Shoulder Flashcards
What structure surrounds the AC joint to provide stability?
A joint capsule.
What is the function of the conoid ligament?
Resists elevation and protraction of the clavicle.
Where does the conoid ligament run?
Vertically between the coracoid process and the clavicle.
What is the function of the trapezoid ligament?
Provides AC joint compression.
Where does the trapezoid ligament run?
In a superior and lateral direction between the coracoid process and the clavicle.
What happens to the clavicle during elevation?
Both costoclavicular ligaments develop tension, causing posterior rotation of the clavicle along its long axis.
What forces do the costoclavicular ligaments resist?
Upward rotation forces of the scapula.
What is the function of the acromioclavicular ligament?
Covers the joint capsule and reinforces its superior aspect.
(i.e. strengthens and supports the upper part of the joint capsule.)
Where does the acromioclavicular ligament run?
Horizontally from the acromion to the clavicle.
What surrounds the entire SC joint?
A joint capsule.
Why is the SC joint capsule considered weak?
It relies on ligaments for additional support.
Which ligaments provide anterior and posterior support to the SC joint?
Anterior and posterior sternoclavicular ligaments.
What is the function of the interclavicular ligament?
Provides restraint to inferior forces on the medial end of the clavicle.
Where does the interclavicular ligament span?
Between both medial ends of the clavicles.
What ligaments make up the costoclavicular ligament complex?
An anterior and posterior bundle.
Where does the costoclavicular ligament complex attach?
From the superior surface of the first rib to the undersurface of the clavicle.
What is the function of the costoclavicular ligament complex?
Limits excessive superior, anterior, or posterior movement of the medial end of the clavicle.
What type of joint is the SC joint?
A saddle-shaped joint.
Why is the SC joint considered inherently unstable?
Its bony structure provides minimal stability.
How many degrees of rotation and translation does the SC joint allow?
Three degrees.
What structure within the SC joint enhances stability?
An articular disk.
What is the function of the articular disk in the SC joint?
Provides stability and separates the joint into two compartments.
Despite its instability, why is the SC joint rarely dislocated?
It rarely dislocates due to the support of strong ligaments and surrounding structures.
Which ligament is considered the most important for SC joint stability?
The posterior sternoclavicular ligament.
What happens when the posterior sternoclavicular ligament is sectioned?
Significant increases in anterior and posterior translation occur.
How does the costoclavicular ligament act as a fulcrum?
by causing the medial end of the clavicle to move in the mirror opposite direction of the lateral end of the clavicle during movement.
What is the shape of the medial end of the clavicle in the anterior-posterior direction?
Concave.
What is the shape of the medial end of the clavicle in the superior-inferior direction?
Convex.
What type of bone is the scapula?
A large, flat, thin, triangular-shaped bone.
Where does the medial border of the scapula rest in relation to the thoracic vertebral column?
Approximately 5 cm (3 fingers width) from the thoracic vertebral column.
Why is the scapulothoracic joint considered a “pseudo joint”?
It lacks the typical characteristics of synovial joints.
What structures form the scapulothoracic joint?
The anterior portion of the scapula and the posterior thorax and rib cage.
At what vertebral levels does the scapula rest superiorly and inferiorly?
Superiorly at T2, inferiorly at T7.
At what vertebral level does the spine of the scapula rest?
T3.
How is the scapulothoracic joint angled from the coronal plane?
About 30° to 45° to position the glenoid fossa anteriorly in the “scaption” plane.
How is the scapula oriented in terms of rotation and tilt?
It is upwardly rotated about 10° to 20° and tips anteriorly about 10° to 20° from vertical.
What is the function of the acromion?
Serves as a lever arm for the deltoid and articulates with the lateral end of the clavicle at the AC joint.
What is the arthrokinematic motion of the GH joint during flexion?
Posterior glide and anterior roll.
What is the arthrokinematic motion of the GH joint during internal rotation?
Posterior glide and anterior roll.
What is the arthrokinematic motion of the GH joint during horizontal adduction?
Posterior glide and anterior roll.
What is the arthrokinematic motion of the GH joint during extension?
Anterior glide and posterior roll.
What is the arthrokinematic motion of the GH joint during external rotation?
Anterior glide and posterior roll.
What is the arthrokinematic motion of the GH joint during horizontal abduction?
Anterior glide and posterior roll.
What is the arthrokinematic motion of the GH joint during abduction?
Inferior glide and superior roll.
What is the arthrokinematic motion of the GH joint during adduction?
Superior glide and inferior roll.
What is the AC joint arthrokinematic motion during flexion?
Posterior spin
(superior roll, inferior glide)
What is the AC joint arthrokinematic motion during extension?
Anterior spin
(inferior roll, superior glide)
What is the AC joint arthrokinematic motion during adduction?
Superior glide.
What is the AC joint arthrokinematic motion during abduction?
Inferior glide.
What is the AC joint arthrokinematic motion during internal rotation?
Anterior glide.
What is the AC joint arthrokinematic motion during external rotation?
Superior glide.
What is the SC joint arthrokinematic motion during flexion?
Inferior glide.
What is the SC joint arthrokinematic motion during extension?
Superior glide.
What is the SC joint arthrokinematic motion during horizontal abduction and protraction?
Anterior glide and roll.
What is the SC joint arthrokinematic motion during horizontal adduction and retraction?
