* Ball and Socket Joints
* Hinge Joints
* Pivot Joints
* Condyloid Joints
* Saddle Joints
* Gliding Joints
Tuesday, 8 September 2009
Articular Cartilage - Role in Canine Arthritis
The main functions of articular cartilage are to facilitate the movement of one bone against another and to act as a ‘shock abosorber’. It has a very low friction co-efficient and has properties that make it able to withstand enormous forces. It is a smooth, white with a bluish tinge, glistening tissue and is also commonly known as hyaline cartilage.
The glassy appearance of articular cartilage is due to two factors:
1. the high water content (70% in adults and up to 90% in newborns)
2. the fine structure of its collagen fibril network, which is made up of the following:
* Collagen – 50%
* Proteoglycans – 35%
* Glycoproteins – 10%
* Minerals – 3%
* Lipids – 1%
* Chondrocytes – 1-2%
Most (85-90%) of the collagen in articular cartilage is type II collagen and this provides the tensile stiffness. There are also small amounts of types VI, IX, XI, XII and XIV. Type IX collagen is linked to type II and is important in stabilising the three-dimensional organisation of the matrix.
The glassy appearance of articular cartilage is due to two factors:
1. the high water content (70% in adults and up to 90% in newborns)
2. the fine structure of its collagen fibril network, which is made up of the following:
* Collagen – 50%
* Proteoglycans – 35%
* Glycoproteins – 10%
* Minerals – 3%
* Lipids – 1%
* Chondrocytes – 1-2%
Most (85-90%) of the collagen in articular cartilage is type II collagen and this provides the tensile stiffness. There are also small amounts of types VI, IX, XI, XII and XIV. Type IX collagen is linked to type II and is important in stabilising the three-dimensional organisation of the matrix.
Synovial Fluid Info - Canine Arthritis
Synovial fluid functions to lubricate synovial joints thus reducing friction and enhancing ease of movement. It is a viscous (thick) fluid, with a consistency similar to that of a raw egg white. In fact part of the name ‘synovial’ comes from the latin for egg – ‘ovum’.
Synovial fluid is an ultrafiltrate of plasma (ultra-filtration is the process of forcing a liquid against a semi-permeable membrane, causing the liquid and some smaller particles to pass through the membrane. Bigger particles are retained on the original side of the membrane – think of a balloon, filled with water and rice grains, with pin pricks in it. When you squeeze the balloon, the pin prick holes get bigger allowing more water and some grains of rice to pass through them) and therefore most ions and molecules equilibrate to starling forces. (An explanation of starling forces is beyond the scope of this blog, but for more information have a look at the following link: http://en.wikipedia.org/wiki/Starling_forces )
The exception to this rule is hyaluronan, which reaches high concentrations in synovial fluid (0.1 – 5.0 mg/ml). Hyaluronan is a polysaccharide which is synthesized by type B synoviocytes (in the synovial membrane). The synthesis is catalyzed by the enzyme hyaluronan synthetase and occurs at the plasma membrane of synoviocytes. The hyaluronan is extruded to the extracellular space during elongation. Hyaluronan is a large, coiling molecule which overlaps and becomes tangled with other hyaluronan molecules. It is this entanglement that produces the high viscosity of synovial fluid.
The viscous nature of synovial fluid allows it to support transient shear stresses and absorb some of the energy generated by movement. High shear stresses and rapid movement decrease viscosity. This shear thinning behaviour under movement is known as “thixotropy”.
