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Glenohumeral Joint Anatomy, Stabilizer, and Biomechanics

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Topic updated on 12/18/14 5:25pm
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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Qbank (6 Questions)

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

1. Anteriorly translated with the arm in 90 degrees of abduction and externally rotated
2. Inferiorly translated with the arm in 5 degrees of adduction
3. Anteriorly translated with the arm in 90 degrees of abduction and internally rotated
4. Inferiorly translated with the arm in 45 degrees of abduction and internal rotation
5. Inferiorly translated with the arm in 90 degrees of abduction and neutral rotation

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic
FIGURES: A          

1. Artery labeled 1
2. Artery labeled 2
3. Artery labeled 3
4. Artery labeled 4
5. Artery labeled 5

PREFERRED RESPONSE ▶
TAG
(OBQ12.154) What is the primary function of the structure labeled with an asterisk in Figure A? Topic Review Topic
FIGURES: A          

1. Prevents inferior translation of the humerus with the arm by the side
2. Provides internal rotation of the humerus
3. Prevents anterior translation of the humerus with the arm in 45 degrees of abduction
4. Prevents anterior translation of the humerus with the arm in 90 degrees of abduction
5. Provides supination of the forearm and elbow flexion

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

1. Superior glenohumeral ligament
2. Middle glenohumeral ligament
3. Teres major muscle
4. Deltoid muscle
5. Rotator cuff muscles

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

1. The coracohumeral ligament only
2. The coracohumeral and superior glenohumeral ligaments
3. The coracohumeral, superior and middle glenohumeral ligaments
4. The superior and middle glenohumeral ligaments
5. The superior glenohumeral ligament only

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic
FIGURES: A          

1. Inferior glenohumeral ligament (IGHL)
2. Middle glenohumeral ligament (MGHL)
3. Superior glenohumeral ligament (SGHL)
4. Coracohumeral ligament (CHL)
5. Coracoacromial ligament (CA)

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic

1. Shape of the bony articulation
2. Negative intra-articular pressure
3. Superior gleno-humeral ligament complex
4. Middle gleno-humeral ligament complex
5. Inferior gleno-humeral ligament complex

PREFERRED RESPONSE ▶



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