Table 1.

Causes of thinning of the articular cartilage

Cause	Mechanism	Reversible?
Osteoarthritis	Proteolytic degradation of matrix	No, except by regeneration
Atrophy	Reduced synthesis of proteoglycan; a mechanoadaptive response to reduced load	Yes, weeks–months
Cartilage compression	Water extrusion from matrix due to compression	Yes, minutes–hours
Apparent reduction in joint space (‘pseudo thinning’)	Migration of tidemark or meniscal extrusion	Unknown