Biomechanics of shoulder complex

this is a ppt made usually for bachelor of physiotherapy students and contains the basic biomechanics of shoulder complex

1. BIOMECHANICS OF SHOULDER JOINT Debashree Roy

2. Introduction Shoulder joint (GH joint) has more mobility than stability. Only SC joint connects the components of shoulder joint to the axial skeleton. This puts greater demands on the muscles for securing the shoulder girdle on thorax during static and dynamic conditions (dynamic stabilization).

3. Components of shoulder complex Clavicle, humerus and scapula are linked with 3 interdependent linkages: SC joint, AC joint & GH joint. Additionally a functional joint called scapulothoracic joint ( ST joint) is considered as a part oh shoulder complex.

4. Components of shoulder complex

5. MOVEMENTS Elevation: Sagittal plane flexion and frontal plane abduction and all the motions in between.

6. STERNOCLAVICULAR JOINT

7. STERNOCLAVICULAR JOINT Movement of the clavicle at the SC joint inevitably produces movement of the scapula under conditions of normal function , because the scapula is attached to the lateral end of the clavicle. SC joint is a plane synovial joint , with 3 rotatory and 3 translatory degrees of freedom.

8. SC articulating surface: The SC articulation consists of two saddle-shaped surfaces, one at the sternal or medial end of the clavicle and one at the notch formed by the manubrium of the sternum and first costal cartilage. It is a plane synovial joint. The articulating surfaces are incongruent. The superior portion of the clavicle does not makes any contact with the manubrium , instead it serves as an attachment site for SC disk and interclavicular ligaments.

9. Sternoclavicular disk It is a fibrocartilaginous disk to increase the congruency b/w incongruent articular surfaces. Attachment: upper portion is attached to the postero -superior clavicle and the lower portion is attached to the manubrium and first costal cartilage. The disk diagonally transects the SC joint space and divides the joint into 2 separate cavities.

10. The disk is considered part of the manubrium in elevation/depression and thus the upper attachment of the disk serves as pivot point and the disk acts as the part of the clavicle in protraction/ retraction with lower attachment serving as pivot point. The axis of motions of SC joint elevation/depression and protraction/retraction is located lateral to the SC joint, on the costoclavicular ligament . The disk functions to absorb the medially directed force transmitted along the clavicle from its lateral end.

11. Sternoclavicular joint capsule and ligaments Sc joint is supported by fibrous capsule 3 ligaments : Sternoclavicular ligament Costoclavicular ligament Interclavicular ligaments ANTERIOR POSTERIOR ANTERIOR LAMINA POSTERIOR LAMINA

12. Sternoclavicular motions 3 rotatory degrees of freedom : Elevation/depression Protraction/retraction Anterior/posterior rotation of clavicle 3 degrees of translatory motion at the SC joint (very small in magnitude): Anterior/posterior Medial/lateral Superior/inferior

13. Elevation/depression of clavicle

14. Clavicular elevation= upto 48 degrees Passive clavicular depression= less than 15 degrees

15. Protraction/retraction of clavicle

16. protraction= 15-20 degrees Retraction= 20-30 degrees

17. Anterior and Posterior Rotation of the Clavicle

18. Posterior rotation= 50 degrees Anterior rotation= less than 10 degrees

19. Sternoclavicular stress tolerence Although the SC joint is considered incongruent, the joint does not undergo the degree of degenerative change common to the other joints of the shoulder complex. Strong force-dissipating structures such as the SC disk and the costoclavicular ligament minimize articular stresses and also prevent excessive intra- articular motion that might lead to subluxation or dislocation.

20. Acromioclavicular Joint

21. AC JOINT Plane synovial joint 3 rotational and 3 translational degrees of freedom The primary function of the AC joint is to allow the scapula additional range of rotation on the thorax and allow for adjustments of the scapula (tipping and internal/external rotation) outside the initial plane of the scapula in order to follow the changing shape of the thorax as arm movement occurs. In addition, the joint allows transmission of forces from the upper extremity to the clavicle.

