Shoulder Joint Applied Biomechanics

convex/concave rule

elbow rolls, dot glides

convex on concave movement

rolls and slides in other directions

concave on convex movement

concave surface rolls and slides in similar directions

what kind of a joint is the sternoclavicular joint?

basilar/saddle

how many degrees of the freedom does the SC joint have?

3: elevation/depression (frontal), protraction/retraction (horizontal), posterior rotation (saggital)

SC elevation

concave clavicle rolls superior and slides inferior

SC depression

convex clavicle rolls inferior and slides superior

SC protraction

concave clavicle rolls/slides anteriorly

SC retraction

concave clavicle rolls/slides posteriorly

SC posterior spin

as one raises arm overhead, superior clavicle rotates posteriorly 20-35 degrees

how many degrees of freedom does the acriomioclavicular joint have?

3: upward/downward rotation, int/ext rot (horizontal), ant/post tilting (saggital)

resting posture of the scapula

10 degrees of anterior tilt, 5-10 degrees of upward rotation, 30-40 degrees of int rot

how many degrees of freedom does the scapulothoracic joint have?

3: elevation/depression, protraction/retraction, upward/downward rotation

ST elevation

SC elevation + AC downward rotation

ST depression

SC depression + AC upward rotation

ST protraction

SC protraction + AC int rot

ST retraction

SC retraction + AC ext rot

ST upward rot

SC elevation + AC upward rot

ST downward rot

SC depression + AC downward rot

how many degrees of freedom does the glenohumeral joint have?

4: flex/ext, abd/add, int/ext rot, horizontal abd/add

GH abduction

convex humeral head rolls superior with inferior sliding

GH adduction

convex humeral head rolls inferior with superior sliding

GH flex/ext

spinning of humeral head

GH external rotation

convex humeral head rolls posteriorly and slides anteriorly on glenoid fossa

GH internal rotation

convex humeral head rolls anteriorly and slides posteriorly on glenoid fossa

scapulohumeral rhythm

for every 3 degrees of shoulder abduction, 2 degrees occur by GH abduction and I degree occurs by ST upward rot

what muscles upwardly rotate the scapula when abducting the arm?

lower/upper traps, serratus anterior

what is the role of the middle trapezius?

strong retractor to neutralize serratus anterior's role as a strong protractor

rotator cuff force couple muscles

deltoid (abduction of humerus), supraspinatus (horizontal compression stabilization force), subscapularis (inferior force), infraspinatus and teres minor (inferior force and externally rotate humerus)

what is a potential issue that the deltoid runs into when abducting the humerus?

humeral head is stopped by coracoacromial boney arch

why do infraspinatus and teres minor externally rotate the humerus?

so that the greater tubercle of the humerus can clear the acromion process

why is the coracoclavicular ligament important for the sternoclavicular joint?

the ligament attaches to the posterior side of the clavicle so that in scapular upward rotation, the posterior spin of the scapula allows slack on the ligament