Posterior glide and roll.
What is the normal ROM and end feel for shoulder flexion?
180° elevation; firm end feel.
What is the normal ROM and end feel for shoulder extension?
45°-60° extension; firm end feel.
What is the normal ROM and end feel for shoulder external rotation?
80°-110° ER (more for throwers); firm end feel.
What is the normal ROM and end feel for shoulder internal rotation?
70°-90° IR; firm end feel.
What is the normal ROM and end feel for shoulder abduction?
180° elevation; firm end feel.
What is the normal ROM and end feel for shoulder adduction?
30°-50° adduction; soft end feel.
What is the normal ROM and end feel for shoulder horizontal abduction?
45°; firm end feel.
What is the normal ROM and end feel for shoulder horizontal adduction?
35°-45°; firm or soft tissue end feel.
What is the open packed position of the GH joint?
55° abduction, 30° horizontal adduction.
What is the open packed position of the AC joint?
Arm resting at side.
What is the open packed position of the SC joint?
Arm resting at side.
What is the closed packed position of the GH joint?
90° abduction, full ER
What is the closed packed position of the AC joint?
90° abduction.
What is the closed packed position of the SC joint?
Full shoulder elevation.
What is the capsular pattern of the GH joint?
ER, abduction (flexion), IR.
What is the capsular pattern of the AC joint?
Pain at end range.
What is the capsular pattern of the SC joint?
Pain at end range.
What is the classic scapulohumeral rhythm ratio?
2° of GH motion for every 1° of scapular motion.
What is the range of reported scapulohumeral rhythm ratios?
Between 1.25:1 to 4:1.
How much GH motion contributes to full 180° of shoulder elevation?
120° of humeral elevation.
How much scapular motion contributes to full 180° of shoulder elevation?
60° of scapular rotation.
Why must the humerus externally rotate during elevation?
To prevent the greater tubercle of the humerus from bumping into the acromion.
How much external rotation of the humerus is needed for clearance?
35°-45°.
During the initial phase of humeral elevation (20-30°), how much scapular motion occurs?
None.
How much ST upward rotation occurs during full shoulder elevation?
60°.
What are the components of the 60° of ST upward rotation?
25° of SC elevation and 35° of AC posterior (upward) rotation.
(Includes 25° of SC posterior rotation and 10° of AC joint external rotation.)
What is the directional force of the deltoid during initial arm elevation?
Upward and outward.
What would happen if the deltoid acted unopposed during humeral elevation?
The greater tuberosity would jam into the undersurface of the acromion, causing superior migration (causing it to move up too much).
Which muscles counteract the superior-directed force of the deltoid?
Infraspinatus, subscapularis, and teres minor.
What is the function of the supraspinatus in the deltoid-rotator cuff force couple?
Provides direct compression, stabilizing the humeral head into the glenoid.
How does the deltoid-rotator cuff force couple work?
The vertical force of the deltoid is offset by the horizontal force of the rotator cuff, acting in opposite directions to create stability.
Which muscles contribute to the trapezius and serratus anterior force couple?
Upper trapezius, lower trapezius, and lower serratus anterior.
What is the primary movement created by the trapezius and serratus anterior force couple?
Upward rotation of the scapula during full elevation.
What are the four key functions of the trapezius and serratus anterior force couple?
- Rotates the scapula to maintain optimal position of the humerus head on the glenoid surface
- Maintains an efficient length-tension relationship for the deltoid (for efficient contraction).
- Prevents impingement of the rotator cuff from subacromial structures.
- Stabilizes the scapula for proper scapulohumeral muscle recruitment.
Which muscles make up the anterior-posterior rotator cuff force couple?
Subscapularis (anterior), infraspinatus, and teres minor (posterior).
What two key functions does the anterior-posterior rotator cuff force couple provide?
- Inferior dynamic stability.
- (i.e. Prevent the humeral head from moving inferiorly out of the glenoid during arm movements) - Concavity-compression mechanism.
- (i.e. the humeral head is pressed into the glenoid cavity by the rotator cuff muscles)
How do the rotator cuff muscles act as a “suspension bridge?”
They provide a stable fulcrum, allowing for concentric rotation of the humeral head on the glenoid.
At what range of motion are the anterior-posterior rotator cuff muscles most active?
Mid ranges of shoulder elevation.
How do these muscles contribute to shoulder stability?
They depress and compress the humeral head into the glenoid.
Why does the anterior-posterior force couple remain intact even with an isolated supraspinatus tear?
Because the subscapularis, infraspinatus, and teres minor still provide balanced anterior-posterior stability.
What are the primary actions of the serratus anterior muscle?
Protracts, upwardly rotates, and stabilizes the scapula against the thorax.
What nerve innervates the serratus anterior?
Long thoracic nerve (C5-C7).
Where does the serratus anterior originate and insert?
Originates from lateral ribs 1-8(9), inserts on the anterior medial margin of the scapula (costal side).
Which muscles work with the serratus anterior for upward scapular rotation?
Upper and lower trapezius.
What is the primary muscle responsible for scapular protraction to achieve full shoulder elevation?
Serratus anterior.
What happens to the serratus anterior in a resting posture of retraction?
It is lengthened.
What clinical sign indicates serratus anterior weakness?
Scapular winging, especially during elevation.
