Dynamic stabilizing function of the deltoid muscle in shoulders with anterior instability.
BACKGROUND
The stabilizing role of the deltoid muscle has not been extensively studied.


OBJECTIVE
To study the contribution of the deltoid muscle to anterior stability of the shoulder.


METHODS
Controlled laboratory study.


METHODS
We used nine fresh cadaveric shoulders with the arm at 90 degrees of abduction and 90 degrees of external rotation. The position of the humeral head was monitored by an electromagnetic tracking device with 0 and 1.5 kg of anterior translation force; with 0, 1, 3, and 5 kg of force applied to each of the anterior, middle, and posterior portions of the deltoid muscle; and with the capsule intact, vented, and with a simulated Bankart lesion.


RESULTS
With the capsule intact, anterior displacement was significantly reduced by application of load to the middle deltoid muscle. After the capsule was vented, load application to the anterior, middle, or posterior deltoid muscle significantly reduced anterior displacement. With a simulated Bankart lesion, effects of muscle loading were most apparent: anterior displacement was significantly reduced with loading of each muscle portion.


CONCLUSIONS
The deltoid muscle is an anterior stabilizer of the glenohumeral joint with the arm in abduction and external rotation.


CONCLUSIONS
The stabilizing function of the deltoid muscle takes on more importance as the shoulder becomes unstable.
Kido
Tadato
T
Orthopedic Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic, Rochester, Minnesota 55905, USA.
Itoi
Eiji
E
Lee
Seok-Beom
SB
Neale
Patricia G
PG
An
Kai-Nan
KN
D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular; D012399:Rotation; D012785:Shoulder Joint / Q000502:physiology*