1. SHOULDER COMPLEX
Dr. Michael P. Gillespie

2. ARTICULATIONS OF THE SHOULDER
Four articulations of the shoulder exist involving the sternum, clavicle, ribs, scapula and humerus.
The series of joints of the shoulder complex allow for extensive range of motion to the upper extremity.
This extensive range of motion allows us to reach and manipulate objects.
Dr. Michael P. Gillespie

3. JOINTS OF THE SHOULDER COMPLEX
Dr. Michael P. Gillespie
FIGURE 5-1.   The joints of the right shoulder complex.

4. MUSCLE INTERACTIONS
Muscles of the shoulder complex rarely act isolation, but rather work in “teams” to produce highly coordinated movements.
These movements are expressed over multiple joints.
The coordinated actions of multiple muscles allows for great versatility, control and range of motion.
Paralysis or weakness of any single muscle often disrupts the entire kinematic sequencing of the entire shoulder complex.
Dr. Michael P. Gillespie

5. OSTEOLOGY Sternum Clavicle Scapula Proximal-to-Mid Humerus
Dr. Michael P. Gillespie

6. OSTEOLOGIC FEATURES OF THE STERNUM
Manubrium
Pair of oval-shaped clavicular facets, which articulate with the clavicles.
Costal facets – attachment for first two ribs.
Jugular notch – superior aspect
Body
Xiphoid Process
Dr. Michael P. Gillespie

7. STERNUM: ANTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 5-2.   An anterior view of the sternum with left clavicle and ribs removed. The right side shows the first seven ribs and clavicle. The dashed line around the clavicular facet shows the attachments of the capsule at the sternoclavicular joint. Proximal attachments of muscle are shown in red.

8. OSTEOLOGIC FEATURES OF THE CLAVICLE
Shaft
Sternal end
Costal facet
Costal tuberosity
Acromial end
Acromial facet
Conoid tubercle
Trapezoid line
Dr. Michael P. Gillespie

9. CLAVICLE: SUPERIOR AND INFERIOR SURFACES
Dr. Michael P. Gillespie
FIGURE 5-3.   The superior and inferior surfaces of the right clavicle. The dashed line around the ends of the clavicle show attachments of the joint capsule. Proximal attachments of muscles are shown in red, distal attachments in gray.

10. OSTEOLOGIC FEATURES OF THE SCAPULA
Angles: Inferior, superior, and lateral
Medial or vertebral border
Lateral or axillary border
Superior border
Supraspinatous fossa
Infraspinatous fossa
Spine
Root of the spine
Acromion
Clavicular facet
Glenoid fossa
Supraglenoid and infraglenoid tubercles
Coracoid process
Subscapular fossa
Dr. Michael P. Gillespie

11. SCAPULA: POSTERIOR & ANTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 5-5A, 5-5-B.   Posterior (A) and anterior (B) surfaces of the right scapula. Proximal attachments of muscles are shown in red, distal attachments in gray. The dashed lines show the capsular attachments around the glenohumeral joint.

12. OSTEOLOGIC FEATURES OF THE PROXIMAL-TO-MID HUMERUS
Head of the humerus
Anatomic neck
Lesser tubercle and crest
Greater tubercle and crest
Upper, middle, and lower facets on the greater tubercle
Intertubercular (bicipital) groove
Deltoid tuberosity
Radial (spiral) groove
Dr. Michael P. Gillespie

13. HUMERUS: ANTERIOR & SUPERIOR VIEWS
Dr. Michael P. Gillespie
FIGURE 5-7A,B.   Anterior (A) and superior (B) aspects of the right humerus. The dashed line in A shows the capsular attachments around the glenohumeral joint. Distal attachment of muscles is shown in gray.

14. FOUR JOINTS WITHIN THE SHOULDER COMPLEX
Sternoclavicular
Acromioclavicular
Scapulothoracic
Glenohumeral
Dr. Michael P. Gillespie

15. ARTHROLOGY OF THE SHOULDER COMPLEX
The most proximal articulation within the shoulder complex is the sternoclavicular joint.
The clavicle functions as a mechanical strut holding the scapula at a relatively fixed distance from the trunk.
The acromioclavicular joint attaches the scapula to the clavicle.
The anterior surface of the scapula rests against the posterior-lateral surface of the thorax, forming the scapulothoracic joint. This is not a true anatomic joint. It is an interface between bones.
The scapula serves as a base of operation for the glenohumeral joint. The glenohumeral joint is the most distal and mobile link of the complex.
“Shoulder movement” describes the combined motions at the glenohumeral and scapulothoracic joints.
Dr. Michael P. Gillespie