22. AC articulating surface Incongruent surfaces Variation in inclination of articulating surface: flat, reciprocally concave-convex, or reversed (reciprocally convex-concave).

23. AC joint disk Through 2 years of age, the AC joint is actually a fibrocartilaginous union. With use of UE progressively, a joint space develops on each articulating surface that may leave a meniscoid fibrocartilage remnant within the joint.

24. AC joint capsule and ligaments Superior acromioclavicular ligament Inferior acromioclavicular ligament Coracoclavicular ligament TRAPEZOID (LATERAL) CONOID (MEDIAL)

25. The capsule of the AC joint is weak and cannot maintain integrity of the joint without reinforcement of the superior and inferior acromioclavicular and the coracoclavicular ligaments. Superior AC ligament is reinforced by aponeurotic extensions from deltoid and trapezius .

26. Trapezoid portion : oriented more horizontally. It resists posterior forces on distal clavicle Conoid portion : oriented more vertically. It resists superior and inferior forces Both limit upward rotation of scapula on AC joint. Prevents medial displacement of acromion on clavicle when leaning on 1 hand CC lig helps in coupling post clavicular rot with scapular upward rot during elevation of arm.

27. AC motions 3 rotatory motions: Internal/external rotation Anterior and posterior tipping Upward and downward rotation 3 translatory motions: Anterior/posterior Medial/lateral Superior/inferior

28. Axis and planes for AC joint motions

29. Internal/external rotation

30. While elevating the arm Protraction and retraction of the scapula require internal and external rotation, respectively, for the scapula to follow the convex thorax and orient the glenoid fossa with the plane of elevation.

31. Smaller values ( 20 to 35 degrees) have been reported during arm motions , although up to 40 to 60 degrees may be possible with full-range motions reaching forward and across the body.

32. Anterior and posterior tipping

33. While elevating the arm The scapula posteriorly tips on thorax as the scapula is upwardly rotating.

34. The magnitude of anterior/posterior tipping during elevation of arm is approx 30 degrees. Although in maximal flexion and extension, ant/post tipping can reach up to 40 degrees or more

35. Upward and downward rotation

36. Upward rotation=30 degrees Downward rotation=17 degrees

37. Acromioclavicular stress tolerence AC joint is susceptible to trauma and degenerative changes because of Smaller and incongruent surfaces. It is commonly found in 2 nd decade to 6 th decade of life.

38. Scapulo -thoracic joint

39. ST JOINT It is not a true anatomic joint. The functional ST joint is part of a true closed chain with the AC and SC joints and the thorax.

40. RESTING POSITION OF SCAPULA

41. Resting position of scapula 2 inches from midline b/w 2 nd and 7 th rib. Internally rot -30-45 degrees from coronal plane. Ant tipped -10-20degrees from frontal plane Upward rotated - 10-20 degrees from sagittal plane

42. The linkage of the scapula to the AC and SC joints, however, actually prevents scapular motions both from occurring in isolation and from occurring as true translatory motions. Eg . When the arm is abducted, scapula undergoes upward rotation, external rotation and posterior tipping (all movts in combination).

43. MOTIONS OF THE SCAPULA Upward rotation Elevation/depression Protraction/retraction Internal /external rotation

44. UPWARD ROTATION Approx. 60 degrees of upward rotation of the scapula on the thorax is typically available. Upward rotation of the scapula is produced by clavicular elevation and posterior rotation at the SC joint and by rotations at the AC joint .

45. ELEVATION/DEPRESSION Elevation and depression of the scapula are produced by elevation/depression of the clavicle at the SC joint and requires subtle adjustments in anterior/posterior tipping and internal/external rotation at the AC joint to maintain the scapula in contact with the thorax.

46. PROTRACTION/RETRACTION Protraction and retraction of the scapula are produced by protraction/retraction of the clavicle at the SC joint, and by rotations at the AC joint to produce internal rot & ant tipping.

47. Internal/external rotation Internal/external rotation of the scapula on the thorax should normally accompany protraction/ retraction of the clavicle at the SC joint. Internal rotation of the scapula on thorax which occurs only at the AC joint, will result in the prominence of the vertebral border of scapula. ( WINGING OF SCAPULA-suggestive of impaired neuromuscular control of ST muscles ) .

