Shoulder Flashcards
What are the four mechanically interrelated articulations of the shoulder complex?
- Sternoclavicular (SC) Joint
- Acromioclavicular (AC) Joint
- Scapulothoracic (ST) ‘Joint’
- Glenohumeral (GH) Joint
What is the primary design purpose of the shoulder complex?
Mobility
What type of joint is the sternoclavicular (SC) joint?
Synovial, saddle joint
What is the only structural attachment between the axial skeleton and the shoulder/upper extremity?
Sternoclavicular Joint
How many degrees of freedom does the SC joint have for rotational movements?
3
What are the three rotational degrees of freedom of the SC joint?
- Elevation/depression of clavicle
- Protraction/retraction of clavicle
- Anterior/posterior rotation of clavicle
What is the range of motion (ROM) for clavicular elevation at the SC joint?
Up to 48°
What role does the SC disc play in the SC joint?
Acts as a pivot point for medial end of clavicle during movements
What are the main components of the sternoclavicular capsule?
- Anterior & posterior sternoclavicular ligaments
- Bilaminar costoclavicular ligament
- Interclavicular ligament
What type of joint is the acromioclavicular (AC) joint?
Incongruent plane, synovial joint
What are the main functions of the acromioclavicular joint?
- Allows scapula to move in 3 dimensions during arm movement
- Increases upper extremity motion
- Positions glenoid beneath humeral head
- Helps maximize scapula contact with thorax
- Assists in force transmission from upper extremity to clavicle
True or False: The acromioclavicular joint is inherently stable.
False
What are the two portions of the coracoclavicular ligament?
- Conoid ligament
- Trapezoid ligament
What kinematic motions occur at the acromioclavicular joint?
- Internal/external rotation
- Anterior/posterior tilting
- Upward/downward rotation
What is the principal motion of the scapula during active elevation of the arm?
Upward rotation
What muscles are primarily responsible for scapular protraction?
- Serratus anterior
- Pectoralis major
- Pectoralis minor
What type of joint is the glenohumeral joint?
Ball & socket, synovial joint
What is the orientation of the glenoid fossa typically?
Slightly tilted upward
What is the consequence of reduced stability in the glenohumeral joint?
Increased susceptibility to instability, injury, and degenerative changes
What occurs during anterior tilting of the scapula?
Acromion moves forward & inferior angle moves posteriorly
What happens during posterior tilting of the scapula?
Acromion moves backward & inferior angle moves anteriorly
Fill in the blank: The scapulothoracic joint is not a true _______.
[anatomic joint]
What is retroversion in relation to the glenoid fossa?
Retroversion refers to the glenoid fossa facing slightly posterior.
Most commonly, the glenoid is in slight retroversion (6° - 7°).
What are the articular surfaces of the glenohumeral joint?
The articular surfaces include the humeral head, which forms 1/3 to 1/2 of a sphere and has a larger surface area than the glenoid.
When arms hang dependently at the side, there is little contact between these surfaces.
What is the normal angle of inclination for the glenohumeral joint?
The normal angle of inclination is between 130° - 150°.
Define the angle of torsion in the glenohumeral joint.
The angle of torsion is formed by an axis through the humeral head and neck in relation to an axis through the humeral condyles.
What is the function of the glenoid labrum?
The glenoid labrum enhances the articular surface, increases depth/concavity of the fossa, resists humeral head translations, protects bony edges of the fossa, minimizes GH friction, and dissipates joint contact forces.
What are the components of the glenohumeral joint capsule?
The glenohumeral joint capsule is large and loose, taut superiorly and loose inferiorly when the arm is at rest by the side.
It maximally tightens when the arm is fully abducted and externally rotated.
List the ligaments that reinforce the glenohumeral joint.
- Superior GH ligament
- Middle GH ligament
- Inferior GH ligament
- Coracohumeral ligament
What is the rotator interval capsule?
The rotator interval capsule is comprised of the superior GH capsule, superior GH ligament, and coracohumeral ligament, bridging the gap between the supraspinatus and subscapularis tendons.
True or False: The middle GH ligament limits anterior humeral translation with the arm at side and up to 60° of abduction.
True.
What is the function of the inferior glenohumeral ligament complex (IGHLC)?
The IGHLC stabilizes the joint with abduction greater than 45° or with combined abduction and rotation.
What does the coracohumeral ligament do?
The coracohumeral ligament limits inferior translation of the humeral head in a dependent arm position and resists lateral rotation with the arm adducted.
What forms the coracoacromial arch?
The coracoacromial arch is formed by the coracoid process, undersurface of the acromion, coracoacromial ligament, and inferior surface of the AC joint.
What is the primary content of the subacromial space?
- Subacromial bursa
- Rotator cuff tendons
- Long head of biceps tendon
What is the normal range of motion for glenohumeral flexion and extension?
- Flexion: ~120°
- Extension: ~50°
Fill in the blank: ER of humerus is needed for full _______.
[abduction]
What happens during normal arthrokinematics with shoulder abduction?
The humeral head undergoes a superior roll and an inferior slide.
What assists in holding the humeral head in place at rest?
- Joint capsule creates negative intra-articular pressure
- Slight upward tilt of the glenoid fossa
- Downward pull of gravity opposed by passive tension in rotator interval capsule
What contributes to dynamic stabilization of the glenohumeral joint?
- Force of the prime mover or movers
- Force of gravity
- Force of the muscular stabilizers
- Articular surface geometry
- Passive capsuloligamentous forces
- Force of friction within joint
- Joint reaction force
What role do rotator cuff muscles play in dynamic stabilization?
Rotator cuff muscles contribute to dynamic stability by compressing the humeral head into the glenoid and producing rotation with minimal translation.
What is the role of the long head of the biceps tendon in the glenohumeral joint?
The long head of the biceps tendon appears to center the humeral head in the fossa and reduce vertical and anterior translations.
List the muscles involved in glenohumeral flexion.
- Deltoid (anterior)
- Pectoralis major (clavicular head)
- Biceps brachii
- Coracobrachialis
List the muscles involved in glenohumeral abduction.
- Supraspinatus
- Deltoid (middle)
- Pectoralis major
- Latissimus dorsi
- Teres major
- Coracobrachialis
What is the scapulohumeral rhythm during shoulder elevation?
The scapulohumeral rhythm has a ratio of 2° of GH motion to 1° of ST motion.
What muscles are involved in upward rotation of the scapula?
- Upper trapezius
- Serratus anterior
- Lower trapezius
What muscles are involved in downward rotation of the scapula?
- Levator scapulae
- Rhomboids
- Pectoralis minor