16. PRIMARY MOVEMENTS OF THE SCAPULOTHORACIC JOINT
Elevation
Depression
Protraction
Retraction
Upward Rotation
Downward Rotation
Dr. Michael P. Gillespie

17. ELEVATION & DEPRESSION OF THE SCAPULOTHORACIC JOINT
Dr. Michael P. Gillespie
FIGURE 5-10A.   Motions of the right scapulothoracic joint. A, Elevation and depression. B, Protraction and retraction. C, Upward and downward rotation.

18. PROTRACTION & RETRACTION OF THE SCAPULOTHORACIC JOINT
Dr. Michael P. Gillespie
FIGURE 5-10B.   Motions of the right scapulothoracic joint. A, Elevation and depression. B, Protraction and retraction. C, Upward and downward rotation.

19. UPWARD ROTATION & DOWNWARD ROTATION OF THE SCAPULOTHORACIC JOINT
Dr. Michael P. Gillespie
FIGURE 5-10C.   Motions of the right scapulothoracic joint. A, Elevation and depression. B, Protraction and retraction. C, Upward and downward rotation.

20. STERNOCLAVICULAR JOINT: GENERAL FEATURES
The SC joint functions as the basilar joint of the entire upper extremity and links the appendicular skeleton to the axial skeleton.
The joint must be firmly attached, yet allow considerable range of movement.
Dr. Michael P. Gillespie

21. TISSUES THAT STABILIZE THE STERNOCLAVICULAR JOINT
Anterior and posterior sternoclavicular ligaments
Interclavicular ligament
Costoclavicular ligament
Articular disc
Sternocleidomastoid, sternothyroid, sternohyoid, and subclavius muscles
Dr. Michael P. Gillespie

22. KINEMATICS OF THE STERNOCLAVICULAR JOINT
Osteokinematics of the SC joint involve rotation in all three degrees of freedom.
Elevation & Depression
Protraction & Retraction
Axial (Longitudinal) Rotation of the Clavicle
Dr. Michael P. Gillespie

23. OSTEOKINEMATICS OF THE STERNOCLAVICULAR JOINT
Dr. Michael P. Gillespie
FIGURE 5-13.   The osteokinematics of the right sternoclavicular joint. The motions are elevation and depression in a near frontal plane (purple), protraction and retraction in a near horizontal plane (blue), and posterior clavicular rotation in a near sagittal plane (green). The vertical and anterior-posterior axes of rotation are color-coded with the corresponding planes of movement. The longitudinal axis is indicated by the dashed green line.

24. ACROMIOCLAVICULAR JOINT: GENERAL FEATURES
The AC joint is the articulation between the lateral end of the clavicle and the acromion of the scapula.
An articular disc is present in most AC joints.
The joint has an articular capsule and significant ligament support.
Dr. Michael P. Gillespie

25. TISSUES THAT STABILIZE THE ACROMIOCLAVICULAR JOINT
Superior and inferior acromioclavicular joint ligaments
Costoclavicular ligament
Articular disc (when present)
Deltoid and upper trapezius muscles
Dr. Michael P. Gillespie

26. KINEMATICS OF THE ACROMIOCLAVICULAR JOINT
The motions of the AC joint are described by the movement of the scapula relative to the lateral end of the clavicle.
Upward & Downward Rotation
Horizontal & Sagittal Plane “Rotational Adjustments” at the AC joint
Dr. Michael P. Gillespie

27. OSTEOKINEMATICS OF THE ACROMIOCLAVICULAR JOINT
Dr. Michael P. Gillespie
FIGURE 5-19A.   A, Posterior view showing the osteokinematics of the right acromioclavicular (AC) joint. The primary motions of upward and downward rotation are shown in purple. Horizontal and sagittal plane adjustments, considered as secondary motions, are shown in blue and green, respectively. Note that each plane of movement is color-coded with a corresponding axis of rotation.

28. OSTEOKINEMATICS OF THE ACROMIOCLAVICULAR JOINT
Dr. Michael P. Gillespie
FIGURE 5-19B, C.   Images B and C show examples of rotational adjustments at the AC joint: internal rotation during scapulothoracic protraction (B), and anterior tilting during scapulothoracic elevation (C).

