Shoulder Anatomy Flashcards
Where is the scapular plane situated relative to the coronal plane?
Scapular plane is 30 degrees anterior to coronal plane.
What does Abduction require?
Where does abduction comes from?
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
What are the Static restraints of the shoulder?
- Glenohumeral ligaments
- Glenoid labrum
- Articular congruity and version
- Negative intra-articular pressure: if release head will sublux inferiorly
Function of GHLigaments
SGHL :
restraint to inferior translation at 0° degrees of abduction (neutral rotation)
prevents antero-inferior translation of long head of biceps (biceps pulley)
MGHL
resist anterior and posterior translation in the mid-range of abduction (~45°) in ER
IGHL
1. 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)
2. anterior band IGHL stability
primary restraint to anterior/inferior translation 90° abduction and maximum ER (late cocking phase of throwing)
anchors into anterior labrum
forms weak link that predisposes to Bankart lesions
Superior band of IGHL:
most important static stabilizer about the joint
100% increased strain on superior band of IGHL in presence of a SLAP lesion
What portion of the labrum has the poorest blood supply?
anterior-superior labrum has poorest blood supply
Normal Variants of labrum
normal variant
- A cord-like middle glenohumeral ligament is often; 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%)
What is the Rotator Interval (static) composed of and what are its boundaries?
capsule, SGHL, coraco-humeral ligament and long head biceps tendon that bridge the gap between the supra-spinatus and the sub-scapularis.
boundaries
medially by lateral coracoid base
superiorly by anterior edge of supra-spinatus
inferiorly by superior border of sub-scapularis
lateral apex formed by transverse humeral ligament
Anatomy of humeral head and glenoid
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
Acromion
Embryology
Acromio-humeral interval
Acromial morphology
3 ossification centers:
meta (base), meso (mid), and pre-acromion (tip)
Acromio-humeral 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
What is the optimal Arthrodesis position?
◦ optimal position
15-20° of abduction
20-25° of forward flexion
40-50° of internal rotation
Motion of the AC joint
majority of motion is from the bones, not through the joint
clavicle rotates 40-50° posteriorly with shoulder elevation
8° of rotation through AC joint
remainder from scapular rotation and sternoclavicular motion
joint itself is limited to gliding motions only
primary restraint for anterior-posterior stability of sterno-clavicular joint?
Posterior sternoclavicular capsular ligament
What is the resting position of the scapulothoracic joint?
Testing position angulation (although these are variable even in healthy adults)
anteriorly 10-20°
internally rotated 30°-45° from the coronal plane
upward tilt of 3°
What are the 17 different muscles attach to or originate from the scapula
trapezius
serratus anterior
deltoid
latisimus dorsi
levator scapulae
rhomboid major
rhomboid minor
omohyoid - inferior belly
pectoralis minor
teres major
teres minor
triceps brachii
biceps brachii
coracobrachialis
infraspinatus
subscapularis
supraspinatus
Os acromiale
Location
Incidence
An unfused secondary ossification center
Most common location is the junction of meso- and meta-acromion
incidence 8%
bilateral in 60%
more common in males
more common in African American
