The document provides an overview of the biomechanics of the shoulder complex. It describes the structure including the glenohumeral joint, sternoclavicular joint, acromioclavicular joint, and scapulothoracic articulation. It details the kinematics of the shoulder including motions like flexion, abduction, and rotation. The stability mechanisms are discussed as well as the muscles involved in shoulder motions. Injuries are addressed relating to impingement and ligament laxity.

1. Biomechanics the Shoulder Complex
Dr. Abid Ullah PT
Lecturer FIMS
Abbottabad
Email:
dr.abidullahpt@yahoo.com

2. Objective
 At the end of this lecture, you must be able to
 To identify the structure of the shoulder girdle, including joint
types, articular space, and the surrounding tissues
 To describe joint motion occurring at the shoulder complex ,
including Osteokinematics and Arthrokinematics movements ,
muscle action, and factors checking shoulder motions
 To understand the stability mechanism of the shoulder complex
and the possible mechanism of injury
 To distinguish the three degree of freedom joint from the one or
two degree of freedom joint
 To understand the effect of the muscle synergies and the
influence of weakness or paralysis of one single muscle in
coupled muscle muscle motion

3. The Shoulder complex
 Function of shoulder complex
 Structure of shoulder complex
 Kinematic of shoulder complex
 Muscle at the shoulder complex
 Shoulder Stability
 Mechanism of injury at the shoulder

4. Function of shoulder complex
 To link the upper extremity to the trunk
 Dependent arm position
 Control of rotator cuff muscle
 To provide extension mobility of the arm in space
 To provide stability for elbow and hand skillful or
forceful movements

5. Joints at Shoulder Complex
 Glenohumeral joint ( shoulder joint)
 Sternoclavicular joint
 Acromioclavicular joint
 Scapulothoracic articulation :
 muscle-bone articulation

6. Classified by smith et al 1996
 Bony articulation
 Glenohumeral joint ( GH jt)
 Sternoclavicular joint (SC jt)
 Acromioclavicular joint (AC jt)
 Functional joints
 Scapulothoracic articulation
 Suprahumeral articulation (Subacromial articulation):
 The articulation b/w coracoacromial ligament and the humerus
 Bicipital groove : the groove b/w the greater & lesser tuberosity
of the humerus

7. Glenohumeral joint ( GH jt)
 Proximal component : Scapula
 Concave glenoid cavity covered with glenoid labrum
that is a fibrocartilage to deepen the glenoid cavity
 Distal component: Humerus
 Convex humeral head
 Retroversion of the humeral head about 30 deg
posterior to the frontal axis of the elbow joint
 Joint type : ball & socket

8.  Motion : convex on concave
 Shoulder flexion/extension with posterior/anterior glide
of the humeral head on the glenoid cavity
 Shoulder abduction/adduction with inferior/superior
glide of the humeral head on the glenoid cavity
 Shoulder internal/external rotation with posterior
/anterior glide of the humeral head on the glenoid cavity
 Shoulder horizontal abduction/adduction with
anterior/posterior glide on the humeral head on the
glenoid cavity

9. Cont…
 DOF=3
 Neutral Position : Anatomical Position
 Resting Position: 70 degree of shoulder abduction and
30 degree of flexion ( horizontal adduction)
 Closed packed position: 90 of shoulder abduction and
full external rotation

10. Sternoclavicular joint ( SC jt)
 Proximal component: Sternum
 Saddle-shaped sternal manubrum
 Distal component: Clavicle
 Saddle-shaped medial end of the clavicle
 Disk b/w 2 articular surfaces
 Joint type: Saddle joint
 Motion: Shoulder girdle motion
 Clavicle elevation/depression
 Clavicle protraction/depression
 Clavicle posterior rotation
 DOF=3

11. Cont…
 Note: Clavicle
 Convex forward medially & concave forward laterally
 Quadripedal animals do not have clavicle
 Isokinetic strength of shoulder flexion and abduction
decreases 50% if clavicle is removed

