Osteoarthritis is a name of a medical condition that is the ongoing and the end result of a repeated attempt of the body’s ability to repair and heal itself from sustained and compromised pressure. Osteoarthritis (OA) simply means inflammation (itis) of the boney (osteo) joint (arthro). Although there are several types of joints, joint is a term that usually describes two or more bones coming together to form a specific relationship. Covering the ends of all bones is a smooth, thin and yet, hard piece of plastic called hyaline cartilage.
Specific to the knee and hip joints, there is a thick encasement or shell around the joint that is called the synovial capsule. This shell helps to hold the joint together along with ligaments and tendons. The synovial capsule secretes a dense, slick gel called synovial fluid. This lubricating fluid assists in reducing friction that normally occurs when two surfaces move in relationship to one another.
Also specific to these joints, is a piece of material, precisely shaped for that joint, called articular (meaning joint) cartilage. The presence of this cartilage further separates the ends of the bones and helps to guide the 3 dimensional movements that take place as we go about moving in a day. This articular cartilage also serves as a shock absorber, cushioning the bones from the forces that are passed between and through them.
In the knee, the articular cartilage is referred to as meniscus (menisci is the plural) and in the hip, it is known as labrum. In the knee, the meniscus is the structure that people are referring to when they report that they have a “torn cartilage”. Numerous studies have demonstrated that repair of knee injuries that have removed “torn cartilage” specifically contribute to osteoarthritis as a person ages.
It is the combination of the above elements that prevent the ends of the bones from rubbing against one other. These elements of joint anatomy allow us to experience flexible and nearly frictionless movement. The absence of the articular cartilage, combined with joint laxity or looseness from stretched ligaments or weak muscles, allows the ends of the bones to start to rub against one another. Over time, the wearing away of the hyaline cartilage becomes the most common cause of joint pain and loss of mobility.
Bones are very much living tissue. When they have lost their protective covering and start to rub together, pain receptors in the area will signal when there is too much pressure and that the bone cells are being damaged or hurt. Additionally, the joint will start to swell in attempt to give it more space and to bring in certain cells to start an inflammatory response.
The inflammatory response is like a siren going off in the body signaling that help is needed. Certain cells, in this case, bone cells are being killed, damaged, or threaten and help is needed. The pain and swelling are interpreted by the nervous system to shift the weight bearing forces and/or movement away from the compromised joint. This is when you see a person change how they walk, move, etc. The inflammatory response is also responsible for calling forward certain cells for repair.
Osteoclasts are the garbage collectors that rid the area of damaged bone cells and osteoblasts are the creators of new bone. New bone in a joint is never rebuilt like its original structure and hyaline cartilage can never be remanufactured organically again. New bone is laid down and shaped by movement and is later seen radiographically, i.e. x-rays, as osteophytes (bone spurs) or encapsulated fluid filled cysts embedded in the bone that make a joint susceptible to fracturing. Direct injury/trauma or insidious repetitive microtrauma causes the body’s inflammatory process to be activated and therefore can also be the cause of OA. For specific information on osteoarthritis in the knee joint, see our article, What is Knee Osteoarthritis?
Carol Montgomery is a Physical Therapist, Guild Certified Feldenkrais Practitionercm and Bones for Life® Teacher/Trainer. She has a private practice in Columbus, IN. Montgomery can be reached by email at firstname.lastname@example.org. She offers certification and continuing education programs through www.integrativelearningcenter.org.
1England M. Meniscal tear: a feature of osteoarthritis. Acta Orthop Scand Suppl. 2004; 75:1-45, back cover.