29. ACROMIOCLAVICULAR JOINT DISLOCATION
The AC joint is inherently susceptible to dislocation due to the sloped nature of the articulation and the high probability of receiving large shearing forces.
Falling and striking the tip of the shoulder abruptly against the ground would produce such a shearing force.
Dr. Michael P. Gillespie
FIGURE 5-18.   An anterior view of the shoulder striking the ground with the force of the impact directed at the acromion. The resulting shear force at the acromioclavicular (AC) joint is depicted by red arrows. Note the increased tension and partial tearing of the AC joint capsule and coracoclavicular ligament.

30. SCAPULOTHORACIC JOINT
The scapulothroacic Joint is not a true joint, but rather a point of contact between the anterior surface of the scapula and the posterior-lateral wall of the thorax.
The two surfaces do not make direct contact. They are separated by muscles such as the subscapularis, serratus anterior, and erector spinae.
An audible click during scapular movements may indicate abnormal contact within the articulation.
Dr. Michael P. Gillespie

31. KINEMATICS OF THE SCAPULOTHORACIC JOINT
The movements at the scapulothoracic joint are a result of cooperation between the SC and the AC joints.
Elevation & Depression
Protraction & Retraction
Upward & Downward Rotation
Dr. Michael P. Gillespie

32. SCAPULOTHORACIC ELEVATION
Dr. Michael P. Gillespie
FIGURE 5-20.   A, Scapulothoracic elevation shown as a summation of B (elevation at the sternoclavicular joint) and C (downward rotation at the acromioclavicular joint).

33. SCAPULOTHORACIC PROTRACTION
Dr. Michael P. Gillespie
FIGURE 5-21.   A, Scapulothoracic protraction shown as a summation of B (protraction at the sternoclavicular joint) and C (slight internal rotation at the acromioclavicular joint).

34. SCAPULOTHORACIC UPWARD ROTATION
Dr. Michael P. Gillespie
FIGURE 5-22.   A, Scapulothoracic upward rotation shown as a summation of B (elevation at the sternoclavicular joint) and C (upward rotation at the acromioclavicular joint).

35. FUNCTIONAL IMPORTANCE OF UPWARD ROTATION
Many functional activities require us to raise the arm fully overhead.
The upward rotation of the scapula accounts for nearly 1/3 of the 180 degrees of shoulder abduction or flexion.
Functions
The upwardly rotated scapula projects the glenoid fossa upward and anterior-laterally, providing a structural base to maximize upward and lateral reach.
The upwardly rotated scapula preserves the optimal length-tension relationship of the abductor muscles of the glenohumeral joint (middle deltoid & supraspinatous).
The upwardly rotated scapula helps maintain the volume within the subacromial space. A reduced subacromial space can lead to painful and damaging impingement of the supraspinatus tendon and subacromial bursa).
Dr. Michael P. Gillespie

36. GLENOHUMERAL JOINT: GENERAL FEATURES
The GH joint is the articulation formed between the large convex head of the humerus and the shallow concavity of the glenoid fossa.
It operates in conjunction with the moving scapula to produce an extensive range of motion of the shoulder.
In anatomic position, the articular surface of the glenoid fossa is directed anterior-laterally in the scapular plane.
In anatomic position, the humeral head is directed medially and superiorly, as well as posteriorly.
This orientation places the head of the humerus directly against the face of the glenoid fossa.
Dr. Michael P. Gillespie

37. GLENOHUMERAL JOINT: ANTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 5-23.   Anterior view of a frontal section through the right glenohumeral joint. Note the fibrous capsule, synovial membrane (blue), and the long head of the biceps tendon. The axillary pouch is shown as a recess in the inferior capsule.

38. “LOOSE FIT” OF THE GLENOHUMERAL JOINT & INSTABILITY
Several features of the glenohumeral joint contribute to a design that favors mobility at the expense of stability.
The articular surface of the glenoid fossa covers only about 1/3 of the articular surface of the humeral head.
The longitudinal diameter of the humeral head is about 1.9 times larger than the longitudinal diamter of the glenoid fossa.
The transverse diameter of the humeral head is about 2.3 times larger than the opposing transverse diameter of the glenoid fossa.
The surrounding muscles and ligaments maintain the mechanical integrity of the joint.
A condition of excessive laxity or “joint play” associated with large translations of the proximal humerus relative to the glenoid is often referred to as shoulder instability.
Subluxation – incomplete separation of articular surfaces often followed by spontaneous realignment
Dislocation – complete separation of articular surfaces without spontaneous realignment
Dr. Michael P. Gillespie

39. “LOOSE FIT” IN GLENOHUMERAL JOINT
Dr. Michael P. Gillespie
FIGURE 5-24.   Side view of right glenohumeral joint with the joint opened up to expose the articular surfaces. Note the extent of the subacromial space under the coracoacromial arch. Normally this space is filled with the supraspinatus muscle and its tendon, and the subacromial bursa. The longitudinal and horizontal diameters are illustrated on both articular surfaces.

