Shoulder abduction moment arms in three clinically  important positions.
The abduction moment arms of 4 shoulder muscles were calculated in clinically important positions to evaluate the best test situation for the supraspinatus based on its mechanical advantage.Moment arms of the supraspinatus, infraspinatus, and middle and anterior deltoid in 18 individuals were computed using individual magnetic resonance imaging data and a computer-assisted design tool for simulation. Three tests with the arm in the neutral position (arm hanging on side), at 90 of scaption,and at 90 of scaption and full internal humeral rotation (Jobe test) were investigated. The supraspinatushas a greater mechanical advantage vs the other tested muscles in the neutral arm position. In the Jobe position, the supraspinatus' abduction moment arm is reduced with increased internal humeral rotation.Comparing these results with the literature indicates that this new method is adequate for calculation of moment arms and may be used in any desired joint configuration.
Ruckstuhl
Heidi
H
Department of Mechanical and Process Engineering, Institute for Biomechanics, Zurich, Switzerland. heidi.ruckstuhl@gmail.com
Krzycki
Jacek
J
Petrou
Nassos
N
Favre
Philippe
P
Horn
Tamara
T
Schmid
Stefan
S
Stussi
Edgar
E
D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D010264:Paraplegia; D016059:Range of Motion, Articular / Q000502:physiology*; D012680:Sensitivity and Specificity; D012785:Shoulder Joint / Q000473:pathology* / Q000502:physiology*