Inman, J Bone Joint Surg Am 1944 - Observations on the Function of the Shoulder Joint
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Observations on the Function of the Shoulder Joint
Inman, Abbott, et al.·J Bone Joint Surg Am·1944·1,367 citations·Biomechanical study
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Inman and colleagues analyzed how the four joints of the shoulder girdle move together to elevate the arm, and which muscle forces drive that motion.
Study of living subjects using roentgenograms, pins drilled into the bones and electromyography from implanted electrodes, with each muscle curve averaged from 4 to 20 observations.
Methods
Model
Living subjects
Roentgenograms and bone pins, including a pin in the clavicle
Implanted‑electrode electromyography
Theoretical force calculations checked against an empirical force model
Loading
Active arm elevation in abduction and in flexion
Held static positions
Outcome measures
Scapulohumeral rhythm
Sternoclavicular and acromioclavicular motion
Muscle and joint forces as multiples of limb weight
Muscle activity patterns on electromyography
Key Findings
After glenohumeral arthrodesis, the authors warned, the maximum range is only 60° of actual motion.
Shoulder elevation was limited to 110° when rotation of the clavicle, tracked by a pin in the bone, was blocked by hand.
Scapular rotation used a second force couple, with the upper trapezius, levator scapulae and upper serratus above and the lower trapezius and lower serratus below.
With the scapula fixed, the arm could be raised to 90° actively and 120° passively, and power fell by a third.
Calculated pressure and friction against the glenoid peaked at 90° of elevation at 10.2 times the weight of the limb.
Subscapularis, infraspinatus and teres minor pulled the humeral head down and, with the deltoid, formed the force couple that elevates the arm, with a calculated pull peaking at 9.6 times limb weight at 60°.
Board pearl
On electromyography the supraspinatus did not initiate abduction but fired with the deltoid throughout the whole arc of elevation.
Authors' conclusion
The studies of joint motion prove conclusively that complete elevation of the arm, in either the coronal or frontal plane, is dependent on free motion in all the joints of the shoulder complex.
Observations on the Function of the Shoulder Joint
Inman, Abbott, et al.·J Bone Joint Surg Am·1944·1,367 citations·Biomechanical study
|
Inman and colleagues analyzed how the four joints of the shoulder girdle move together to elevate the arm, and which muscle forces drive that motion.
Study of living subjects using roentgenograms, pins drilled into the bones and electromyography from implanted electrodes, with each muscle curve averaged from 4 to 20 observations.
Methods
Model
Living subjects
Roentgenograms and bone pins, including a pin in the clavicle
Implanted‑electrode electromyography
Theoretical force calculations checked against an empirical force model
Loading
Active arm elevation in abduction and in flexion
Held static positions
Outcome measures
Scapulohumeral rhythm
Sternoclavicular and acromioclavicular motion
Muscle and joint forces as multiples of limb weight
Muscle activity patterns on electromyography
Key Findings
After glenohumeral arthrodesis, the authors warned, the maximum range is only 60° of actual motion.
Shoulder elevation was limited to 110° when rotation of the clavicle, tracked by a pin in the bone, was blocked by hand.
Scapular rotation used a second force couple, with the upper trapezius, levator scapulae and upper serratus above and the lower trapezius and lower serratus below.
With the scapula fixed, the arm could be raised to 90° actively and 120° passively, and power fell by a third.
Calculated pressure and friction against the glenoid peaked at 90° of elevation at 10.2 times the weight of the limb.
Subscapularis, infraspinatus and teres minor pulled the humeral head down and, with the deltoid, formed the force couple that elevates the arm, with a calculated pull peaking at 9.6 times limb weight at 60°.
Board pearl
On electromyography the supraspinatus did not initiate abduction but fired with the deltoid throughout the whole arc of elevation.
Authors' conclusion
The studies of joint motion prove conclusively that complete elevation of the arm, in either the coronal or frontal plane, is dependent on free motion in all the joints of the shoulder complex.