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Planes of Motion
  • Reference
    • scapular plane is 30 degrees anterior to coronal plane.
  • Abduction
    • abduction requires external rotation to clear the greater tuberosity from impinging on the acromion.
      • therefore if someone has an internal rotation contracture they can not abduct > 120
    • 180° of abduction comes from motion in two joints (2:1 ratio)
      • 120° from the glenohumeral joint
      • 60° from the scapulothoracic joint
Glenohumeral Stability
  • Static restraints
    • glenohumeral ligaments (below)
    • glenoid labrum (below)
    • articular congruity and version
    • negative intraarticular pressure
      • if release head will sublux inferiorly
  • Dynamic restraints
    • rotator cuff muscles
      • the primary biomechanical role of the rotator cuff is stabilizing the glenohumeral joint by compressing the humeral head against the glenoid
    • biceps
    • periscapular muscles
Glenohumeral Ligaments (static)

Ligamentous Restraints in different Arm Positions
Arm Position
Anterior Res.
Inferior Res.
Posterior Res.
0° (side) and adduction
x
SGHL/CHL
xxx
45° (ER) and 45° abducted
MGHL
x
MGHL
Adduction   SGHL/CHL  
90° (ER)
Anterior band IGHL
Anterior band IGHL
Posterior band IGHL
90° (forward flexed, abduction, and IR)
Anterior band IGHL
 
Posterior band IGHL
SGHL/CHL
 
  • SGHL  
    • restraint to inferior translation at 0° degrees of abduction (neutral rotation)
  • MGHL  
    • resist anterior and posterior translation in the midrange of abduction (~45°) in ER  
  • IGHL  
    • posterior band IGHL
      • most important restraint to posterior subluxation at 90° flexion and IR
      • tightness leads to internal impingement and increased shear forces on superior labrum (linked to SLAP lesions)
    • anterior band IGHL
      • stability
        • primary restraint to anterior/inferior translation 90° abduction and maximum ER (late cocking phase of throwing)
      • anatomy
        • anchors into anterior labrum
        • forms weak link that predisposes to Bankart lesions
    • superior band IGHL
      • most important static stabilizer about the joint
      • 100% increased strain on superior band of IGHL in presence of a SLAP lesion
  • Coracohumeral ligament (CHL)
    • limits posterior translation with shoulder in flexion,adduction, and internal rotation
    • limits inferior translation and external rotation at adducted position
Glenoid Labrum (static)
  • Function
    • helps create cavity-compression and creates 50% of the glenoid socket depth
  • Composition
    • composed of fibrocartilagenous tissue
  • Blood supply
    • suprascapular artery
    • anterior humeral circumflex scapular
    • posterior humeral circumflex arteries
    • labrum receives blood from capsule and periosteal vessels and not from underlying bone
    • anterior-superior labrum has poorest blood supply
  • Stability
    • anterior labrum
      • anchors IGHL (weak link that leads to Bankart lesion)
    • superior labrum
      • anchors biceps tendon (weak link that leads to SLAP lesion)
  • Anatomic variants
    • normal variant
      • the labrum attached to the glenoid rim and a flat/broad middle glenohumeral ligament is the most common “normal” variation. A cord-like middle glenohumeral ligament is often
      • present in 86% of population
    • sublabral foramen
      • seen in ~12% if population
    • Buford complex
      • seen in ~1.5% of population
      • cordlike middle glenohumeral ligament with attachment to base of biceps anchor and complete absence of the anterosuperior labrum
      • attaching a Buford complex will lead to painful and restricted external rotation and elevation.
    • meniscoid appearance (1%)
Soft Tissue Stabilizers
  • Posterior capsule (static)
    • thin (< 1mm) with no ligaments
  • Rotator Interval
    • contracture of the rotator interval is seen with adhesive capsulitis (frozen shoulder)
    • laxity of the rotator interval results in a visible sulcus sign with inferior laxity with the shoulder in adduction
    • includes the capsule, SGHL, coracohumeral ligament and long head biceps tendon that bridge the gap between the supraspinatus and the subscapularis.
    • boundaries
      • medially by lateral coracoid base
      • superiorly by anterior edge of supraspinatus
      • inferiorly by superior border of subscapularis
      • lateral apex formed by transverse humeral ligament
  • Rotator cuff (dynamic)
    • subscapularis is an important stabilizer to posterior subluxation in external rotation
  • Biceps Long Head (dynamic) 
    • long head of biceps acts as humeral head depressor.
    • variable origin from superior labrum
    • forms weak links that predisposes to SLAP tear
Osteology
  • Humeral head
    • greater and lesser tuberosities are attachment sites for the rotator cuff
    • spheroidal in shape in 90% of individuals
    • average diameter is 43 mm
    • retroverted 30° from transepicondylar axis of the distal humerus
    • articular surface inclined upward 130° from the shaft
  • Glenoid
    • pear-shaped surface with average upward tilt of 5°
    • average version is 5° of retroversion in relation to the axis of the scapular body and varies from 7° of retroversion to 10° of anteversion
  • Coracoid
    • serves as an anatomic landmark or "lighthouse" for the deltopectoral approach
    • coracobrachialis, pectoralis minor, and short head of the biceps attach to the coracoid
  • Acromion
    • 3 ossification centers
      • meta (base), meso (mid), and pre-acromion (tip)
    • acromiohumeral interval is 7-8mm
      • AHI may be normal on Xray but decreased on MRI when pt is supine and weight of arm is removed. This usually signifies multiple tendon tear.
    • acromial morphology
      • I=flat
      • II=curved
      • III=hooked
Blood Supply
  • Humeral head
    • ascending branch of anterior humeral circumflex artery and arcuate artery
      • provides blood supply to humeral head
      • vessel runs parallel to lateral aspect of tendon of long head of biceps in the bicipital groove
        • beware not to injure when plating proximal humerus fractures
      • arcuate artery is the interosseous continuation of ascending branch of anterior humeral circumflex artery and penetrates the bone of the humeral head
    • posterior humeral circumflex artery
      • most current literature supports this as providing the main blood supply to humeral head  
Free Body Analysis of Deltoid
  • Free body diagram if the arm was at 90 degs of abduction (not pictured)
    • assuming A = 3cm and B = 30 cm
    • sum of moment M = 0
    • (A x D) - (B x 0.5W) = 0
      • 3D = 0.5W (30)
      • D = 5W
  • Arthrodesis
    • optimal position
      • 15-20° of abduction
      • 20-25° of forward flexion
      • 40-50° of internal rotation
 