40. GLENOHUMERAL JOINT STABILITY
A combination of passive and active mechanisms achieve GH joint stability.
Active mechanisms
Forces produced by muscle
Embracing nature of the rotator cuff
Passive mechanisms
Forces other than activated muscle
1. restraint provided by capsule, ligaments, glenoid labrum, and tendons
2. mechanical support predicated on scapulothoracic posture
3. negative intracapsular pressure
Dr. Michael P. Gillespie

41. ROTATOR CUFF MUSCLES & LONG HEAD OF BICEPS BRACHII
The glenohumeral joint receives significant structural reinforcement from the four rotator cuff muscles.
The subscapularis is the thickest of these muscles and lies just anterior to the scapula.
The supraspinatus, infraspinatus, and teres minor lie superior and posterior to the capsule.
These four muscles form a cuff that protects and actively stabilizes the GH joint, especially during dynamic activities.
The belly of these muscles lies close to the joint.
The tendons of these muscle blend into the capsule.
The tendon of the long head of the biceps reinforces the rotator interval (between supraspinatus and subscapularis).
Dr. Michael P. Gillespie

42. ROTATOR CUFF MUSCLE SUPPORT
Dr. Michael P. Gillespie
FIGURE 5-26.   Lateral aspect of the internal surface of the right glenohumeral joint. The humerus has been removed to expose the capsular ligaments and the glenoid fossa. Note the prominent coracoacromial arch and underlying subacromial bursa (blue). The four rotator cuff muscles are shown in red.

43. TISSUES THAT REINFORCE OR DEEPEN THE GLENOHUMERAL JOINT
Joint capsule and associated capsular ligaments
Coracohumeral ligament
Rotator cuff muscles (subscapularis, supraspinatus, infraspinatus, and teres minor)
Long head of biceps brachii
Glenoid labrum
Dr. Michael P. Gillespie

44. KINEMATICS OF THE GLENOHUMERAL JOINT
Movement occurs in all three degrees of freedom.
Abduction & Adduction
Flexion & Extension
Internal & External Rotation
Dr. Michael P. Gillespie

45. OSTEOKINEMATICS OF THE GLENOHUMERAL JOINT
Dr. Michael P. Gillespie
FIGURE 5-30.   The osteokinematics of the glenohumeral joint includes abduction and adduction (purple), flexion and extension (green), and internal and external rotation (blue). Note that each axis of rotation is color-coded with its corresponding plane of movement.

46. GLENOID LABRUM: VULNERABLE TO INJURY
The rim of the glenoid fossa is encircled by a fibrocartilage ring, or lip, known as the glenoid labrum.
It deepens the concavity of the fossa and increases the contact area with the humeral head to help stabilize the joint.
The superior part of the glenoid labrum is only loosely attached.
50% of the fibers of the tendon of the long head of the biceps are direct extensions of the superior glenoid labrum.
Large or repetitive forces within the biceps tendon can detach the superior labrum (near its 12 o’clock position).
Dr. Michael P. Gillespie

47. GLENOHUMERAL JOINT: ACTIVE ABDUCTION
Dr. Michael P. Gillespie
FIGURE 5-31.   The arthrokinematics of the right glenohumeral joint during active abduction. The supraspinatus is shown contracting to direct the superior roll of the humeral head. The taut inferior capsular ligament (ICL) is shown supporting the head of the humerus like a hammock. Note that the superior capsular ligament (SCL) remains relatively taut because of the pull from the attached contracting supraspinatus. Stretched tissues are depicted as long black arrows.

48. GLENOHUMERAL JOINT: FLEXION
Dr. Michael P. Gillespie
FIGURE 5-33.   Side view of flexion in the near sagittal plane of the right glenohumeral joint. A point on the head of the humerus is shown spinning around a point on the glenoid fossa. Stretched structures are shown as long thin arrows. PC, posterior capsule; ICL, inferior capsular ligament; CHL, coracohumeral ligament.