Synovial fluid is an ultrafiltrate of plasma (ultra-filtration is the process of forcing a liquid against a semi-permeable membrane, causing the liquid and some smaller particles to pass through the membrane. Bigger particles are retained on the original side of the membrane – think of a balloon, filled with water and rice grains, with pin pricks in it. When you squeeze the balloon, the pin prick holes get bigger allowing more water and some grains of rice to pass through them) and therefore most ions and molecules equilibrate to starling forces. (An explanation of starling forces is beyond the scope of this blog, but for more information have a look at the following link: http://en.wikipedia.org/wiki/Starling_forces )
The exception to this rule is hyaluronan, which reaches high concentrations in synovial fluid (0.1 – 5.0 mg/ml). Hyaluronan is a polysaccharide which is synthesized by type B synoviocytes (in the synovial membrane). The synthesis is catalyzed by the enzyme hyaluronan synthetase and occurs at the plasma membrane of synoviocytes. The hyaluronan is extruded to the extracellular space during elongation. Hyaluronan is a large, coiling molecule which overlaps and becomes tangled with other hyaluronan molecules. It is this entanglement that produces the high viscosity of synovial fluid.
The viscous nature of synovial fluid allows it to support transient shear stresses and absorb some of the energy generated by movement. High shear stresses and rapid movement decrease viscosity. This shear thinning behaviour under movement is known as “thixotropy”.
The Synovial Joint in Dogs - Structure
There are 3 components of a synovial joint:
• The Fibrous Capsule (Articular Capsule)
• Synovial Membrane
• Articular Cartilage
The fibrous capsule consists of 2 layers;
• a thick white fibrous outer layer which is known as the stratum fibrosum and
• an inner layer called the stratum synoviale (or synovial membrane or synovium), which is in contact with the synovial fluid.
The fibrous capsule is continuous with the periosteum of bone. It does not have any blood or lymph supply (avasuclar), but is highly innervated (which helps to explain why joint injuries can be so painful!)
The articular cartilage covers the epiphyses of the bone and provides resistance to load and shock The synovial membrane is the inner layer of the fibrous capsule.
The synovial membrane lines the synovial cavity where articular cartilage is not present. The synovial membrane is 1-4 synoviocytes (cells that make up the synovial membrane) thick and these synoviocytes can have both secretory (type B) and phagocytic (type A) functions. Type B synoviocytes synthesize and secrete Hyaluronan and Lubricin (a surface acting glycoprotein) into the synovial fluid.
- Dr Caroline
• The Fibrous Capsule (Articular Capsule)
• Synovial Membrane
• Articular Cartilage
The fibrous capsule consists of 2 layers;
• a thick white fibrous outer layer which is known as the stratum fibrosum and
• an inner layer called the stratum synoviale (or synovial membrane or synovium), which is in contact with the synovial fluid.
The fibrous capsule is continuous with the periosteum of bone. It does not have any blood or lymph supply (avasuclar), but is highly innervated (which helps to explain why joint injuries can be so painful!)
The articular cartilage covers the epiphyses of the bone and provides resistance to load and shock The synovial membrane is the inner layer of the fibrous capsule.
The synovial membrane lines the synovial cavity where articular cartilage is not present. The synovial membrane is 1-4 synoviocytes (cells that make up the synovial membrane) thick and these synoviocytes can have both secretory (type B) and phagocytic (type A) functions. Type B synoviocytes synthesize and secrete Hyaluronan and Lubricin (a surface acting glycoprotein) into the synovial fluid.
- Dr Caroline
Predisposition to Canine Arthritis
One of the major preventable factors which may predispose your dog to developing canine arthritis is being overweight or obese. Obesity leads to far greater than normal forces being applied to joints during periods of moderate to intense exercise. Actions such as jumping out of the car boot for fat dogs can lead to severe joint trauma. Obesity is particularly problematic in larger breeds of dogs, as the weight their joints have to bear is already so high. For more information on obesity and its role in canine arthritis, have a look at the section on conservative treatment on the treatment page.
Genetics can also play a part in the development of canine osteoarthritis, but it is a polygenic trait, so modes of inheritance are not as straightforward as they are with many other diseases.
- Dr Caroline
Genetics can also play a part in the development of canine osteoarthritis, but it is a polygenic trait, so modes of inheritance are not as straightforward as they are with many other diseases.
- Dr Caroline
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