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Questions (7)

(OBQ12.62) A 67-year-old female who sustained a proximal humerus fracture as a result of a fall goes on to develop avascular necrosis (AVN). An injury was most likely sustained to which of the following arteries labeled 1-5 in Figure A? Review Topic

QID:4422
FIGURES:
1

Artery labeled 1

0%

(13/3156)

2

Artery labeled 2

1%

(26/3156)

3

Artery labeled 3

17%

(548/3156)

4

Artery labeled 4

81%

(2549/3156)

5

Artery labeled 5

0%

(7/3156)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

The artery labeled 4 on the arteriogram is the posterior humeral circumflex artery, which is the primary blood supply to the humeral head, and most likely to lead to AVN when injured.

While previous literature suggested that the anterior humeral circumflex artery provided the main blood supply to the humeral head, more current literature supports the posterior circumflex humeral artery as the predominant blood supply. Despite the anterior humeral circumflex artery being disrupted in approximately 80% of proximal humeral fractures, the occurence of resultant osteonecrosis is still infrequent. This inconsistency suggests a greater role for the posterior humeral circumflex artery.

Hettrich et al. performed a cadaveric study assessing the vascularity of the proximal part of the humerus. They injected gadolinium into the axillary artery proximally, and then either the anterior humeral circumflex artery or the posterior humeral circumflex artery was ligated. MRI was then performed and the specimens were dissected to determine the dominant blood supply. They found that the posterior humeral circumflex artery provided 64% of the blood supply to the humeral head, whereas the anterior humeral circumflex artery supplied 36%. The posterior humeral circumflex artery also provided significantly more of the blood supply in three of the four quadrants of the humeral head.

Hertel et al. assessed predictors of humeral head ischemia after fractures of the proximal humerus. Their results concluded that the most predictive factors for humeral head ischemia included the >8mm length of the dorsomedial metaphyseal extension, disrupted integrity of the medial hinge, and the complicated and communited fracture types.

Crosby et al. used tetracycline labeling as a measure to study humeral head viability after 3- or 4-part proximal humerus fractures taken at the time of hemiarthroplasty. Their findings showed that the vascular supply was preserved in all of the resected specimens including displaced three- and four-part proximal humerus fractures especially in younger patients. They recommended that with intact vascularity to the humeral head, head-preserving techniques utilizing stable, site-specific fixation and minimal dissection should be considered in the treatment of displaced three- and four-part proximal humerus fractures.

Illustration A shows a labeled arteriogram of the blood vessels near the shoulder.

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(OBQ12.154) What is the primary function of the structure labeled with an asterisk in Figure A? Review Topic

QID:4514
FIGURES:
1

Prevents inferior translation of the humerus with the arm by the side

8%

(263/3225)

2

Provides internal rotation of the humerus

13%

(418/3225)

3

Prevents anterior translation of the humerus with the arm in 45 degrees of abduction

61%

(1977/3225)

4

Prevents anterior translation of the humerus with the arm in 90 degrees of abduction

16%

(501/3225)

5

Provides supination of the forearm and elbow flexion

1%

(35/3225)

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PREFERRED RESPONSE 3

The labeled structure is the middle glenohumeral ligament (MGHL) of the shoulder. The primary function of the MGHL is to prevent anterior translation of the humeral head with the arm in 45-60 degrees of abduction.

