Scapular inclination and glenohumeral joint stability: a cadaveric study.
BACKGROUND
In shoulders with multidirectional instability, translation of the humeral head on the glenoid is increased in the midrange because of the following three reasons: the increased retroversion, a hypoplastic posteroinferior rim, and decreased scapular abduction during arm elevation. This study aimed to clarify the relationship between glenoid inclination and glenohumeral joint stability.


METHODS
Nine fresh-frozen cadaveric shoulders were tested. With a 50-N compressive load, the translation force was measured in the 3-o'clock, 6-o'clock, 9-o'clock, and 12-o'clock directions by using a tilt of 0 degrees , 5 degrees , 10 degrees , 15 degrees , and 20 degrees . When the glenoid was tilted in one direction, the translation force was measured in the direction of inclination and in the opposite direction. The stability ratio was then calculated.


RESULTS
The stability ratio in the 3-o'clock direction significantly decreased with a tilt of more than 5 degrees in the 3-o'clock direction. The stability ratio in the 9-o'clock direction significantly decreased with a tilt of more than 15 degrees in the 9-o'clock direction and significantly increased with a tilt of more than 5 degrees in the 3-o'clock direction. The stability ratio in the 6-o'clock direction significantly increased with a tilt of more than 10 degrees in the 6-o'clock direction.


CONCLUSIONS
The posterior and inferior stability increased with an anterior tilt of more than 5 degrees and with a superior tilt of 10 degrees , respectively. The anterior and posterior stability decreased with an anterior tilt of 5 degrees and with a posterior tilt of 15 degrees , respectively.
Kikuchi
Kazuma
K
Division of Orthopedic Surgery, Department of Neuro and Locomotor Science, Akita University School of Medicine, Akita, Japan.
Itoi
Eiji
E
Yamamoto
Nobuyuki
N
Seki
Nobutoshi
N
Abe
Hidekazu
H
Minagawa
Hiroshi
H
Shimada
Yoichi
Y
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000209:etiology* / Q000503:physiopathology*; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D012540:Scapula / Q000503:physiopathology*; D012785:Shoulder Joint; D016474:Weight-Bearing / Q000502:physiology