48. GLENO-HUMERAL JOINT

49. GH ARTICULATING SURFACE Scapula- Glenoid fossa is oriented/facing upwards and 6-7 degrees retroverted . The radius of curvature of the fossa is increased by articular cartilage that is thinner in the middle and thicker on the periphery, which improves congruence with the much larger radius of curvature of the humeral head.

50. Humerus - The head faces medially, superiorly, and posteriorly with regard to the shaft of the humerus and the humeral condyles . ANGLES: Angle of inclination=130-150 degrees Angle of torsion=30 degrees posteriorly

51. Angle of inclination Angle of torsion

52. Because of the internally rotated resting position of the scapula on the thorax, retroversion of the humeral head increases congruence of the GH joint. Reduced retroversion of humeral head ( anteversion )- increases ROM for internal rotation and decreases ROM for external rotation and has a tendency to produce anterior GH subluxation . Vice versa for increased retroversion of humeral head.

53. Subluxation of shoulder

54. GLENOID LABRUM Enhance the depth or curvature of the fossa by 50%. It is a redundant fold of dense fibrous connective tissue with little fibrocartilage . It is attached to glenohumeral ligament and long head of biceps brachii .

55. GH CAPSULE & LIGAMENTS GH Capsule laxity is required for large excursions of shoulder joint. But capsule gives less stability alone and its work has to be reinforced by GH ligaments.

56. GH ligament Superior Middle Inferior Coracohumeral lig Foramen of weitbrecht - area of weakness in the capsule.

57. Rotator interval capsule superior GH ligament, the superior capsule, and the coracohumeral ligament are interconnected structures that bridge the space between the supraspinatus and subscapularis muscle tendons- rotator interval capsule .

58. Inferior GH ligament complex Inferior GH ligament has 3 parts: Anterior bands Axillary pouch Posterior bands

59. Function of GH ligament

60. Coracoacromial arch

61. Coracoacromial arch Contents under coracoacromial arch: subacromial bursae , rotator cuff tendons and portion of long head of biceps brachii . Also called as supraspinatus outlet/ subacromial space Normally, it is 10 mm wide, but reduces to 5mm on elevation of arm. Repetitive overhead activity can cause painful impingement syndrome.

62. Bursae Subacromial Subdeltoid Subacromial bursae

63. Glenohumeral motions. MOTIONS ROM available Flexion 120 Extension 50 Abduction 90-120 Adduction External rotation 60 degrees of combined motions (arm at side) 120 degrees of combined motions ( arm at 90 degrees abducted) Internal rotation -

64. For complete range of abduction to occur, there must be 35-40 degrees of lateral rotation , for the clearance of greater tubercle under the Coracoacromial arch. MAXIMUM ABDUCTION IS FOUND TO OCCUR IN SCAPULAR PLANE , i.e 30-40 degrees anterior to frontal plane. This is due to lack of capsular tension in scapular plane.

65. Intra- articular Contribution to Glenohumeral Motions The convex humeral head is a substantially larger surface and may have a different radius of curvature than the shallow concave fossa . Given this incongruence, rotations of the joint around its three axes do not occur as pure spins but have changing centers of rotation and shifting contact patterns within the joint.

66. Without downward sliding of the articular surface of the humeral head, the humeral head will roll up the glenoid fossa and impinge upon the coracoacromial arch.

67. Slight superior translation of the center of the humeral head can still occur during humeral abduction despite inferior sliding of the head’s articular surface. (1-2mm)

68. Static Stabilization of the GH Joint in the Dependent Arm- UNLOADED ARM PASSIVE TENSION IN THE ROTATOR INTERVAL CAPSULE AIR-TIGHT CAPSULE PRODUCING NEGATIVE INTRAARTICULAR PRESSURE GLENOID INCLINATION -THERE IS SLIGHT UPWARD TILT OF GLENOID FOSSA EITHER DUE TO ANATOMICALLY OR DUE TO UPWARD ROTATION OF THE SCAPULA.