This structure originates from the glenoid labrum and inserts medial to the lesser tuberosity running obliquely across the subscapularis. The size of the structure may be variable and there are recognized normal anatomic variants (including a cord like MGHL in the Buford complex). It is important to be able to recognize the MGHL and differentiate this from the subscapularis, IGHL, SGHL, and other intraarticular structures in the shoulder to be able to perform effective and precise arthroscopic procedures.

Burkhart et al. describe the function of the glenohumeral ligaments in anterior shoulder instability, noting that the MGHL provides a restraint to anterior translation with the arm in 45-60 degrees of abduction.

Wang et al. discuss microdamage to the inferior glenohumeral ligament from a basic science perspective, indicating that over time it may stretch and compromise it's function in restraining humeral translation.

Figure A is an arthroscopic image of the intraarticular structures of the shoulder with an asterisk on the MGHL. Illustration B shows the associated anatomic structures.

Incorrect Answers (these are labeled on Illustration A, with the exception of the subscapularis which is difficult to visualize):
Answer 1: Describes the superior glenohumeral ligament (1: Illustration A)
Answer 2: Describes the subscapularis (2: Illustration A)
Answer 4: Describes the inferior glenohumeral ligament (4: Illustration A)
Answer 5: Describes the biceps tendon (5: Illustration A)

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(OBQ09.64) What structure provides dynamic glenohumeral stability by compressing the humeral head against the glenoid? Review Topic

QID:2877
1

Superior glenohumeral ligament

1%

(5/648)

2

Middle glenohumeral ligament

2%

(12/648)

3

Teres major muscle

0%

(1/648)

4

Deltoid muscle

4%

(26/648)

5

Rotator cuff muscles

93%

(603/648)

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

The rotator cuff is the main DYNAMIC stabilizer of the glenohumeral joint. It functions most at midrange motion, not at the extremes of range of motion. The superior glenohumeral ligament is a STATIC stabilizer and resists inferior translation at 0° degrees of abduction. The middle glenohumeral ligament is a STATIC stabilizer and resists anterior translation in the midrange of abduction (~45°) in ER. The teres major adducts and medially rotates arm and is not a significant stabilizer of the glenohumeral joint. The deltoid muscle primarily abducts the arm and is not the major stabilizer of the glenohumeral joint.

Hirashima et al. used EMG to characterize the sequential activation of musculature during overarm throwing and postulate that the sequence is very effective for the generation of high force and energy in the trunk.


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Question COMMENTS (3)

(OBQ08.261) Besides the biceps tendon, which of the following structures also pass through the rotator interval? Review Topic

QID:647
1

The coracohumeral ligament only

8%

(136/1808)

2

The coracohumeral and superior glenohumeral ligaments

66%

(1195/1808)

3

The coracohumeral, superior and middle glenohumeral ligaments

13%

(242/1808)

4

The superior and middle glenohumeral ligaments

7%

(125/1808)

5

The superior glenohumeral ligament only

6%

(102/1808)

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PREFERRED RESPONSE 2

The rotator cuff is perforated anterosuperiorly by the coracoid process, which separates the anterior border of the supraspinatus tendon from the superior border of the subscapularis tendon, creating the triangular rotator interval, which is bridged by capsule. The base of the interval is the coracoid process, from which capsular tissue (the coracohumeral ligament) originates. The transverse humeral ligament at the biceps intertubercular sulcus forms the apex of the rotator interval. The coracohumeral and superior glenohumeral ligaments are considered to be structural contents of the rotator interval capsule, but each have separate origins and insertions. These ligaments are considered to be the most constant structures of the fibrous joint capsule.

Arai et al performed cadaver dissections to describe the anatomy as it relates to reconstructing the biceps sling as it exits the interval in cases of biceps subluxation. They note that an intact superior border of subscapularis is needed as well as tension in the SGHL.

Yang et al reported a descriptive anatomy study on the CHL. All were located in the rotator interval, originated from the lateral aspect of the base of the coracoid process, and had histology more consistent with capsule than ligament.

Illustrations A & B show a schematic drawing and a corresponding MRI image of the shoulder that depicts the rotator interval. Boundaries of the rotator interval include the coracoid process (COR) at its base, superiorly by anterior margin of supraspinatus tendon (SST) and inferiorly by superior margin of subscapularis tendon (SSC). Contents of rotator interval include long head of biceps tendon (BT), coracohumeral ligament (CHL), superior glenohumeral ligament (SGHL), and rotator interval capsule. Rotator interval capsule (RIC) is the anterosuperior aspect of glenohumeral joint capsule, which merges with CHL and SGHL insertions medial and lateral to bicipital groove.

