This is the common perception of Knee Osteoarthritis in our country where Primary Hip Osteoarthritis is rare. However in the recent past, it has been realized that not only are the elderly at definite risk of Osteoarthritis but many more of the middle aged and even young. Osteoarthritis is the commonest form of joint disease (arthritis) and is a leading cause of disability in older individuals in many countries. It is the common perception that wear and tear inevitable with aging alone leads to Osteoarthritis, but this is not the whole truth. As we shall see not only the elderly, but others are also vulnerable to Osteoarthritis.
Osteoarthritis (OA) in peripheral joints, most frequently involves the knee joint, and the disease may affect one or more of the three compartments of the knee. The knee joint acts to transfer force from the thigh muscles to the leg to move the body. Loads exerted on the surfaces of the knee during normal daily activities are two to seven times the body weight. It is therefore no wonder that the knee is so vulnerable to wear and tear (Osteoarthritis). Osteo-arthritic changes in the joint decrease the effectiveness of load transfer during these activities. Overall health is impaired and Knee OA has been to shown to account for more limitations in walking, stair climbing or other daily activities than any other disease. The form of the disease in the elderly is called primary osteoarthritis whereas the affliction of the young and middle aged is called Secondary osteoarthritis. Let us take a look at the risk factors for developing secondary osteoarthritis, which encompasses other age groups of people in the general population.
These are of two categories, General or systemic and local risks.
Man along with two more mammals, the Elephant and the bear are the only animals to have straight knees. Evolutionarily straight knees are invaluable to minimize energy expenditure during walking so that the body does not tilt from side to side as it would do if the knees were bent in a two legged creature. The price or side effect of the erect posture is weight transmission occurring through the inner half of the knee joint. Therefore the inner half of the knee is susceptible to wear in the normal course of time.
These play a major role in a generalized form of the disease known to affect some communities and families. Research is on to identify the exact genetic location that increases the susceptibility to OA.
Many degenerative diseases like Osteoarthritis are the result of tissue damage from “Free Oxygen radical” attack. Normal cartilage cells are known to reduce free radicals. Anti oxidants such as Vitamin A, C and E have the potential to protect against such tissue damage. It was found in a study that people consuming High amounts of Vitamin C have a 60- 70 per cent reduction in risk for progressive OA. High vitamin C intake levels were also found to be associated with a reduced risk for knee pain according to the same study.
Vitamin D plays an important role in bone mineralization. Results from the above study show that high levels are protective against progression of disease.
Bone mineral density
About three decades ago surgeons removing the head of the upper end of the thigh bone from elderly patients with hip fractures in the operation of partial hip replacement, observed that the end bone rarely showed arthritic changes. Since then, many studies have confirmed the inverse relationship between Osteoporosis and Osteoarthritis. Currently research is on to determine if the medicines prescribed for Osteoporosis such as Calcitonin and Bisphoshphonates prevent the x- ray changes of OA and prevent cartilage breakdown.
Female hormonal deficiency (estrogen)
The incidence of Knee OA increases in Post menopausal women suggesting that estrogen deficiency might be a risk factor and that post menopausal women are more susceptible to osteoarthritis. Despite the obvious correlation, more research is needed to understand the relationships between bone mineral density, estrogen and OA. As females are the preponderant sex to suffer from OA knees, Female specific Knee implants or Prostheses have been developed for a Total knee replacement as the majority of people (two thirds) undergoing a knee replacement are women.
Local risk factors
Increased body weight contributes to the increased load transmitted across the weight bearing knees by a factor of three to seven times the body weight and leads to accelerated wear of the articular cartilage. The relationship between obesity and Osteoarthritis is stronger for bilateral than unilateral disease and is greater in women than men. Since the load transmitted to the knees varies between three to seven fold the body weight, one fold reduction of weight leads to a three to seven fold decreased pressure on the knees. In addition the knee alignment may affect the impact of body weight on the knee joint. Knees with bow legs are more stressed by body weight resulting in more severe inner compartment arthritis.
There is no evidence that participation in light or moderate levels of physical activity (walking, running, dancing, cycling, gardening, and outdoor sports) throughout the life cycle will increase an individual’s risk of developing knee OA. This means that even middle aged people can safely participate in these activities without risk of developing osteoarthritis.
However participation in high intensity contact sports is strongly linked to development of knee OA in elite athletes. Many tennis players, runners, professional soccer players are more likely to suffer from knee arthritis and Patello-femoral OA than age matched controls.
Men in occupations that require repetitive overuse of the knee joint for example, carpenters, painters, miners, dock workers have an increased risk of developing knee OA. Crouching, kneeling, squatting, climbing stairs and lifting heavy loads all cause abnormal joint loading across the knee joint and lead to cartilage damage. The risk factors are similar in both men and women.
Several studies in Europe and America have confirmed that knee injury is a strong predictor for the development of knee OA. Most Knee injuries involve the ACL (Anterior cruciate ligament and ACL rupture is often associated with meniscal damage or a tear in the medial collateral ligament. ACL injuries occur after two wheeler accidents, domestic and outdoor accidents. Both ACL deficiency and meniscal rupture are strongly linked to early degenerative arthritic changes. Although at present it is not clear to what extent the common operation of ACL reconstruction can delay the onset of arthritis, some studies show that early ACL reconstruction with meniscal preservation and not menisectomy provides the greatest protection. A poor outcome after knee injuries is seen in patients who have undergone a partial or total menisectomy an operation which is commonly performed by surgeons. Meniscal suture and Meniscal transplant are ways to protect against osteoarthritis. The former operation is available but the later is yet to kick off from early teething problems. A meniscal transplant facility was announced in Chennai last year but supply of grafts has not been forthcoming.
Mechanical environment of the knees
It is easy to comprehend how any joint or bearing can wear out quickly by understanding what happens to your car tyres if the alignment and balancing is not perfect or if the pressure is more or less. The treads on the overloaded portion of the tyre wear out more. The same analogy applies to the knees. Knees which have a bend like the one shown in the picture will wear out faster. Increased joint laxity an accompaniment of age contributes to OA.
It is a well known observation that people with OA have weakness of the quadriceps muscles. It was assumed that decreased muscle strength is the result of disuse atrophy secondary to knee pain; however it has been noted recently that many patients with asymptomatic knee arthritis have weak muscles. Therefore it makes sense to develop the thigh muscles to prevent arthritis or ameliorate the symptoms after its development, but is to be noted that increasing muscle strength will not arrest progression of the disease.
In summary Knee Osteoarthritis once considered an inevitable consequence of aging is now recognized to be multi-factorial, resulting from the interaction of a variety of general and local factors like age, genetic predisposition, obesity, trauma and mechanical properties of the joint. The traditional surgical treatment of OA “a total knee replacement” is the best long term cost effective solution. However other operations like an osteotomy to correct the alignment of the bones around the knee, ACL reconstruction, cartilage surgery, medications are available to different affected groups of patients. They will not condemn the patient to developing Osteoarthritis in earlier age and become a candidate for a total knee replacement.