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A pet does not have to be a senior citizen to require joint care supplements, pain medication, or physical therapy. Degenerative arthritis can result from an injury or can be the result of genetics/joint conformation. If your pet is having stiffness, or poor range of motion in a joint then you will need some education about other joint care options and an understanding of what is happening in your pet's joints, especially if surgery is not an option for one reason or another. The following represents a beginner's overview of joint structure and function so as to provide a foundation for understanding treatment options for the arthritic pet.
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This radiograph shows the two mandibles (lower jaw bones) of a dog. The flashing yellow line shows the "symphysis" joint which joins them
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The vertebral bones are joined together by round disc joints which allow the back to have flexibility
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There are several types of joints within the body. The fibrous discs that separate the back’s vertebrae and allow the back’s flexibility are specialized joints. The two halves of one’s lower jaw are held together by a joint called a “symphysis” which, unlike other joints, is meant to reduce movement, not facilitate it.
The joints we are concerned with when we talk about degenerative arthritis we are talking about “synovial joints” also called “diarthrodial joints.” They consist of two bones and a fibrous capsule holding the two bones together but the joint is far more complicated than just a hinge made of fiber and bone. The two bones surfaces are covered with slippery cartilage that must be able to glide across each other with minimal friction no matter what the patient’s activity level is and they must continue to be able to glide easily in this way repeatedly throughout the patient’s life.
Prevention of the progression of arthritis is all about maintaining the normal structures of the joint. In many cases, this involves providing the biochemical components of these structures as nutritional supplements. Our purpose here is to review what the structures are and what they are made of so that one can better choose supplements and understand what one is giving. For illustrative purposes we will use the knee or "stifle" joint as it is called in animals, as an example. The radiograph at the top of this page shows the bones making up the knee in a dog.
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The articular cartilage surfaces of the joint are the cartilage caps on the ends of the bone. These are the smooth surfaces that must glide across each other. Cartilage is made up of:
- Matrix
The cartilage matrix the material in which the cartilage cells are suspended, (Think of fruit suspended in a "matrix" of jello.) The matrix consists of collagen and proteoglycans. We have all heard of Collagen, the tough support proteins that act as the “steel girders” of the body, holding everything from bone to skin in the shape it is mean to hold. “Proteoglycan” is not a very familiar word to the general public but since most joint nutritional supplements relate to it, it is very important to know what it is. Proteoglycans are the material surrounding the collagen fibers. It consists of a long protein molecule (the “proteo” part of proteoglycan) with strands of what are called
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glycosaminoglycans or GAGs, growing off its sides like the bristles on a hair brush. These GAG bristles allow the proteoglycan molecule to soak up water like a little sponge. It is this sponge characteristic that allows the cartilage to be soft like a mattress, yet slippery like a Slip n’ Slide when the two bones of the joint move across eachother. Two important GAG's are "keratan sulfate" or "chondroitin sulfate," both of which are common nutritional supplements available for joint support in most veterinary hospitals, drug stores, and even grocery stores
- Chondrocytes
These are the actual cells that secrete the cartilage matrix. The matrix is the
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soft (relative to the bone beneath it) material that represents 95% of the cartilage. While the cells represent only a small portion of the cartilage, they must remain healthy so as to produce new matrix, when the old matrix is damaged..
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Many of you reading the word “glycosaminoglycan” may simply let your eye pass over it and not even try to pronounce it in your mind. If you want to know about the nutrition of joint care, though, “glycosaminoglycan” is an important word to know. The three GAGs that can make up a proteoglycan molecule are:
- Chondroitin sulfate
- Keratan sulfate (which is made in the body from a biochemical called “glucosamine”)
- Dermatan sulfate
When you buy a bottle of some sort of joint supplement, the chances are it will contain Chondroitin sulfate and/or Glucosamine. Now you know what you are buying and what these supplements are supposed to do in the body.
This last GAG that one should be familiar with and this is “Hyaluronan.” Unlike the GAGs listed above, it is not sulfated and it is not part of a proteoglycan. It simply binds and connects the proteoglycans together in the matrix. (In the graphic above, it is shown as a sort of a core to which the proteoglycans are attached,) Hyaluronan is also a major component of the joint lubricating fluid which we will review in the next section.
This is the capsule that encloses the joint, creating the structure of the “hinge.” The capsule has an outer tough, fibrous layer and an inner layer that secretes joint fluid, a fluid that provides both nutrition and lubrication to the enclosed joint. The joint capsule must keep unwanted proteins and biochemicals out of the joint and only let the desired nutrients inside. Afterall, the joint must be kept smooth, and the lubricants pure if they are to maintain the joint throughout the patient’s entire lifetime.
The joint capsule has two types of cells: Type A Synoviocytes and Type B Synoviocytes. The Type A cells are all about removing impurities and cleaning up debris. Type B cells produce Hyaluronan (mentioned above), an important lubricant in the joint.
When there is injury or simply poor conformation, the cartilage becomes roughened and can chip, flake off, or even wear down. The joint capsule becomes inflamed and thickened and no longer functions normally. Impurities enter the joint, the lubricating fluid loses its natural properties and ultimately a progressively abnormal and painful joint is created. In providing treatment, our goal is to alleviate the pain and inflammation and provide the biochemical building blocks that allow the joint to heal itself. In the next sections we will review medications, supplements, and even exercises that may help with the arthritic patient.
Page last updated: 1/29/08
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THE JOINT CAPSULE OR “SYNOVIAL MEMBRANE”