49. KINEMATIC RELATIONSHIPS OF THE GLENOHUMERAL JOINT
Osteokinematics
Plane of Motion /
Axis of Rotation
Arthrokinematics
Abduction & adduction
Near frontal plane / near anterior-posterior axis of rotation
Roll and slide along joint’s longitudinal diameter
Internal & external rotation
Horizontal plane / vertical axis of rotation
Roll and slide along joint’s transverse diameter
Flexion & Extension, internal & external rotation (in 90 degrees of abduction)
Near sagittal plane / near medial-lateral axis of rotation
Primarily a spin between humeral head and glenoid fossa
Dr. Michael P. Gillespie

50. SCAPULOHUMERAL RHYTHM
“Scapulohumeral rhythm” describes the kinematic relationship between glenohumeral abduction and scapulothoracic upward rotation.
After about 30 degrees of abduction, the rhythm is remarkably constant.
For every 3 degrees of shoulder abduction, 2 degrees occur by GH joint abduction and 1 degree occurs by scapulothoracic upward rotation.
A full arc of 180 degrees of abduction is the result of a simultaneous 120 degrees of GH joint abduction and 60 degrees of scapulothoracic upward rotation.
Dr. Michael P. Gillespie

51. SCAPULOHUMERAL RHYTHM
Dr. Michael P. Gillespie
FIGURE 5-35.   Posterior view of the right shoulder complex after the arm has abducted 180 degrees. The 60 degrees of scapulothoracic joint upward rotation and the 120 degrees of glenohumeral (GH) joint abduction are shaded in purple. Additional inserts contained in the boxes depict superior and lateral views of selected kinematics of the clavicle and scapula, respectively. All numeric values are chosen from a wide range of estimates cited across multiple literature sources. Actual kinematic values vary considerably among persons and studies.

52. SHOULDER ABDUCTION IN THE FRONTAL PLANE VERSUS THE SCAPULAR PLANE
Shoulder abduction in the frontal plane is often used as a representative motion to evaluate overall shoulder function; however, this motion is not very natural.
Abducting the shoulder in the scapular plane (about 35 degrees anterior to the frontal plane) is a more natural movement and generally allows greater elevation of the humerus than in the frontal plane.
Dr. Michael P. Gillespie

53. ABDUCTION: FRONTAL VS. SCAPULAR
Dr. Michael P. Gillespie
FIGURE 5-38A, B.   Side view of the right glenohumeral joint comparing abduction of the humerus in A, the true frontal plane and B, the scapular plane. In both A and B, the glenoid fossa is oriented in the scapular plane. The relative low and high points of the coracoacromial arch are also depicted. The line of force of the supraspinatus is shown in B, coursing under the coracoacromial arch.

54. INNERVATION OF MUSCLES & JOINTS OF THE SHOULDER COMPLEX
Brachial Plexus
Innervation of Muscle
Innervation to the Joints
Dr. Michael P. Gillespie

55. BRACHIAL PLEXUS Dr. Michael P. Gillespie
FIGURE 5-39.   The brachial plexus.

56. NERVES THAT FLOW FROM THE BRACHIAL PLEXUS AND INNERVATE THE SHOULDER
Primary Nerve Root(s)
Muscles Supplied
Axillary
C5, C6
Deltoid, teres mino
Thoracodorsal (middle subscapular)
C6, C7, C8
Latissimus dorsi
Upper subscapular
Subscapularis (upper fibers)
Lower subscapular
Subscapularis (lower fibers), teres major
Lateral pectoral
C5, C6, C7
Pectoralis major and occasionally pectoralis minor
Dr. Michael P. Gillespie

57. NERVES THAT FLOW FROM THE BRACHIAL PLEXUS AND INNERVATE THE SHOULDER
Primary Nerve Root(s)
Muscles Supplied
Medial pectoral
C8, T1
Pectoralis major (sternocostal head), pectoralis minor
Suprascapular
C5, C6
Supraspinatus, infraspinatus
Subclavian
subclavius
Dorsal scapular C5
Rhomboid major & minor, levator scapula*
Long thoracic
C5, C6, C7
Serratus anterior
Dr. Michael P. Gillespie
* Also innervated by C3 & C4 nerve roots from cervical plexus

