Lubrication of Joints - Biofluidmechanics: An Introduction to Fluid Mechanics Macrocirculation and Microcirculation - page 307

from the cartilage. This information can be built into a relationship for the formation rate
of cartilage used in Equation 11.1 . Stress and strain are defined as

F
A

σ 5 ð 11 : 6 Þ

and:

ε 5 E 5 Δ l ð 11 : 7 Þ

l

respectively.

Example
Using the results obtained from the previous example, calculate the cartilage stress and the
change in length of cartilage on the femoral head. Assume that the cross-sectional area of the cartilage
is 150 cm 2 , that the elastic modulus for cartilage is 25 MPa, and that the cartilage thickness is 1.5 mm.
Also assume that all of the forces acting on the femoral head are transmitted through the cartilage.

Solution

F
A 5

11 011 N

150 cm 2 5

;

σ 5 0 : 734 MPa

ε 5 E 5

0 : 734 MPa

25 MPa

0 : 029

5

Δl 5 εl 5 0 : 029 ð 1 : 5mm Þ 5 0 : 044 m

This suggests that the thickness of the cartilage changes from 1.5 mm to 1.456 mm in thickness.

11.5 DISEASE CONDITIONS

11.5.1 Synovitis
Synovitis is a condition that is characterized by an inflammation of the synovial mem-
brane. As discussed above, the synovial fluid is secreted by the synovial membrane, and it
is this process that is disrupted during inflammation of the synovial membrane. During
synovitis, the permeability of the synovial membrane increases, allowing white blood cells
into the joint space to defend against the infection. White blood cells in the joint space
release enzymes that can degrade the cartilage if the condition persists for an extended
period of time. This will cause a great deal of pain and the overall lubrication of the joint
will be reduced because 1) the cartilage will not store as much synovial fluid as normal,
2) the shock-absorbing function of the cartilage/synovial fluid will be reduced, and
3) bone may come into contact with bone. A secondary effect associated with synovial
membrane breakdown is an increase in interstitial fluid movement into the joint space.
Increases in interstitial fluid within the joint space will decrease the viscosity of the