Osteoarthritis support and act as storage for calcium

Osteoarthritis is a
degenerative joint disease that mainly affected on cartilage. This type of
arthritis will cause pain, swelling, and stiffness of the leg and reduced range
of motion of leg especially in hip, knee and thumb joint. There are several causes
of the osteoarthritis which included older age, sex, overweight, injury and
gene. It is more prevalence in people’ age older than 65.Bone is a connective
tissue in the human body that form skeleton and provide movement, support and
act as storage for calcium and phosphate. Articular cartilage is also a
connective tissue that located at all diarthrodial joint. It usually provide a
smooth surface for joint movement and withstand compressive force. The
different between bone and articular joint is their component. Firstly, the
component of bone and articular cartilage. Bone are formed by the osteoblast,
made up of osteocytes and osteoclasts .It is highly vascularized.  The articular cartilage is composed of
extracellular matrix and chondrocytes. The extracellular matrix is composed of
proteoglycan, collagen and water. Unlike the other connective tissue articular
cartilage are avascular, alymphatic and aneural tissue. It is nourished and
drained only by diffusion or convection from the surrounding synovial joint. The
function of bone is for support, protection, movement, mineral storage and
blood cell formation while articular cartilage is mainly help in absorb shock
and withstand compressive force. Next is the structure. There are 2 end and 1
shaft on the bone, called as epiphysis the end of bone and diaphysis the shaft
of bone. The end of each epiphysis is covered by periosteum. For the structure
of cartilage, it contain three distinct zones and one calcified cartilage or
zone 4.


The normal biomechanics of
the bone is relatively hard. The mechanical properties of the bone are the stiffness
and strength of the bone. It can be examining by the load-deformation curve.
There are two region and two point, like elastic region, plastic region, yield
point and ultimate failure point. The deformation is not permanent and the
structure will return to the original dimension when the load is removed at
elastic region. Yield point is the elastic limit of the structure, if the
loading is continued pass the yield point and into the plastic region and the
load is removed, deformation is permanent. If the loading still continued it
will finally reached ultimate failure point. Bone contain stress and strain
characteristics that upon the applied strain rate. The behaviour of the bone is
depend on the loading mode applied, so it is anisotropic and viscoelastic.
Therefore, the biomechanical behaviour of bone is affected by the loading mode
applied, direction of loading and frequency of loading. For example, tension,
compression loading, shear loading, bending loading and torsion load. Tension
is when the structure is applied by tensile loading. It provide equal but
opposite direction loads on the structure and caused the structure lengthens
and narrows. Compression loading is load that applied on structure in an equal,
act in the line towards each other but at the oppiste side of the structure.
Shear loading is when the applied force is equal, parallel and in opposite
direction but not in the same line with one another. Bending load is the
combination of compression and tension loading. It caused the structure to
bend. The magnitude of stress is directly proportional to distance from natural
axis of bone. Lastly, torsion load. It applied force are equal, parallel,
opposite and perpendicular to the long axis of the structure. It caused the
structure to twist about an axis and produce torque. It is often seen in spiral
fracture. In the human body, our bone is bear on those loading. The greater stress
our bone can withstand is compression loading.

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Articular cartilage is
viscoelastic properties. It has both viscous and elastic characteristics. There
are two type of phenomenon, creep and stress relaxation. Creep phenomenon
happens when the structure is applied by a constant load. The deformation is
slow but increase gradually until the creep is reached equilibrium. Next, the
stress relaxation. It happens when is applied to a constant deformation. It
response with a rapid, high initial stress followed by a slow and decreasing
gradually in order to maintain the deformation. Articular cartilage is under
tension, shear and compression force. There are three region in the tension
load, toe, linear and failure region. Toe region is the alignment of collagen
fibres while linear region I stretching of the collagen fibres. When the
articular cartilage under the shear load, it will no pressure changes and
intestinal fluid flows occurs. The resistances of the cartilage is depend on
the amount of the collagen present. When compression load is applied, the
cartilage help to spread the pressure by the copious exudation of fluid. Fluid
flow will stop when reached equilibrium.

The reason for abnormal
biomechanics in osteoarthritis are obesity, joint injury and trauma. Obesity, the excess loading
that applied on the joint cartilage will increased the mechanical stress on the
cartilage and affected the chondrocytes which to detect the physical signal
from their environment by ion channels to extracellular matrix which is help in
protect our cartilage. The abnormalities of posture, muscle imbalance and poor
technique of exercise will also result an abnormal pressure to the joint
cartilage. For example, excessive spinal curvature, posteriorly or anteriorly
tilt pelvis, knee valgus and poor hip muscle control during running. The joint
injury and trauma to the joint tissue such as the menisci or ligaments,
especially the anterior cruciate ligament. Other than that, ageing is also a
reason for abnormal biomechanics in osteoarthritis. One of the composition of
cartilage is proteoglycan. It is a macromolecule which responsible for the
resistance of compression force. It is composed by the glycosaminoglycan (GAGs).
There are two types of GAGs, chondroitin sulphate and keratin sulphate. The chondroitin
sulphate chains will decrease with aging.



As a conclusion,
osteoarthritis is a disease of breakdown of joint cartilage. The wear and tear
of the joint cartilage are caused by some biomechanics behaviour. We can
prevent this diseases by wisely used the biomechanical behaviour. For example,
moderate exercise, exercise loading and others. It can help to increase
cartilage matrix synthesis that have the protective effect on the joint.