulothoracic joint
* No true articulations!
* 3 rotations, 2 translations
* Elevation and depression
* Abduction-adduction
* Upward-downward rotation
* Internal-external rotation
* Scapular tilt

Scapulothoracic “Joint”
* 5 ESSENTIAL FUNCTIONS
* 1) Increase ROM of shoulder to enhance reach
* 2) Maintain favourable length-tension relationship for the deltoid to function ›90◦ * 3) Maintain G-H stability for overhead work
* 4) Shock absorption
* 5) Permits elevation of body (eg. push-up)

Shoulder Girdle
* Clavicle
* Scapula
* Manubrium of sternum

Shoulder Girdle Elevation-Depression (Shoulder Shrug)
* Movement of clavicle at sternoclavicular joint
* Elevation: 50◦
* Depression: 10◦
* Upward/downward slide of scapula

Shoulder Girdle Protraction/Retraction
* Protaction: lateral end of clavicle and scapula move away from rib cage and scapular abduction * Retraction: lateral end of clavicle and scapula move posteriorly and scapular adduction * Sternoclavicular ROM: 30◦-60◦

Shoulder Girdle Upward/Downward Rotation
* Upward: glenoid fossa moves in superior direction
* Downward: glenoid fossa moves in inferior direction
* Total upward-downward ROM=60◦

Scapular Tilt
* Anterior: superior border of scapula tips forward
* Posterior: superior border of scapula...
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