Glenohumeral Suction Cup.
Last updated Thursday, February 10, 2005
Figure 1 - Like a suction cup About the glenohumeral suction cup
The glenohumeral "suction cup" provides stability by virtue of the seal of the labrum and capsule to the humeral head.Suction A suction cup adheres to a smooth surface by expressing the interposed
air or fluid and then forming a seal to the surface. A rubber suction
cup is noncompliant in the center, but becomes more flexible toward its
periphery. Like a suction cup, the glenoid surface has "feathered"
edges which become increasingly flexible with increasing distance from
the center. The center of the glenoid is covered with a relatively thin
layer of articular cartilage. At greater distances from the center, the
articular cartilage becomes thicker, providing greater flexibility.
More peripherally, the glenoid labrum and, finally, the capsule provide
even more flexibility. This graduated flexibility permits the socket to
conform and seal to the smooth humeral articular surface. Compression
of the head into the glenoid fossa expels any intervening fluid so that
a "suction" is produced that resists distraction.Centering the humerus in the glenoid The glenoid suction cup stabilization mechanism is easily
demonstrated in young cadaver shoulders in which the articular
cartilage, glenoid labrum, and joint capsule are compliant. The
magnitude of this stabilizing effect has not been measured.
Like stabilization from adhesion-cohesion, the glenoid suction cup
centers the head of the humerus in the glenoid without muscle action
and is effective in midrange positions in which the capsule and
ligaments are not under tension. The suction cup mechanism is disrupted
in situations where the socket cannot seal to the surface of the
humeral head, such as an avulsion of the glenoid labrum or glenoid
fracture.
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Disclaimer
This resource has been provided by the University of Washington Department of Orthopaedics and Sports Medicine as general information only. This information may not apply to a specific patient. Additional information may be found at http://www.orthop.washington.edu or by contacting the UW Department of Orthopaedics and Sports Medicine.
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