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HomeIntroductionRequirements for shoulder stabilityMoviesDefinitionsGlenoid center line Net humeral joint reaction force Glenohumeral translation Glenohumeral translational laxity Glenohumeral stability Glenohumeral instability Glenohumeral apprehension Traumatic glenohumeral instability Atraumatic glenohumeral instability Conclusion

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About the Mechanics of Shoulder Stability.

Last updated Thursday, February 10, 2005

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Figure 6 - Glenoid center line

Figure 7

Figure 8 - Glenohumeral translation

Definitions

Precise definitions are necessary in the discussion of glenohumeral stability.

Glenoid center line

The glenoid center line is the line perpendicular to the surface of the glenoid fossa at its midpoint (see figure 6).

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).

Glenohumeral translation

Glenohumeral translation is movement of the center of the humeral head with respect to the face of the glenoid (see figure 8).

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.

Glenohumeral stability

Glenohumeral stability is the ability to maintain the humeral head centered in the glenoid fossa.

Glenohumeral instability

Glenohumeral instability is the inability to maintain the humeral head centered in the glenoid fossa.

Glenohumeral apprehension

Glenohumeral apprehension is the sense of impending instability in certain glenohumeral positions.

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.

Atraumatic glenohumeral instability

Atraumatic instability is instability that arises without significant trauma.

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