12. Acromioclavicular joint ( AC Joint)
 Proximal component:
 Convex lateral end of clavicle
 Distal component:
 Concave acromion process of the scapula
 Joint type: nearly plane joint/ synovial joint
 Motion: shoulder girdle motion
 Scapula wining: medial boarder of the scapula moves back
wards
 Scapular tipping: inferior angle of the scapula moves back
wards
 Scapular upward/downward rotation: inferior angle of the
scapula rotates upward/downwards
 DOF= 3

13. Acromioclavicular joint ( AC Joint)

14. Scapulothoracic articulation (ST)
 Proximal component: convex rib cage
 Distal component: concave anterior surface of the scapula
 Note: an articulation b/w bone & muscle; not a synovial
joint
 Motion: shoulder girdle motion; convex on concave
 Scapular elevation/depression: whole scapula moves upward
/downwards
 Scapular abduction/adduction: medial boarder of the scapula
moves away from/towards the spine
 scapular upward/downward rotation: inferior angle of the
scapula rotates upward/downwards
 DOF=3

15. Cont…

16. Functions of the ST articulation
 To provide movement base for the humerus
 To maintain length –tension relationship for the
deltoid muscle to function above 90 degree of arm
elevation
 To provide stability of the glenohumeral joint working
overhead
 To absorb the shock for forces applied to the
outstretched arm
 To permit push-up during crutch walking

17. Suprahumeral articulation
 Synonym: subacromial joint
 Coracoacromial arch: composed of the coracoacromial
ligament
 Supraspinatus tendon passing underneath this arch
 Not for joint stability
 Shoulder impingement occurs if the subacromial space is
insufficient
 Insufficient inferior glide of the humeral head during arm elevation
 Insufficient external rotation of the humerus during arm elevation
 Inflammation of the tendon of the supraspinatus
 Hypertrophy of the tendon of the supraspinatus
 Subacromial ( subdeltoid) bursa

18. Cont…

19. Bicipital groove
 Groove b/w greater & lesser tuberosities of the humerus
covered with the transverse humeral ligament
 Passing tendon of long head of biceps brachii
 Intra –articular but extra-synovial
 Plane of scapula
 the plane at the angle of 30 degree anterior to frontal plane
 Not parallel to the frontal plane
 Capsule in the loose packed position
 No impingement in the Suprahumeral joint if shoulder
motion occur in the plane of scapula

20. Cont…

21. Kinematic of shoulder complex
 Shoulder flexion/extension
 Joint involved
 Glenohumeral joint
 Sternoclavicular joint
 Acromioclavicular joint
 Plane of motion: sagittal plane
 Axis of rotation: transverse axis through the center of
the humeral head

22. Cont…
 Osteokinematic movements
 Range of motion
 Glenohumeral joint : 0-90 degree for shoulder flexion &
0-45 degree or 60 degree for shoulder extension
 Closed kinematic chain motion
 Pull-up
 Push-up
 Rowing
 Upper extremity cycling on an ergometer

23. Cont…
 Arthokinematic movements
 Posterolateral glide of the humeral head on the glenoid
cavity with shoulder flexion
 Anteromedial glide of the humeral head on the glenoid
cavity with shoulder extension
 Factors limiting shoulder flexion
 Inferior glenohumeral ligament
 Tightness of the posterior joint capsule
 Factors limiting shoulder extension
 Superior & middle glenohumeral ligament

24. Shoulder abduction & adduction
 Arm elevation = shoulder abduction or flexion
 Joint involved
 Glenohumeral joint
 Sternoclavicular joint
 Acromioclavicular joint
 Scapulothoracic articulation
 Plane of motion: frontal plane
 Axis of rotation
 GH joint: sagittal axis through the center of the humeral head
 SC joint: sagittal axis through the center of the medial end of
the clavicle

25. Cont…
 Osteokinematic movement
 Range of motion
 Total range: 0-165-170 degree
 GH joint: 0-120 degree of shoulder abduction
 0-60 degree with full internal rotation of humerus
 0-90 degree with full external rotation of humerus
 SC joint: 0-30 -45 degree
 Most occurring in 1st 90 degree of arm elevation

