Updated: 9/9/2022

Glenohumeral Joint Anatomy, Stabilizer, and Biomechanics

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Flashcards
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Questions
18
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Evidence
29
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Videos / Pods
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Images
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https://upload.orthobullets.com/topic/3032/images/meniscoid labrum_moved.jpg
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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 present in shoulder
        • motion occurs at two joints
          • 120° from the glenohumeral joint (2/3)
          • 60° from the scapulothoracic joint (1/3)
  • 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
      • rotator interval
      • biceps long head
      • periscapular muscles
  • Glenohumeral Ligaments (static)
      • Ligamentous Restraints in different Arm Positions
      • Arm position
      • Anterior restraint 
      • Inferior restraint
      • Posterior restraint
      • 0° (side) and adduction
      • SGHL/CHL
      • 45° (ER) and 45° abducted
      • MGHL
      • MGHL
      • 90° (ER)
      • Anterior band IGHL
      • Anterior band IGHL
      • Posterior band IGHL
      • 90° (forward flexed, abduction, and IR)
      • Anterior band IGHL
      • SGHL/CHL
    • SGHL
      • from anteriosuperior labrum to humerus
      • restraint to inferior translation at 0° degrees of abduction (neutral rotation)
      • prevents anteroinferior translation of long head of biceps (biceps pulley)
    • 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)
      • from coracoid to rotator cable
      • 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 present in 86% of population
      • sublabral foramen
        • seen in ~12% if population
      • sublabral foramen + cordlike MGHL
      • Buford complex (absent anterosuperior labrum + cordlike MGHL)
        • 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 (static)
      • 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)
      • the primary biomechanical role of the rotator cuff is stabilizing the glenohumeral joint by compressing the humeral head against the glenoid 
    • 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
      • SGHL and subscapularis thought to play role in stabilizing long head of biceps
  • 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
      • approximate retroversion 20° 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
Flashcards (60)
Cards
1 of 60
Questions (18)

(OBQ18.253) What is the function of the structure indicated by the arrow in Figure A, visualized through the posterior portal in the lateral decubitus position?

QID: 213149
FIGURES:

Resists inferior translation of the humerus at 0 degrees abduction

11%

(256/2315)

Resists anterior and posterior translation of the humerus at 45 degrees abduction

69%

(1592/2315)

Resists posterior translation of the humerus at 90 degrees flexion and internal rotation

8%

(186/2315)

Resists posterior translation of the humerus with shoulder in flexion, adduction, and internal rotation

4%

(100/2315)

Functions to internally rotate the humerus

6%

(150/2315)

N/A A

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

QID: 4514
FIGURES:

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

8%

(500/6301)

Provides internal rotation of the humerus

12%

(781/6301)

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

64%

(4062/6301)

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

13%

(839/6301)

Provides supination of the forearm and elbow flexion

1%

(56/6301)

L 1 A

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(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?

QID: 4422
FIGURES:

Artery labeled 1

0%

(18/5166)

Artery labeled 2

1%

(45/5166)

Artery labeled 3

19%

(957/5166)

Artery labeled 4

80%

(4110/5166)

Artery labeled 5

0%

(7/5166)

L 1 B

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

QID: 2877

Superior glenohumeral ligament

1%

(48/3364)

Middle glenohumeral ligament

2%

(81/3364)

Teres major muscle

1%

(24/3364)

Deltoid muscle

3%

(116/3364)

Rotator cuff muscles

91%

(3073/3364)

L 1 C

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

QID: 647

The coracohumeral ligament only

6%

(227/3958)

The coracohumeral and superior glenohumeral ligaments

69%

(2733/3958)

The coracohumeral, superior and middle glenohumeral ligaments

13%

(513/3958)

The superior and middle glenohumeral ligaments

6%

(234/3958)

The superior glenohumeral ligament only

6%

(221/3958)

L 1 C

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(SAE07SM.95) A 15-year-old wrestler sustains an abduction, hyperextension, and external rotation injury to his right shoulder. The MRI scan findings shown in Figures 27a and 27b are most consistent with

QID: 8757
FIGURES:

an avulsion of the lesser tuberosity.

3%

(20/679)

a midsubstance tear of the capsule.

1%

(9/679)

a tear of the anterior inferior labrum.

19%

(128/679)

a tear of the subscapularis.

11%

(77/679)

a tear of the humeral insertion of the inferior glenohumeral ligament.

65%

(441/679)

L 3 E

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(SBQ07SM.47) The superior glenohumeral ligament is under the greatest stress when the humeral head and arm are in which of the following positions?

QID: 1432

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

12%

(264/2204)

Inferiorly translated with the arm in 5 degrees of adduction

69%

(1531/2204)

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

5%

(102/2204)

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

8%

(174/2204)

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

5%

(104/2204)

L 1 C

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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?

QID: 1194

Shape of the bony articulation

1%

(16/1326)

Negative intra-articular pressure

1%

(10/1326)

Superior gleno-humeral ligament complex

8%

(105/1326)

Middle gleno-humeral ligament complex

22%

(287/1326)

Inferior gleno-humeral ligament complex

68%

(897/1326)

L 1 D

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Evidence (29)
VIDEOS & PODCASTS (16)
EXPERT COMMENTS (42)
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