58. PRIMARY MUSCLES ACTING AT THE SCAPULOTHORACIC JOINT
Elevators
Upper trapezius
Levator scapulae
Rhomboids
Depressors
Lower trapezius
Latissimus dorsi
Pectoralis major
Subclavius
Dr. Michael P. Gillespie

59. PRIMARY MUSCLES ACTING AT THE SCAPULOTHORACIC JOINT
Protractors
Serratus anterior
Retractors
Middle trapezius
Rhomboids
Lower trapezius
Dr. Michael P. Gillespie

60. PRIMARY MUSCLES ACTING AT THE SCAPULOTHORACIC JOINT
Upward Rotators
Serratus anterior
Upper and lower trapezius
Downward Rotators
Rhomboids
Pectoralis minor
Dr. Michael P. Gillespie

61. ELEVATORS OF THE SCAPULOTHORACIC JOINT
Dr. Michael P. Gillespie
FIGURE 5-40.   Posterior view showing the upper trapezius, levator scapula, rhomboid major, and rhomboid minor as elevators of the scapulothoracic joint. Parts of the middle deltoid, the posterior deltoid, and the middle and lower trapezius are also illustrated.

62. DEPRESSORS OF THE SCAPULOTHORACIC JOINT
Dr. Michael P. Gillespie
FIGURE 5-42A, B.   A, A posterior view of the lower trapezius and the latissimus dorsi depressing the scapulothoracic joint. These muscles are pulling down against the resistance provided by the spring mechanism. B, An anterior view of the pectoralis minor and subclavius during the same activity described in A.

63. PROTRACTION OF THE SCAPULOTHORACIC JOINT
Dr. Michael P. Gillespie
FIGURE 5-44A, B.   The right serratus anterior muscle. A, This expansive muscle passes anterior to the scapula to attach along the entire length of its medial border. The muscle’s line of force is shown protracting the scapula and arm in a forward pushing or reaching motion. The fibers that attach near the inferior angle may assist with scapulothoracic depression. B, A superior view of the right shoulder girdle showing the protraction torque produced by the serratus anterior. The strength of the protraction torque is primarily the result of the muscle force multiplied by the internal moment arm (IMA) originating at the vertical axis of rotation at the sternoclavicular joint. The vertical axis of rotation is also shown at the acromioclavicular joint.

64. RETRACTION OF THE SCAPULOTHORACIC JOINT
Dr. Michael P. Gillespie
FIGURE 5-45.   Posterior view of the middle trapezius, lower trapezius, and rhomboids cooperating to retract the scapulothoracic joint. The dashed line of force of both the rhomboid and lower trapezius combines to yield a single retraction force, shown by the thin straight arrow.

65. MUSCLES PRIMARILY RESPONSIBLE FOR ELEVATION OF THE ARM
The term “elevation” of the arm describes the active movement of bringing the arm overhead without specifying the exact plane of motion.
Glenohumeral Joint Muscles
Anterior and middle deltoid
Supraspinatous
Coracobrachialis
Biceps (long head)
Scapulothoracic Joint Muscles
Serratus anterior
Trapezius
Rotator Cuff Muscles
Supraspinatus
Infraspinatus
Teres minor
Subscapularis
Dr. Michael P. Gillespie

66. FUNCTION OF THE ROTATOR CUFF MUSCLES IN ABDUCTION AT THE GLENOHUMERAL JOINT
Supraspinatus
Drives the superior roll of the humeral head
Compress the humeral head firmly against the glenoid fossa
Creates a semirigid spacer above the humeral head, restricting excessive superior translation of the humerus
Infraspinatus, Teres Minor, and Subscapularis
Exert a depression force on the humeral head
Infraspinatus and Teres Minor
Externally rotate the humerus
Dr. Michael P. Gillespie

67. SHOULDER ADDUCTION & EXTENSION
Dr. Michael P. Gillespie
FIGURE 5-55.   Anterior view of the right pectoralis major showing the adduction and extension function of the sternocostal head. The clavicular head of the pectoralis major is also shown.

68. SCAPULOTHORACIC DOWNWARD ROTATION & GLENOHUMERAL ADDUCTION
Dr. Michael P. Gillespie
FIGURE 5-57.   Posterior view of a shoulder showing the muscular interaction between the scapulothoracic downward rotators and the glenohumeral adductors (and extensors) of the right shoulder. For clarity, the long head of the triceps is not shown. The teres major is shown with its internal moment arm (dark line) extending from the glenohumeral joint. The rhomboids are shown with the internal moment arm extending from the scapula’s axis. IF, infraspinatus and teres minor; LD, latissimus dorsi; PD, posterior deltoid; RB, rhomboids; TM, teres major.

