Week 3 Biomechanics of Glenohumeral (shoulder) joint Flashcards
angle of inclination 傾角
and angle of torsion 扭轉
of head of humerus
angle of inclination: 130-150 degrees (coronal plane)
angle of torsion: 30 degrees posteriorly (transverse plane)
degrees of flexion, extension, abduction and internal/ external rotation of GH movement
flexion: 97-120 degrees
extension: 50 degrees
abduction: large variation of 90-120 degrees
internal/ external rotation:
- in 0 degrees abduction: arc 60 degrees
- in 90 degrees abduction: arc of up to 120 degrees
GH joint stability (static)
– Ligaments (especially superior &
coracohumeral in resting position)
– Capsule
– Glenoid labrum
– Negative intra-articular pressure
– LH biceps tendon
– Orientation of glenoid fossa
GH joint stability (dynamic)
rotator cuff muscles
functions of glenoid labrum
- enhance stability by increasing the depth of the glenoid fossa by 50%
- attachment site for glenohumeral ligaments
close packed position of GH joint
abduction and external rotation
GH joint movement - abduction
humeral head rolls superiorly and slides inferiorly
GH joint movement - flexion/ extension
humeral head tends to spin about relatively fixed point on the glenoid fossa
GH joint movement - internal rotation
humeral head slides posteriorly and rolls anteriorly
GH joint movement - external rotation
humeral head slides anteriorly and rolls posteriorly
functions of the shoulder complex muscles
pivot and stabilise the scapula 樞轉
protect the GH joint
position the humerus at the GH joint
propel the trunk on the humerus
muscles that influence GH joint
trunk –> shoulder girdle
shoulder girdle –> humerus
trunk –> humerus
trunk –> shoulder girdle (scapula)
- trapezius
- serratus anterior
- levator scapulae
- rhomboids
- pectoralis minor
shoulder girdle –> humerus
- GH protectors: supraspinatus, infraspinatus, subscapularis, teres minor
- humeral positioners: deltoid, teres major, coracobrachialis
trunk –> humerus
- pectoralis major
- latissimus dorsi
scapular pivoters
- the position of scapula is to allow muscles to develop force and move the upper limb efficiently
- no muscles produces scapular rotation (force couples)
glenohumeral protectors
rotator cuff muscles - stabilise GH joint
1. supraspinatus - arm abduction
2. infraspinatus - lateral rotates arm
3. teres minor - lateral rotates arm
4. subscapularis - adducts arm
factors that may contribute to subacromial impingement
- scapular position
- humeral position
- anatomical structure of acromion
- muscular imbalance/ control
- pain / inhibition of muscular control
- poor mechanics
what is the humeral positioners
deltoid
- powerful abductor, multipennate muscle
- deltoid activity peaks at 90 degrees abduction
- third class lever, mechanical disadvantage
mechanical disadvantage = imparts speed to end of lever (hand)
why deltoid is mechanical disadvantage through most of range, but it still suited for shoulder abdcution?
- large physiological cross section
- multipennate fibre arrangement
- greater tuberosity acts as an anatomical pulley to improve moment arm
angle of pull (rotary force) of deltoid improves throughout range of shoulder abduction, relies on
三角肌的拉角（旋轉力）在肩部外展的整個範圍內得到改善，依賴…
-
scapular movement and stability:
- upward rotation of scapula maintains the distance between proximal and distal attachments of deltoid; therefore, less active insufficiency of deltoid strong rotator cuff muscles
what is inferior translation
offsets superior pull of deltoid (force couple) during abduction
which three rotator cuff muscles produce an inferior translation
infraspinatus
teres minor
subscapularis
propeller muscles
-
pectoralis major (clavicular and sternal head)
adducts and medially rotates humerus -
latissimus dorsi
OKC - extends, adducts and medially rotates of humerus
CKC - lift the body towards arm
what can latissimus dorsi can do
- weight bearing through hands (crutches, walking stick)
- assist in compensating for Trendlenburg gait
