Biomech
7/8/99
Shoulder
- SCJ—don't forget it
- Clavicle—only bone that connects the axial and appendicular skeleton
- The plane of the scapula is 30°
to 50°
Clavicle
- At 90°
of abduction the clavicle has to rotate
Scapula
- 2:1 ratio (15°
of elevation of the arm, 5°
of scapular rotation, 10°
of glenohumeral)
Humerus
- head of humerus is about 3x's bigger than gleno cavity
- need to keep head of the humerus in the cavity
- head needs to slide down in order to have proper movement
Muscles
- unstable joint—by design
- joint capsule is not very good
- muscles of the rotator cup
- supraspinatus—most commonly injured (most commonly calcified tendon)
- poor blood supply
- raise your hand over your head cuts off the poor blood supply
- get necrosis of the tendon starts and leads to the calcification
- bony restriction—tunnel formed by acromion process and humerus
- fxn is abduction of first 20°
--Ellis answer
- fxn is to hold the head of the humerus in the cavity
- shoulder impingement test
- supraspinatus
- Hitler salute
- Long Head of the biceps
- Pushes down on the head of the humerus when contracts
- Tendon that is in the joint capsule
- Rhematiod arthritis is a problem—destroys the tendon
- Frozen shoulder—tendon destroyed
Stability of the shoulder
- All of the muscles (not just the rotator cuff)
- Nerves control the muscles