About the Mechanics of Shoulder Stability.
Last updated Thursday, February 10, 2005
Figure 6 - Glenoid center line Figure 8 - Glenohumeral translation Definitions
Precise definitions are necessary in the discussion of glenohumeral stability.What is the glenoid center line? The glenoid center line is the line perpendicular to the surface of the glenoid fossa at its midpoint (see figure 6).What is the net humeral joint reaction force? The net humeral joint reaction force is the vector sum of all forces
acting on the humeral head relative to the glenoid fossa. It is this
force that needs to be stabilized at the glenohumeral joint. This force
includes component forces applied to the humerus by muscles, capsule,
and ligaments as well as by external factors such as gravity, contact
with objects, and inertia (see figure 7).
What is glenohumeral translation? Glenohumeral translation is movement of the center of the humeral head with respect to the face of the glenoid (see figure 8).What is glenohumeral translational laxity? Glenohumeral translational laxity is the translation observed on
examination of the joint. A substantial amount of laxity is
characteristic of normal glenohumeral joints.What is glenohumeral stability? Glenohumeral stability is the ability to maintain the humeral head centered in the glenoid fossa.
What is glenohumeral instability? Glenohumeral instability is the inability to maintain the humeral head centered in the glenoid fossa.What is glenohumeral apprehension? Glenohumeral apprehension is the sense of impending instability in certain glenohumeral positions.What is traumatic glenohumeral instability? Traumatic instability is instability that arises from an injury of
sufficient magnitude to tear the glenohumeral capsule, ligaments, or
rotator cuff or to produce a fracture of the humerus or glenoid.What is atraumatic glenohumeral instability? Atraumatic instability is instability that arises without significant trauma.
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