69. INTERNAL ROTATION OF THE SHOULDER
Dr. Michael P. Gillespie
FIGURE 5-58.   Superior view of the right shoulder showing the group action of the internal rotators around the glenohumeral joint’s vertical axis of rotation. In this case the scapula is fixed and the humerus is free to rotate. The line of force of the pectoralis major is shown with its internal moment arm. Note the roll-and-slide arthrokinematics of the convex-on-concave motion. For clarity, the anterior deltoid is not shown.

70. SHOULDER INSTABILITY Posttraumatic Instability Atraumatic Instability
Acquired Shoulder Instability
Dr. Michael P. Gillespie

71. POSTTRAUMATIC INSTABILITY
Posttraumatic instability is attributed to a specific event involving a traumatic dislocation of the glenohumeral joint.
The vast majority of traumatic dislocations occur in the anterior direction, typically related to a fall or forceful collision.
The pathomechanics of an anterior dislocation often involve the motion or position of extreme external rotation in an abducted position.
The force then drives the humeral head off the anterior aspect of the glenoid fossa.
This dislocation often injures the rotator cuff muscles, middle and inferior GH ligaments, and anterior-inferior rim of the glenoid labrum (Bankart lesions).
Posttraumatic dislocations frequently lead to future recurrences.
Posttraumatic instability does NOT respond well to conservative care and often requires surgery.
Dr. Michael P. Gillespie

72. ATRAUMATIC INSTABILITY
These individuals tend to display generalized and excessive ligamentous laxity throughout the body, often described as being congenital.
This type of instability is usually not associated with a traumatic event.
The instability can be unidirectional or multidirectional, and bilateral.
Atraumatic instability tends to respond favorably to conservative therapy involving strengthening and coordination exercises.
Dr. Michael P. Gillespie

73. ACQUIRED SHOULDER INSTABILITY
The pathogenics of acquired shoulder instability are related to overstretching and subsequent microtrauma of the capsular ligaments within the GH joint.
This condition is associated with repetitive, high- velocity shoulder motions that involve extreme external rotation and abduction.
These motions are common in throwing sports, swimming, tennis, and volleyball.
The anterior bands of the inferior GH ligament and to a lesser extent the middle GH ligament are vulnerable to plastic deformation.
This tissue deformation leads to increased laxity.
This can contribute to other conditions such as rotator cuff syndrome and internal impingement syndrome.
Dr. Michael P. Gillespie

74. SUPRASPINATUS VULNERABILITY
The supraspinatus is one of the most used muscles of the entire shoulder complex.
It assists the deltoid during abduction.
It provides dynamic and static stability to the GH joint.
It is subjected to large internal forces even during routine activities.
The muscle exhibits a 1:20 mechanical advantage over a load in the hand, implying that the muscle must exert a force 20 times greater than the weight of the load.
This can lead to tears of the muscle as it inserts into the capsule and greater tubercle of the humerus.
Dr. Michael P. Gillespie

75. SHOULDER IMPINGEMENT SYNDROME
Subacromial shoulder impingement syndrome is among the most common painful disorders of the shoulder.
It is caused by repeated an unnatural compression of the tissues within the subacromial space.
The tissues affected are the supraspinatus tendon, the tendon of the long head of the biceps brachii, the superior capsule, and the subacromial bursa.
These tissues become compressed between the humeral head and the coracoacromial arch.
This impingement can be a very important factor in rotator cuff syndrome.
Dr. Michael P. Gillespie

76. DIRECT OR INDIRECT CAUSES OF SHOULDER IMPINGEMENT SYNDROME
Abnormal kinematics at the glenohumeral and scapulothoracic joints.
“Slouched” posture that affects the alignment of the scapulothoracic joint.
Fatigue, weakness, poor control, or tightness of the muscles that govern motions at the GH or scapulothoracic joints.
Inflammation and swelling of tissues within and around the subacromial space.
Excessive wear and subsequent degenration of the tendons of the rotator cuff muscles.
Instability of the GH joint.
Adhesions within the inferior GH joint capsule.
Excessive tightness in the posterior capsule of the GH joint (and associated anterior migration of the humeral head towards the lower margin of the coracoacromial arch).
Abnormal shape of the acromion or coracoacromial arch.
Dr. Michael P. Gillespie