Exercise Neither Causes Nor Prevents Knee Osteoarthritis

BOSTON, Jan 31 -- Insofar as pain-free knees are concerned, recreational exercise is orthopedically irrelevant to middle-age and older persons, researchers here reported.

Among those without knee osteoarthritis in the first place, recreational exercise neither caused it to develop nor protected against it, they found in a study of nearly 1,300 participants.

Even though overweight patients in the study had an increased risk of developing knee osteoarthritis, physical activity -- walking, jogging, or other self-reported activity -- did not contribute to this risk, David Felson, M.D., of Boston University, and colleagues. reported in the February issue of Arthritis Care and Research.

Furthermore, despite previous studies that suggested that exercise might prevent loss of joint space, there was no evidence that physical activity benefits cartilage, they said.

Although regular exercise is recommended for middle-age and older persons, its effect on the development of osteoarthritis in older persons, especially those who are overweight, has been unclear, Dr. Felson said.

In a study to evaluate the long-term effect of recreational exercise on knee osteoarthritis, 1,279 participants (mean age at 1993-1994 baseline, 53.2 years) from the Framingham Offspring cohort were asked about recreational activities including walking or jogging for exercise and working up a sweat. They were also asked to compare their activity levels with others.

Participants (age range 26-81 years) were then asked about knee pain, and weight-bearing anteroposterior and lateral knee radiographs were obtained.

Knees with osteoarthritis even in one knee at baseline were excluded, while the investigators focused on three knee-specific outcomes: new radiographic osteoarthritis, symptomatic disease, and tibiofemoral joint-space loss.

Approximately nine years later (2002-2005), the subjects were reexamined. Radiographs were read for osteoarthritis features in both tibiofemoral and patellofemoral compartments and were scored for tibiofemoral joint-space narrowing, using the Kellgren and Lawrence scale.

Of 2,259 knees eligible for incident radiographic osteoarthritis, 215 (9.5%) developed new disease, with most (181 knees) developing disease in the tibiofemoral compartment.

However, after adjusting for age, sex, body mass index (BMI), knee-injury history, and correlation between knees, the researchers found that neither recreational walking (more miles per week), jogging, running, intensity of workouts (frequent working up a sweat), nor high activity levels relative to peers were associated with a decrease or increase in the risk of knee osteoarthritis.

Generally the risk of osteoarthritis was close to null (adjusted OR 1.10) for those who walked the most (six or more miles a week), with confidence bounds narrow enough to suggest that neither a substantial increase nor a decrease in risk was being missed, the researchers said.

When the researchers compared working up a sweat or physical activity with others the same age, the findings were similar: physical activity appeared to have little effect on the risk of knee osteoarthritis.

Comparing radiographs taken at baseline and at the end of the study, the investigators reported that joint space width was also unaffected by activity or weight and that there was no evidence that physical activity benefits cartilage.

Persons with a BMI above the median (27.7 kg/m² for men and 25.7 kg/ m² for women; mean BMI >30 kg m²/ for both) had no increase in the risk of osteoarthritis according to different types of activity.

For example, the OR of walking at least six miles a week and subsequent knee arthritis in overweight subjects was 0.95 (95% CI 0.55 - 1.620). Similar results for these subjects were found for working up a sweat three or more times a week (OR 1.04, CI 0.55-1.96).

Even though overweight persons in this cohort had an increased risk of developing osteoarthritis, physical activity did not contribute to this increase, the researchers said.

The study had many strengths, including the large number of subjects and the review of specific activities. However, limitations included the lack of MRI imaging at the baseline evaluation, and the shortage of joggers and runners to evaluate the effect of running on osteoarthritis. The results for symptomatic osteoarthritis did not suggest any effect of running, but confidence bounds were wide, the researchers said.

In conclusion, Dr. Felson wrote, walking for exercise and other recreational activities in older persons without knee osteoarthritis do not affect these individuals' risk of developing the knee disorder, even if they are overweight.

Although dynamic loading may have a trophic effect on cartilage, the investigators found no measurable protective effect of recommended weight-bearing exercise on osteoarthritis. Physical activity can be done safely without concern that a person will develop knee osteoarthritis as a consequence, the researchers concluded.

In the same journal issue, a Dutch review paper of predictive factors for knee osteoarthritis supported Dr. Felson's findings.

In an overview of 37 studies up to December 2003, researchers from the Netherlands, led by J.N. Belo, M.D., of Erasmus Medical Center in Rotterdam, found no strong evidence that regular exercise, as well as sex, knee pain, quadriceps strength, and knee injury, were associated with the progression of knee osteoarthritis.

On the other hand, Dr. Belo said, the presence of generalized osteoarthritis and the level of hyaluronic acid in the joints were predictive of disease progression.

Conflicting evidence for associations was found for several factors including body mass index and age. Limited evidence for an association with progression of knee osteoarthritis was found for several factors, including the alignment (varus/valgus) of the joint.

Limited evidence for no association with progression of osteoarthritis was also found for several factors, including meniscectomy, several markers of bone or cartilage turnover, and the clinical diagnosis of localized osteoarthritis.

Generalized osteoarthritis and level of hyaluronic acid seem to be associated with the radiologic progression of knee

osteoarthritis. Knee pain, radiologic severity at baseline, sex, quadriceps strength, knee injury, and regular sport activities seem not to be related. For other factors, the evidence was limited or conflicting, Dr. Belo concluded.

Future study of clinical progression of knee osteoarthritis is of major importance because of its implications for patient

information and appropriate medical treatment. In the case of strong evidence for either the presence or the absence of an association, future scientific consensus is needed on how to summarize the evidence provided by studies with a small sample size.

"In summary, this review provides the currently available evidence, but also identifies the lack of data with respect to prognostic factors of progression of knee osteoarthritis," Dr. Belo's team wrote.

In an accompanying editorial, Marian Minor, Ph.D., of the University of Missouri in Columbia, wrote that Dr. Felson and his colleagues have produced a useful and valid study that supports recommending regular moderate physical activity without undue fear that such activities may increase the risk of knee osteoarthritis.

A most intriguing question arising from this study concerns the other variables that might be making important contributions to the manifestation and progression of knee osteoarthritis, Dr. Minor said. "Our inability to find the answer to this question within this as well as in most other studies is not due to poor design or implementation, but results from missing data" she said.

Future research, Dr. Minor suggested, should characterize subjects in terms of variables relevant to knee osteoarthritis. These variables will likely include individual characteristics, such as age of onset, occupational and medical history, rate and site of progression, remission and repair, responses to various pharmacologic agents, physical interventions, as well as social and environmental factors.

"In addition to improving the usefulness of knee osteoarthritis research, our ultimate aim must be to produce evidence that assists clinical decision-making and individualized recommendations regarding safety and effectiveness of interventions, including physical activity," Dr. Minor concluded.