26. Cont…
 Arthokinematic movements
 Shoulder abduction
 Inferior glide of the humeral head on the glenoid cavity
 Inferior glide of the clavicle on the sternum in most people
 Factors limiting shoulder abduction:
 Inferior glenohumeral ligament
 Tightness of inferior joint capsule of the glenohumeral joint
 Tightness of costoclavicular & interclavicular ligament &
subclavicius muscle at the SC joint
 Factors limiting shoulder adduction:
 trunk

27. Shoulder internal/external rotation
 Joint involved
 GH joint
 SC joint
 AC joint
 ST articulation
 Plane of motion: Transverse plane
 Axis of rotation: vertical axis through the center of the
humeral head

28. Cont…
 Osteokinematic movements
 Range of motion ( ROM)
 Shoulder inter rotation: 0-70 degree as the arm at 90
degree of shoulder abduction & 90 degree elbow flexion
 Shoulder external rotation: 0-90 degree as the arm at 90
degree of shoulder abduction & 90 degree elbow flexion
 Note: if the elbow is extended, shoulder rotation
occurs simultaneously with forearm rotation

29. Cont…
 Arthrokinematic movements
 Posterolateral glide of the humeral head on the glenoid
cavity with shoulder internal rotation
 Anteromedial glide of the humeral head on the glenoid
cavity with shoulder external rotation
 Factors limiting shoulder internal rotation
 Posterior capsule
 Factors limiting shoulder external rotation
 Coracohumeral ligament
 3 glenohumeral ligament

30. Cont…

31. Shoulder horizontal abduction/adduction
 Synonym: horizontal extension/flexion
 Shoulder flexion/extension at 90 degree of shoulder
abduction
 Horizontal abduction: arm moves backward as the arm is at 90
degree of shoulder abduction
 Horizontal adduction: arm moves forward as the arm is at 90
degree of shoulder abduction
 Joint involved
 GH joint
 SC joint
 AC joint
 ST articulation

32. Cont…
 Plane of motion: transverse plane
 Axis of rotation: vertical axis through the center of the
humeral head
 Arthrokinematic movements
 Anteromedial glide of the humeral head on the glenoid
cavity with shoulder horizontal abduction
 Posterolateral glide of the humeral head on the glenoid
cavity with shoulder horizontal adduction

33. Frontal plane motion at shoulder girdle
 Shoulder girdle elevation
 Definition: ST joint elevation associated with SC elevation &
AC tipping
 Joint involved
 ST articulation
 SC joint
 AC joint
 Arthrokinematic movement
 Elevation of the scapula on the rib cage
 Inferior glide of the clavicle on the sternum in most people
 Limited by the costoclavicular & interclavicular ligament &
subclavicius muscle

34. Cont…
 Shoulder girdle depression
 Definition: ST joint depression associated with SC depression
 Joint involved
 ST articulation
 SC joint
 AC joint
 Range: 10-15 cm from maximum scapular elevated position
 Arthroinokinematic movements
 Depression of the scapula on the rib cage
 Superior glide of the clavicle in most people
 Limited by 1st rib

35. Transverse plane motion at shoulder girdle
 Protraction
 Definition: ST joint abduction associated with SC protraction
 Joint involved
 ST articulation
 SC joint
 Axis of rotation: vertical axis passing through the center of the
medial head of the clavicle
 Range
 0-15 degree
 Abduction of scapula : 13-15 cm
 Arthrokinematic movements
 Abduction of scapula
 Protraction of scapula
 Limited by posterior sternoclavicular & costoclavicular ligamints

36. Cont…
 Retraction
 Definition: ST joint adduction associated with Sc retraction
 Joint involved
 ST articulation
 SC joint
 Axis of rotation: vertical axis passing through the center of the
medial head of the clavicle
 Range: 0-15 degree
 Arthrokinematic movements
 Adduction of the scapula
 Retraction of the clavicle
 Limited by anterior Sternoclavicular ligament
 Total range: 25 degree totally

