Mechanics of Glenohumeral Instability.

Last updated Friday, February 04, 2005

Adhesion/cohesion

Cohesion and adhesion

Fluids such as water and joint fluid demonstrate the property of cohesion; that is, they tend to stick together. Some surfaces, such as clean glass or articular cartilage, can be wet with water or synovial fluid, meaning that the fluid adheres to them. When two surfaces with adherent fluid are brought in contact, the adhesion of the fluid to the surfaces and the cohesion of the fluids tend to hold the two surfaces together (like two wetted microscope slides). The amount of stability generated by adhesion-cohesion is related to the adhesive and cohesive properties of the joint fluid, the "wetability" of the joint surfaces, and the area of contact between the glenoid socket and the humerus. Joint fluid has the highly desirable properties of

1. having high tensile strength (difficult to pull apart), and
2. having little shear strength (allows easy sliding of the two joint surfaces on each other with low resistance). (Simkin, 1988)

The adhesion/cohesion effect is reduced by any factor that lowers the cohesion of joint fluid (such as in inflammatory joint disease), reduces wetability of the joint surfaces (as may occur in degenerative joint disease), or diminishes the glenohumeral contact area (such as in a displaced articular surface fracture or a congenitally small glenoid). It is also noteworthy that adhesion/cohesion forces do not stabilize a prosthetic shoulder replacement, because metal and polyethylene are insufficiently compliant to provide the necessary near-perfect congruence and because water does not adhere to their surfaces.

How useful was this page or article? This article is rated out of 5 stars (312 ratings). Not useful at all Not very useful Useful Very useful Extremely useful