- Discussion:
- see:
rotator cuff
- abduction of shoulder is a smooth, integrated motion which has been termed
scapulohumeral rhythm by Codman;
- disruption of this smooth motion is important since asymmetrical movement usually indicates a chronic pathological disorder of the shoulder;
- there is a
2:1 ratio of movement in
GHJ & scapulothoracic joints;
-
clavicle also plays part in elevation of the arm, w/ about 40 deg of motion occurring at sternoclavicular joint & 20 deg in
AC joint during full
abduction of the shoulder;
- Role of Rotator Cuff in Shoulder Abduction:
- w/
suprascapular nerve block (which elminates
supraspinatus &
infraspinatus function) there is still full abduction of arm although it is
about 50% weaker;
- remaining teres minor and subscapularis provide glenohumeral compression and humeral depression;
- as arm is abducted to 90 deg direction of pull of deltoid approximates that of the supraspinatus;
- hence pts w/ large tears of
rotator cuff can often actively keep the arm abducted to 90 deg but may not be able to initiate abduction to 90 deg;
