Losing just one pound results in a four-fold reduction in knee joint load in overweight and obese patients with knee osteoarthritis (OA), according to a new study in the July issue of Arthritis & Rheumatism.¹

"The accumulated reduction in knee load for a one-pound loss in weight would be more than 4,800 pounds per one mile walked (assuming 1200 strides/mile)," concludes lead author Stephen P. Messier, PhD, exercise scientist at the JB Snow Biomechanics Laboratory of Wake Forest University in Winston-Salem, North Carolina. "For people losing 10 pounds, each knee would be subjected to 48,000 pounds less in compressive load per mile walked."

The researchers note that although there is a strong correlation between obesity and knee OA, some obese but otherwise healthy adults can reduce knee-joint torque and load on the knee joints during walking. Therefore, they suggest that thousands of steps accumulated during the course of a day would have a meaningful reduction in the risk of knee OA.

Seeking to investigate the direct relationship between weight loss and knee joint stress while walking, Dr. Messier and colleagues followed 142 overweight and obese individuals with reported disability and radiographic evidence of knee OA over an 18-month period. Patients were part of the Arthritis, Diet, and Activity Promotion Trial (ADAPT), a previous study that confirmed the efficacy of moderate weight loss achieved through a combination of diet and exercise as a treatment for knee OA.²

Study participants underwent three-dimensional gait analysis at baseline and at 6 and 18 months. Each participant wore an identical make and model of athletic shoe during testing. Gait kinetic outcome variables included peak knee-joint forces and peak internal knee-joint moments.

There was a significant direct association between follow-up body mass and peak follow-up values of compressive force, resultant force, abduction moment, and medial rotation moment, the new study found.

Calling the study "interesting," and noting that it corroborates other research, Wael K. Barsoum, MD, orthopaedic surgeon at the Cleveland Clinic Foundation in Ohio, tells CIAOMed that "the take-home message is that losing weight causes less force on the knee."

Dr. Barsoum adds that, unfortunately, weight loss is easier said than done. "The important point to keep in mind is that most patients, after knee replacement, actually gain weight, rather then losing it, and that people have a very difficult time losing weight before knee surgery because of their pain," he points out.

The ADAPT participants were randomly assigned to four groups: diet only, exercise only, diet plus exercise, and a control group called healthy lifestyle. The diet-only group attended regular sessions on changing eating habits and lowering calorie intake, with meal plans and guidelines for three dietary weight-loss phases: intensive, transition, and maintenance. The exercise only group attended 1-hour workout sessions 3 days a week, consisting of an aerobic phase, a resistance training phase, a second aerobic phase, and a cool-down phase. The diet plus exercise group participated in both programs. Members of the healthy lifestyle group were required to attend three educational classes on weight reduction and regular exercise, but were not enrolled in either of the study's programs or any specific plans.

Patients who combined modest weight loss with moderate exercise had an average 24% improvement in their ability to perform daily activities, accompanied by reduction in morning stiffness. The patients who combined exercise with diet also lost more weight-5.7% of total body weight, on average-than any other group. The diet plus exercise group also made significant improvements in mobility, as measured by a 6-minute walk distance and stair-climb time. In addition, this group reported the most dramatic relief from pain, although pain tended to improve for the majority of all the study's participants.

BMI linked to knee, but not hip, OA

In related news presented last month at the Annual European Congress of Rheumatology of the European League Against Rheumatism (EULAR),³ body mass index (BMI) was associated with the development of knee OA, but not hip OA. Moreover, BMI was not associated with progression of the disease at either site.

In the study, which culled data from the Rotterdam study that examined chronic disease in the elderly, researchers looked at radiographs of knees and hips among 1392 men and 1926 women aged 55 or older.

"In the knee, there is a clear relationship between [being] overweight and radiographic OA (ROA) and even more with clinical OA (COA), while this is hardly the case in hip OA," the researchers reported, adding that "our study shows that persons [who are] overweight suffer more from the same degree of ROA."

In a press release, researcher Max Reijman, MSc, clinical epidemiologist at the Erasmus Medical Center in Rotterdam, the Netherlands, notes that the discrepancy is most likely due to the differences in mechanical alignment of the two joints. That said, "the health message is clear: losing weight can help even if you already have OA."

Reijman and colleagues now plan to study pain reduction in elderly women with high BMI, in which one group will be asked to lose weight and the other will be given the supplement glucosamine.

References:

1. Messier SP, Gutekunst DJ, Davis C, DeVita P. Weight loss reduces knee-joint loads in overweight and obese older adults with knee osteoarthritis. Arthritis Rheum. 2005;52:2026-2032.
2. Messier SP, Loeser RF, Miller GD, et al. exercise and dietary weight loss in overweight and obese older adults with knee osteoarthritis: the arthritis, diet, and activity promotion trial. Arthritis Rheum. 2004;50:1501-1510.
3. Bierma-Zeinstra SMA, Reijman M, Lievemse AM, et al. Does overweight cause more pain in radiological hip and knee osteoarthritis? Presented at: Annual European Congress of Rheumatology of EULAR; June 8-11, 2005; Vienna, Austria. Abstract SAT0244