Osteoarthritis is adegenerative joint disease that mainly affected on cartilage.
This type ofarthritis will cause pain, swelling, and stiffness of the leg and reduced rangeof motion of leg especially in hip, knee and thumb joint. There are several causesof the osteoarthritis which included older age, sex, overweight, injury andgene. It is more prevalence in people’ age older than 65.Bone is a connectivetissue in the human body that form skeleton and provide movement, support andact as storage for calcium and phosphate. Articular cartilage is also aconnective tissue that located at all diarthrodial joint. It usually provide asmooth surface for joint movement and withstand compressive force.
Thedifferent between bone and articular joint is their component. Firstly, thecomponent 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 ofextracellular matrix and chondrocytes. The extracellular matrix is composed ofproteoglycan, collagen and water.
Unlike the other connective tissue articularcartilage are avascular, alymphatic and aneural tissue. It is nourished anddrained only by diffusion or convection from the surrounding synovial joint. Thefunction of bone is for support, protection, movement, mineral storage andblood cell formation while articular cartilage is mainly help in absorb shockand withstand compressive force. Next is the structure.
There are 2 end and 1shaft on the bone, called as epiphysis the end of bone and diaphysis the shaftof bone. The end of each epiphysis is covered by periosteum. For the structureof cartilage, it contain three distinct zones and one calcified cartilage orzone 4. The normal biomechanics ofthe bone is relatively hard.
The mechanical properties of the bone are the stiffnessand 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, yieldpoint and ultimate failure point. The deformation is not permanent and thestructure will return to the original dimension when the load is removed atelastic region.
Yield point is the elastic limit of the structure, if theloading is continued pass the yield point and into the plastic region and theload is removed, deformation is permanent. If the loading still continued itwill finally reached ultimate failure point. Bone contain stress and straincharacteristics that upon the applied strain rate. The behaviour of the bone isdepend on the loading mode applied, so it is anisotropic and viscoelastic.Therefore, the biomechanical behaviour of bone is affected by the loading modeapplied, direction of loading and frequency of loading. For example, tension,compression loading, shear loading, bending loading and torsion load.
Tensionis when the structure is applied by tensile loading. It provide equal butopposite direction loads on the structure and caused the structure lengthensand 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 oppositedirection but not in the same line with one another. Bending load is thecombination of compression and tension loading. It caused the structure tobend.
The magnitude of stress is directly proportional to distance from naturalaxis of bone. Lastly, torsion load. It applied force are equal, parallel,opposite and perpendicular to the long axis of the structure. It caused thestructure to twist about an axis and produce torque. It is often seen in spiralfracture. In the human body, our bone is bear on those loading. The greater stressour bone can withstand is compression loading.
Articular cartilage isviscoelastic properties. It has both viscous and elastic characteristics. Thereare two type of phenomenon, creep and stress relaxation. Creep phenomenonhappens when the structure is applied by a constant load. The deformation isslow but increase gradually until the creep is reached equilibrium. Next, thestress relaxation. It happens when is applied to a constant deformation.
Itresponse with a rapid, high initial stress followed by a slow and decreasinggradually in order to maintain the deformation. Articular cartilage is undertension, shear and compression force. There are three region in the tensionload, toe, linear and failure region.
Toe region is the alignment of collagenfibres while linear region I stretching of the collagen fibres. When thearticular cartilage under the shear load, it will no pressure changes andintestinal fluid flows occurs. The resistances of the cartilage is depend onthe amount of the collagen present. When compression load is applied, thecartilage help to spread the pressure by the copious exudation of fluid. Fluidflow will stop when reached equilibrium.The reason for abnormalbiomechanics in osteoarthritis are obesity, joint injury and trauma. Obesity, the excess loadingthat applied on the joint cartilage will increased the mechanical stress on thecartilage and affected the chondrocytes which to detect the physical signalfrom their environment by ion channels to extracellular matrix which is help inprotect our cartilage.
The abnormalities of posture, muscle imbalance and poortechnique of exercise will also result an abnormal pressure to the jointcartilage. For example, excessive spinal curvature, posteriorly or anteriorlytilt pelvis, knee valgus and poor hip muscle control during running. The jointinjury and trauma to the joint tissue such as the menisci or ligaments,especially the anterior cruciate ligament. Other than that, ageing is also areason for abnormal biomechanics in osteoarthritis.
One of the composition ofcartilage is proteoglycan. It is a macromolecule which responsible for theresistance of compression force. It is composed by the glycosaminoglycan (GAGs).
There are two types of GAGs, chondroitin sulphate and keratin sulphate. The chondroitinsulphate chains will decrease with aging. ConclusionAs a conclusion,osteoarthritis is a disease of breakdown of joint cartilage. The wear and tearof the joint cartilage are caused by some biomechanics behaviour. We canprevent this diseases by wisely used the biomechanical behaviour.
For example,moderate exercise, exercise loading and others. It can help to increasecartilage matrix synthesis that have the protective effect on the joint.