Illustration C demonstrates a cadaveric image with the subscapularis tendon (black star), supraspinatus tendon (white star), and rotator interval capsule (asterisk).

Illustration D is an image of a right shoulder in the beachchair position viewed from a posterior portal showing a rotator interval closure for a patient with multidirectional instability of the shoulder.

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(SBQ07.47) The superior glenohumeral ligament is under the greatest stress when the humeral head and arm are in which of the following positions? Review Topic

QID:1432
1

Anteriorly translated with the arm in 90 degrees of abduction and externally rotated

11%

(53/474)

2

Inferiorly translated with the arm in 5 degrees of adduction

72%

(340/474)

3

Anteriorly translated with the arm in 90 degrees of abduction and internally rotated

4%

(21/474)

4

Inferiorly translated with the arm in 45 degrees of abduction and internal rotation

7%

(34/474)

5

Inferiorly translated with the arm in 90 degrees of abduction and neutral rotation

5%

(23/474)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

The role of each glenohumeral ligament has been clearly defined by previous cadaveric studies that have sectioned different ligaments during different periods of stress on the glenohumeral joint. These studies have demonstrated that the superior glenohumeral ligament provides the most restraint to the shoulder joint when the arm is at zero degrees of abduction or in adduction and pulled inferiorly.

Warner et al. tested 11 cadavers with varying amounts of abduction and rotation to see what ligaments provided specific, directional stability to the shoulder joint. They found that the anterior and posterior bands of the inferior glenohumeral ligament provided the most restraint when the arm was abducted. In addition, they found the superior glenohumeral ligament provided the most restraint when the arm was at zero degrees of abduction and pulled inferiorly.

Illustration A shows an anatomic representation of the glenohumeral ligaments.

Incorrect answers:
1: The anterior inferior glenohumeral ligament is stressed when the arm is in this position
3: An arm positioned as such does not classically stress any of the glenohumeral ligaments
4 and 5: The arm is more adducted in answer 2

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Question COMMENTS (1)

(OBQ04.77) Which of the following is a primary restraint of anterior and posterior humeral translation at the position of a patient's right shoulder as shown in Figure A? Review Topic

QID:1182
FIGURES:
1

Inferior glenohumeral ligament (IGHL)

15%

(92/599)

2

Middle glenohumeral ligament (MGHL)

77%

(461/599)

3

Superior glenohumeral ligament (SGHL)

6%

(34/599)

4

Coracohumeral ligament (CHL)

2%

(9/599)

5

Coracoacromial ligament (CA)

0%

(1/599)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

Figure A shows a shoulder in 45 degrees of abduction and 45 degrees of external rotation. The MGHL restrains anterior and posterior translation in the midrange of abduction. The CHL limits inferior translation and external rotation when then arm is adducted and limits posterior translation when the arm is flexed, adducted, and internal rotation. The SGHL also restrains inferior translation and external rotation of the adducted shoulder. The IGHL has an anterior band that is the primary restraint to anterior translation at 90 degrees of shoulder abduction. It also has a posterior band to limit posterior translation. The CA ligament prevents superior head migration in rotator cuff deficient shoulders.

The study by Kuhn et al was a cadaveric study of 20 shoulder specimens mounted in a testing apparatus to simulate the thrower's late-cocking position. They found that cutting the entire inferior glenohumeral ligament resulted in the greatest increase in external rotation (approximately 10 degrees).



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(OBQ04.89) Which of the following is considered the primary static restraint to anterior gleno-humeral translation with the arm in 90 degrees of abduction? Review Topic

QID:1194
1

Shape of the bony articulation

0%

(1/353)

2

Negative intra-articular pressure

1%

(2/353)

3

Superior gleno-humeral ligament complex

10%

(35/353)

4

Middle gleno-humeral ligament complex

26%

(92/353)

5

Inferior gleno-humeral ligament complex

63%

(222/353)

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

The geometry of the bony articulation is inherently unstable. The rotator cuff is a dynamic stabilizer and the capsulolabral tissues are considered static stabilizers. With the arm at 90 degrees abduction, the anterior band of the inferior gleno-humeral ligament complex is the primary static stabilizer to anterior translation. The middle (MGHL) resists anterior translation at 45 degrees of abduction. The superior (SGHL) resists inferior translation with the arm at one's side.

O'Brien et al. describe the functional anatomy of the inferior gleno-humeral complex based on a series of cadaveric dissections. They note that its orientation and design support the functional concept of this single structure as an important anterior and posterior stabilizer of the shoulder joint. The Burra paper is a review of acute upper extremity instability in athletes.


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