Osteoarthritis.
Last updated Thursday, February 10, 2005
Causes and effectsCauses It is difficult to determine the initial event that leads to the
onset of OA. Nonetheless, all hypotheses associate the OA changes to
the mechanical overloading of the joints.
"Wear and tear" is a widely accepted explanation of the cause of OA.
It should be noted that OA is the result of an interlocking
pathophysiologic malfunction of cartilage and bone metabolism.
Interpreting "wear and tear" of the joints in OA from a biomechanic
perspective allows patients to understand how OA differs from
age-associated degeneration and overuse of the joints. There are ways
to reduce the OA "wear and tear" effects which include weight control,
muscle strengthening exercises, and increased proprioception accuracy.
It is a common view that OA begins as a fibrillation of articular
cartilage, a focal fine roughening of the surface of articular
cartilage, that eventually leads to secondary remodeling of the bony
components of the joint (48). Remodeling refers to the resorption and
formation of bone tissues under the influence of mechanical loading
history on the joints.
An alternative hypothesis suggests that OA originates from the
stiffness of subchondral bone. Normally it is the bone, not the
cartilage, that absorbs most of the impact forces on the extremities.
This "stiff bone" hypothesis suggests that mechanical overloading on
the joints may result in microfractures in subchondral bones underlying
the articular cartilage. The repair of the fractures leads to a net
local increase of the stiffness of the bone. The "stiff bone" provides
less cushion for the overlying cartilage and thus forces the cartilage
to absorb a greater share of the impact energy. The repartition of
forces eventually leads to the degeneration of the articular cartilage.
The relationship between cartilaginous and bony changes in OA is very
complex and intertwined.
A third, and less established hypothesis associates proprioceptive
impairment with knee OA. Proprioception refers to the conscious and
unconscious perception of joint position and movement. Accurate
proprioception is critical to maintain joint stability under dynamic
conditions. Joint stability is important to prevent the wear and tear
from mechanical forces on the extremities.
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