By Ellen Feldman, MD
Altru Health System, Grand Forks, ND
SYNOPSIS: The results of an observational study of more than 1,000 individuals age 50 years and older with knee arthritis revealed regular walking for exercise correlated with fewer reports of new knee pain and slower disease progression, as verified by radiographic evidence at eight-year follow-up.
SOURCE: Lo GH, Vinod S, Richard MJ, et al. Association between walking for exercise and symptomatic and structural progression in individuals with knee osteoarthritis: Data from the Osteoarthritis Initiative cohort. Arthritis Rheumatol 2022;74:1660-1667.
Knee osteoarthritis, distinguished by chronic pain and functional impairment, is the predominant type of arthritis in the United States. This multifactorial, progressive joint disease exhibits a global prevalence of 16%, escalating with age and obesity. Considering the significant morbidity associated with knee arthritis, research efforts are focusing on both treatment and prevention of disease progression.1
Professional bodies, such as the American College of Rheumatology and Osteoarthritis Research Society International, recommend a comprehensive approach to managing knee arthritis. This involves a multipronged approach, including behavioral, physical, and pharmacologic interventions, with a key emphasis on exercise. Walking for exercise is recommended, but there are limited studies of how walking affects knee arthritis.2 In this context, Lo et al explored the long-term effects of walking on the progression of knee arthritis.
The Osteoarthritis Initiative, currently in the 14th year of follow-up, is a longitudinal, prospective study on knee arthritis.3 Lo et al drew data from a selected group of participants in this study. Eligibility criteria included at least age 50 years at baseline evaluation and radiographic evidence of knee arthritis at baseline and at 36 or 48 months’ follow-up. Additionally, all participants in this nested study needed to complete the Historical Physical Activity Survey instrument at 96 months to retrospectively quantify level of walking for exercise. Researchers used the knee radiographs to consider the degree of osteoarthritis (using Kellgren/Lawrence [KL] scale from 0-4) and the extent of medial joint space narrowing. The Historical Physical Activity Survey instrument asks progressive questions about habitual walking for exercise from age 50 years and beyond.4
Additional data were collected regarding the presence or absence of knee replacement surgery and static alignment of the hip-knee-ankle angles, among other variables. The final data were adjusted for age, sex, and initial KL grade of severity.
Out of 1,212 respondents (mean age 63.2 ± 7.9 years), at baseline, 37% of respondents reported frequent symptoms of knee pain, 65% demonstrated some medial joint space narrowing, and 64% recorded KL scale of severity at level 2, 29% at level 3, and 7% at level 4. Results from the Historical Physical Activity Survey revealed 887 respondents reported walking for exercise since age 50 years.
The minimum estimated days of walking for exercise since age 50 years was 13, and the maximum was 2,100. The median number of days walking was 845. However, for the purposes of this study, any participant reporting walking for exercise since age 50 years was classified as a “walker,” and outcomes were analyzed for walkers vs. non-walkers without further quantification.
Respondents who self-reported walking for exercise at or after age 50 years were 40% less likely to develop new knee pain and 20% less likely to show a progression of medial joint space narrowing compared to respondents who did not endorse walking as exercise. On the other hand, there were no statistically significant differences between the two groups when studying worsening pain intensity (via KL grading) or improvement in baseline knee pain.
COMMENTARY
Lo et al contributed a study with clinically relevant findings applicable to managing patients with knee osteoarthritis, a prevalent and potentially debilitating condition that particularly affects older and/or overweight individuals. There were some limitations to generalization, but this work highlights the role of walking — an inexpensive and relatively accessible form of exercise — in the armamentarium in the fight against knee osteoarthritis. The findings suggest walking may aid in prevention of new frequent knee pain development and likely is effective in impeding the progression of the underlying disease process.
Lo et al suggested a biomechanical component to progression and management of knee osteoarthritis by stratifying the results according to static knee alignment. These results suggest walking provides greater benefit to individuals with varus or neutral alignment and is of less benefit for patients with valgus alignment. Future studies of joint alignment and benefits of specific exercises may serve to define and clarify this relationship.
The observational nature of this study limits definite conclusions related to causation. In fact, reverse causation may play a role, with individuals experiencing less pain from knee osteoarthritis more willing to walk for exercise. However, when the results were age-stratified, it did not appear walking for exercise diminished with age. Certainly, more research in this area could be helpful in making progress and informing clinical guidelines.
The authors’ reliance on self-reported and retrospective recall to determine walking for exercise presents its own pros and cons compared to more objective methods of collecting these data, such as a pedometer. The retrospective approach’s advantage lies in its capacity to gather long-term data, as pedometer use typically only covers a limited period and may not reflect habitual patterns of behavior. On the other hand, employing the Historical Physical Activity Survey instrument for recall over extended periods introduces the possibility of recall bias affecting results. With the expanding availability and better accuracy of wearable movement trackers, it is likely electronic data collection will play a role in future studies, potentially aiding in quantifying any correlation between optimal number of steps and mitigation of knee osteoarthritis disease progression.
The methodology used in this study did not include an exploration of any harm from walking. A comprehensive 2019 systematic review of the literature regarding walking and knee osteoarthritis revealed no evidence linking daily walking of fewer than 10,000 steps with accelerated disease progression, but the effects of more extended daily walking remain largely unexplored.2 Hence, employing a method to count steps accurately in future studies could hold considerable clinical implications.
For now, these findings are clinically significant for patients with knee osteoarthritis. Primary care providers can confidently recommend walking for exercise as part of managing this progressive condition, remembering that Lo et al did not explore walking in contexts other than exercise, such as for work or transportation, and that factors such as bone structure may limit the benefits of this type of exercise for the management of knee osteoarthritis.
REFERENCES
- Cui A, Li H, Wang D, et al. Global, regional prevalence, incidence and risk factors of knee osteoarthritis in population-based studies. EClinicalMedicine 2020;29-30:100587.
- Kraus VB, Sprow K, Powell KE, et al; 2018 Physical Activity Guidelines Advisory Committee. Effects of physical activity in knee and hip osteoarthritis: A systematic umbrella review. Med Sci Sports Exerc 2019;51:1324-1339.
- National Institute of Arthritis and Musculoskeletal and Skin Diseases. Osteoarthritis Initiative. Updated May 2023.
- Friedenreich CM, Courneya KS, Bryant HE. The lifetime total physical activity questionnaire: Development and reliability. Med Sci Sports Exerc 1998;30:266-274.