"Functional Tissue Engineering"

Articular cartilage is the load-bearing tissue within all freely moving joints of mammals, i.e., the diarthrodial joints such as hips, knees, shoulders, etc. All diarthrodial joints must support loads of high magnitude, and function with a remarkably low coefficient friction even with the generally slow reciprocating motions. For example, in the knee or hip, the magnitude of loading may reach higher than 15x body weight, with a normal stress up to 20 MPa acting on its articulating surfaces. Even the shoulder, generally considered as a non-weight bearing joint, but it is actually not a non-load bearing joint. Due to the lever law effect, there is a 20 to 1 disadvantage; thus a 10N load carried by an outstretched arm may be magnified to 200N acting across the glenohumeral joint of the shoulder. Similarly, in the patello-femoral joint (PFJ) of the knee, again with an approximate 20 to 1 disadvantage, the force and stress levels acting across the PFJ may reach similar magnitudes. In addition, these loads are applied, in a normal young vigorous individual, about one million times a year, with a cyclic frequency usually less than 1Hz. For athletes, these operational mechanical requirements are increased many times. It is no wonder that for some unlucky individuals, they develop arthritis in the hip and knee (most frequently); this is a form of failure in these natural bearings.