69. UNLOADED ARM

70. LOADED ARM-STATIC STABILIZATION SUPRASPINATUS ACTIVITY STARTS WHEN THE PASSIVE TENSION IN ROTATOR INTERVAL CAPSULE IS INSUFFICIENT AS IN LOADED ARM.

71. DYNAMIC STABILIZATION OF THE GH JOINT The Deltoid and Glenohumeral Stabilization The majority of the force of contraction of the deltoid causes the humerus and humeral head to translate superiorly; only a small proportion of force is applied perpendicular to the humerus and directly contributes to rotation (abduction) of the humerus . It also produces a shear force rather than a compressive force The deltoid cannot independently abduct (elevate) the arm. Another force or set of forces must be introduced to work synergistically with the deltoid for the deltoid to work effectively.

72. EFFECT OF DELTOID (ALONE) ON ABDUCTION

73. The Rotator Cuff and Glenohumeral Stabilization ROTATOR OR MUSCULOTENDINOUS CUFF MUSCLES ARE: Supraspinatus (S) Infraspinatus (I) Teres minor(T) Subscapularis (S)

74. The infraspinatus , teres minor, and subscapularis muscles individually or together have a similar line of pull. The rotatory component ( Fy ) compresses as well as rotates, and the translatory component ( Fx ) helps offset the superior translatory pull of the deltoid.

75. The Supraspinatus and Glenohumeral Stabilization The supraspinatus has a superiorly directed translatory component ( Fx ) and a rotatory component ( Fy ) that is more compressive than that of the other rotator cuff muscles and can independently abduct the humerus .

76. The Long Head of the BicepsBrachii and Glenohumeral Stabilization The long head of biceps may produce its effect by tightening the relatively loose superior labrum and transmitting increased tension to the superior and middle GH ligaments.

77. The long head of the biceps brachii , because of its position at the superior capsule and its connections to structures of the rotator interval capsule, is sometimes considered to be part of the reinforcing cuff of the GH joint. The biceps muscle is capable of contributing to the force of flexion and can, if the humerus is laterally rotated, contribute to the force of abduction and anterior stabilization.

78. Costs of Dynamic Stabilization of the Glenohumeral Joint Supraspinatus tendon tears Supraspinatus impingement in subacromial arch Rotator cuff tear AC joint degenerative changes Bicipital tendinitis Dislocation of shoulder

79. AC joint degenerative changes

80. Bicipital tendinitis

81. INTEGRATED FUNCTION OF SHOULDER COMPLEX

82. Scapulothoracic and Glenohumeral Contributions SCAPULAR UPWARD ROT = 60 DEGREES SCAPULA not only upwardly rotates but also posteriorly tips to 30 degrees. GLENO-HUMERAL CONTRIBUTION = 100 to 120 of flexion and 90 to 120 of abduction. TOTAL MOVEMENT IN ELEVATION= OF 150-180 DEGREES

83. The overall ratio of 2 of GH to 1 of ST motion during arm elevation is commonly used, and the combination of concomitant GH and ST motion most commonly referred to as scapulohumeral rhythm.

84. Sternoclavicular and Acromioclavicular Contributions

85. Sternoclavicular and Acromioclavicular Contributions The major shift in the axis of rotation( for scapular upward rotation) happens because the ST joint motion can occur only through a combination of motions at the SC and AC joints. When the axis of scapular upward rotation is near the root of the scapular spine , ST motion is primarily a function of SC joint motion; when the axis of scapular upward rotation is at the AC joint, AC joint motions predominate; when the axis of scapular upward rotation is in an intermediate position , both the SC and AC joints are contributing to ST motion.

86. 50 % of contribution from AC and SC joint is required to produce a total of 60 degrees of scapular upward rotation. Any additional degrees of upward rotation is accomplished by posterior rotation of clavicle.

87. Integrated movement during elevation

88. Upward Rotators of the Scapula The motions of the scapula are primarily produced by a balance of the forces between the trapezius and serratus anterior muscles through their attachments on the clavicle and the scapula.

