Biomedical Engineering Reference
In-Depth Information
synovial fluid and increase the hydrostatic pressure within the joint space. A decreased
synovial fluid viscosity will prevent the synovial fluid from protecting the joint during
compressive loading. An increased hydrostatic pressure within the joint space acts to
decrease the mobility of the joint. Combined, the overall effects of synovitis are a loss of
the synovial fluid properties, a possible degradation of the cartilage, and a decreased joint
mobility. Synovitis can be recognized by a swelling of the joints and is diagnosed by tak-
ing a sample of the synovial fluid from the patient. Minor synovitis is common during
arthritis and is generally treated with anti-inflammatory medications.
END OF CHAPTER SUMMARY
11.1
There are 206 bones in the human body that are divided into bones that compose the axial
skeleton and those that compose the appendicular skeleton. All bones have the function to
support and protect the body, store minerals, produce blood cells, and act as levers for
motion. Long bones are divided into three major sections: the epiphysis, the metaphysis,
and the diaphysis. The epiphysis is composed of spongy bone and can withstand loads
from many different directions. The diaphysis is composed of compact bone and can with-
stand loads in one main direction. The metaphysis is the interface of these two regions. The
bone extracellular matrix is composed of a hardened ground substance that is stiff due to
the deposition of calcium salts. Hydroxyapatite crystals are a major component of the
ground substance. Thirty-three percent of bone mass is accounted for by collagen fibers.
There are four types of bone cells that can be identified. These are the osteocytes, the osteo-
blasts, the osteoclasts, and the osteoprogenitor cells. The action of these four cell types
determines the chemical makeup of bone. Bone is composed of a Haversian canal system
structural unit. Each of these units has a central canal that is filled by an artery and vein.
Concentric circles of bone surround this canal and are termed lamellae. Canaliculi run per-
pendicular to the Haversian canal and function to connect bone cells to each other. The
junctions between bones form joints where bones can move around each other. The coeffi-
cient of friction between bones is relatively high, and in fact, bones can wear on each other.
The coefficient of friction is lowered through the presence of cartilage and synovial fluid.
11.2
Synovial fluid fills the space between joints and is produced as an ultra-filtrate of interstitial
fluid. The interstitial fluid is filtered by the synovial membrane and is very similar in com-
position to interstitial fluid, except that there is a significantly higher concentration of pro-
teoglycans. These proteoglycans act to organize water (because they are highly charged) so
that the overall synovial fluid can withstand a higher load. Cartilage also has a property of
organizing and holding synovial fluid within the joint.
11.3
Synovial fluid enters the joint space as a filtrate through the synovial membrane. This mem-
brane is composed of two layers: the synovium and the sub-synovium. The synovium func-
tions to prevent foreign particles from entering the joint space, while the sub-synovium is
composed of an extensive extracellular fiber mesh that acts to filter the interstitial fluid. The
synovial membrane is actually a uni-directional valve because fluid can enter the joint space
through the membrane, but the fluid does not exit the joint space through the synovial
membrane. To model flow through the synovial membrane, we use a modified flux
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