37. Circumduction motion at the SC joint
 A combination of elevation, protraction, depression &
retraction or in reverse sequence
 Tip of the shoulder ( acromion process of the scapula)
moves in a circle path

38. Cont…

39. Scapulothoracic rotation
 Upward rotation
 Definition: glenoid fossa facing upward with inferior
angle of scapula sliding laterally & anteriorlly
 Osteokinematic movements
 First 30 degree: elevation of the clavicle through the axis
at the base of the spine of scapula
 Last 30 degree: posterior rotation of the clavicle &
scapular rotation around AC joint

40. Cont…
 Downward rotation
 Definition: glenoid fossa facing downwards with
inferior angle of scapula sliding medially & posteriorlly

41. Transverse rotation of clavicle
 Axis of rotation: longitudinal axis of clavicle
 Total range: 40 degree
 Occurring after 90 degree of arm elevation due to
tightening of the coracoclavicular ligament
 Arm elevation limited to 110 degree of this posterior
rotation is not taken place

42. Muscle for glenohumeral (shoulder) motions
Motion Prime movers
Shoulder flexion Deltoid, anterior fiber of coracobrchialis, bicep brachii, long
head of pectoralis major, clavicular head
Shoulder
extension
Latissimus dorsi, teres major, tricep brachii, long head of
deltoid, posterior fiber
Shoulder
abduction
Deltoid, supraspinatus, bicep brachii; long head
Shoulder
adduction
Pectoralis major, latissimus dorsi, teres major, bicep brachi
long head, deltoid postrior fiber
Shoulder external
rotation
Infraspinatus, teres major, deltoid posterior fiber
Shoulder internal
rotation
Subscapularis, teres major, pectoralis major, latssimus dorsi,
deltoid anterior fiber

43. Muscles for Scapulothoracic ( shoulder girdle) motion
Motion Prim movers
Scapular elevation Upper trapezius, levator scapulae, romboid major,
romboid minor
Scapular depression Pectoralis minor, lower trapezius, latssimus dorsi,
subclavis
Scapular protraction Serratus anterior, pectoralis major, pectoralis minor
Scapular retraction Trapezius, romboid major, romboid minor
Scapular upward
rotation
Trapezius, serratus anterior
Scapular downward
rotation
Levator scapula, romboid major, romboid minor

44. Serratus anterior
 Origin: rib 1- 9
 Insertion: medial border of the scapula
 Motion: protraction and upward rotation

45. Rotator cuff
 Supraspinatus
 Infraspinatus
 Teres minor
 Subscapularis
 Abduct and rotate the humerus
 Act as glenohumeral stabilizer

46. Pectoralis minor
 Origin: rib 2-5
 Insertion: coracoid process of the scapula
 Depression & downward rotation
 Agonist
 Depressor
 Downward rotators
 Antagonist
 elevation + upward rotation

47. Shoulder complex stability
 Factors affecting stability of glenohumeral joint:
primarily depend on muscles & ligaments
 Bony configuration
 0-5 degree of superior inclination ( upward tilt) of the
glenoid cavity
 Shape of the cartilage
 Depend glenoid labrum

48. Cont…
 Tension of ligaments
 Superior glenohumeral ligament
 Middle glenohumeral ligament
 Inferior glenohumeral ligament
 Coracohumeral ligament

49. Cont…
 Muscular arrangement : rotator cuff
 Supraspinatus
 Infraspinatus
 Teres minor
 Subscapularis
 capsule

50. Mechanism of injury at the shoulder
 Direct stress
 Direct stress Ac joint separation
 Anterior stress anterioinferior dislocation of the
humeral head
 Repeated stress
 Repeated shoulder rotation motion as the shoulder is
placed at 90 degree of abduction Repeated tensile
stress on rotator cuff Rotator cuff tendinitis

51. Assignments
 What are the movements of the scapula?
 What is Scapular Elevation?
 What plane does elevation and depression occur in?
 Why is the Scapulothoracic joint not a true joint?
 What muscles upwardly rotate the scapula?
 What are the muscles that elevate the scapula?
 What muscles cause depression of scapula?
 What muscles move the scapula?