89. TRAPEZIUS WITH SERRATUS Anterior -forms a force couple for scapular upward rotation INITIATION Of scapular rotation- upper trap + middle traps AT THE END RANGE = Lower traps

90. MUSCLES OF ELEVATION

91. DELTOID Scapular plane abduction- anterior and middle deltoid Posterior deltoid has smaller MA and thus less effective in frontal plane abduction. Maintenance of appropriate length-tension relationship of deltoid is dependent on scapular position/movement and stabilization. For example: when scapula cannot rotate , there is more shortening of deltoid and thus loss of tension, which causes elevation to upto 90 degrees only.

92. Supraspinatus Primary function is to produce abduction with deltoid muscle. It has a fairly constant MA throughout the range of motion of abduction Secondary function : acts as a ‘ steerer ’ of humeral head and helps to maintain stability of dependent arm.

93. Infraspinatus , teres minor and subscapularis These muscle function gradually increases from- 0-115 degrees of elevation after which (115-180 degrees) it dropped. In the initial range of elevation , these muscles ( infrasp and t.minor ) work to pull the humeral head down , and during the middle range, these muscles act to externally rotate for clearing greater tubercle under coracoacromial arch. Subscapularis helps as internal rot when arm is at side and during initial range With more abduction, its inter rot capacity decreases. Then it acts with other RC muscles to promote stability by compression.

94. UPPER AND LOWER TRAPEZIUS + SERRATUS ANTERIOR This force couple produces upward rotation of scapula. When the trapezius is intact and the serratus anterior muscle is paralyzed, active abduction of the arm can occur through its full range, although it is weakened. When the trapezius is paralyzed (even though the serratus anterior muscle may be intact), active abduction of the arm is both weakened and limited in range to 75, with remaining range occurring exclusively at the GH joint. Without the trapezius (with or without the serratus anterior muscle), the scapula rests in a downwardly rotated position as a result of the unopposed effect of gravity on the scapula.

95. Serratus anterior produces upward rotation, posterior tipping and external rotation of scapula , which is necessary for upward elevation of arm. The serratus is the primary stabilizer of the inferior angle and medial border of the scapula to the thorax.

96. How SA and trap work with deltoid?? The serratus anterior and trapezius muscles are prime movers for upward rotation of the scapula. These two muscles are also synergists for the deltoid during abduction at the GH joint. The trapezius and serratus anterior muscles, as upward scapular rotators, prevent the undesired downward rotatory movement of the scapula by the middle and posterior deltoid segments that are attached to the scapula. The trapezius and serratus anterior muscles maintain an optimal length-tension relationship with the deltoid and permit the deltoid to carry its heavier distal lever through full ROM.

97. Rhomboid It works eccentrically to control upward rotation of the scapula produced by the trapezius and the serratus anterior muscles. It adducts the scapula with lower traps to offset the lateral translation component of the serratus anterior muscle.

98. Muscles of Depression

99. Depression involves the forceful downward movement of the arm in relation to the trunk.

100. Latissimus Dorsi and Pectoral Muscle Function When the upper extremity is free to move in space , the latissimus dorsi muscle may produce adduction, extension , or medial rotation of the humerus . Through its attachment to both the scapula and humerus , the latissimus dorsi can also adduct and depress the scapula and shoulder complex. When the hand and/or forearm is fixed in weight-bearing , the latissimus dorsi muscle will pull its caudal attachment on the pelvis toward its cephalad attachment on the scapula and humerus . This results in lifting the body up as in a seated pushup .

101. Pectoralis major muscle Clavicular portion Sternal portion Abdominal portion Flexion of shoulder Depression of shoulder Depressor function is assisted by pectoralis minor

102. Teres Major and Rhomboid Muscle Function In order for the teres major muscle to extend the heavier humerus rather than upwardly rotate the lighter scapula , the synergy of the rhomboid muscles is necessary to stabilize the scapula.

103. REFERENCE: joint structure and function. Lavangie and Norkin , 4 th edition Thankyou