Walk! A Long-Term Observational Investigation of Knee Osteoarthritis
By Ellen Feldman, MD
Altru Health System, Grand Forks, ND
Summary Points
- Eligible patients aged 50 years and older with documented knee osteoarthritis were selected from the larger multicenter Osteoarthritis Initiative, which included periodic monitoring and knee evaluations.
- To evaluate walking as exercise, the Historical Physical Activity Survey Instrument was administered to the 1,212 respondents in this study at 96 months.
- Results indicate that walking for exercise was associated with a 40% less chance of reporting new frequent knee pain and a 20% less likelihood of medial joint space narrowing. However, there was no association with improved frequency of knee pain from baseline in this group.
SYNOPSIS: An observational study of more than 1,000 individuals aged 50 years and older with knee arthritis revealed that regular walking for exercise correlates 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. Given the significant morbidity associated with knee arthritis, research efforts are focusing on both treatment strategies 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 multi-pronged approach, including behavioral, physical, and pharmacologic interventions, with a key emphasis on exercise. Walking for exercise is recommended, but there are limited studies investigating the effect that walking has on knee arthritis.2 In this context, Lo et al undertook a study designed to explore the long-term impact of walking on the progression of knee arthritis.
The Osteoarthritis Initiative, currently in the fourteenth 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 for the Lo et al study included being at least 50 years of age at baseline evaluation and radiographic evidence of knee arthritis at baseline and 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.
The knee radiographs looked primarily at 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 the age of 50 years and older.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.
Results
Out of 1,212 respondents (mean age 63.2 ± 7.9 years), at baseline, 37% of respondents reported frequent symptoms of knee pain, 65% had some medial joint space narrowing, and 64% had KL scale of severity at level 2, 29% had KL scale of severity at level 3, and 7% had KL scale of severity at level 4.
As noted, data for walking were collected via the Historical Physical Activity Survey instrument, which is a retrospective self-report with a goal of quantifying exercise over years. Results from this study revealed that 887 (73%) of the respondents reported walking for exercise since the age of 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.
In summary, respondents who self-reported walking for exercise at or after the age of 50 years had a 40% less likelihood of developing new knee pain and a 20% less likelihood of showing 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 looking at worsening of pain intensity (via KL grading) or improvement in baseline knee pain. (See Table 1.)
Table 1. Summary of Results for Walkers vs. Non-Walkers |
|||
| Walkers | Non-Walkers | Adjusted Odds Ratio (Walkers vs. Non-Walkers) | |
New frequent knee pain |
26% |
37% |
0.6 (95% CI, 0.4-0.8)* |
Improvement in baseline knee pain |
40% |
42% |
0.9 (95% CI, 0.7-1.3) |
Worsening of KL osteoarthritis severity grade |
18% |
21% |
0.8 (95% CI, 0.6-1.1) |
Worsening of medial joint space narrowing |
22% |
27% |
0.7 (95% CI, 0.6-1.0)* |
*P value < 0.05 CI: confidence interval; KL: Kellgren/Lawrence |
|||
Additional stratified (subgroup) analyses are detailed in Table 2.
Table 2. Subgroup Analyses of Walking’s Effect on Osteoarthritis Pain |
|
| Subgroup | Notes |
Varus static knee alignment |
The hip joint is deviated inward, creating a bow-legged appearance. Walkers with varus alignment reported less frequent new knee pain and less worsening of KL grade and medial joint space narrowing when compared to non-walkers. |
Neutral static knee alignment |
The hip joint is balanced and optimally aligned. Walkers with neutral alignment reported less frequent new knee pain and improvement from baseline knee pain, but they also showed evidence of worsening medial joint space narrowing compared to non-walkers. |
Valgus static knee alignment |
The hip joint is deviated outward, creating knock-kneed appearance. Walkers with valgus alignment reported more frequent new knee pain and had worsening of KL grading of knee pain compared to non-walkers. |
Age |
No significant difference were obtained from findings from the whole group (mixed ages) when respondents were stratified by age. |
KL: Kellgren/Lawrence |
|
Commentary
Lo et al contributed a study with clinically relevant findings applicable to the management of patients with knee osteoarthritis, a prevalent and potentially debilitating condition that particularly affects older and/or overweight individuals. This prospective study does have some limitations to generalization but 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 that walking may aid in prevention of the development of new frequent knee pain 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 point to walking being of greater benefit to individuals with varus or neutral alignment and of less benefit in patients with valgus alignment. Future studies looking specifically at 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 here, with individuals experiencing less pain from knee osteoarthritis being more willing to walk for exercise. However, when the results were age-stratified, it did not appear that walking for exercise diminished with age. Certainly, more research in this area could be helpful in making progress and informing clinical guidelines in this field.
The study’s 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 this 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 timeframe 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 impacting results. With the increasing availability and accuracy of wearable movement trackers, it is likely that electronic data collection will have a role in future studies, potentially aiding in quantifying any correlation between optimal number of steps and mitigation of knee osteoarthritis disease progression.
It is crucial to note that 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 found no evidence linking daily walking of fewer than 10,000 steps with accelerated disease progression, but the effects of more extended daily walking remains largely unexplored.2 Hence, employing a method to count steps accurately in future studies could hold considerable clinical implications.
For the present, this study’s findings have clear clinical significance for patients with knee osteoarthritis. Primary care providers can confidently recommend walking for exercise as part of managing this progressive condition, keeping in mind that the study 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. https://www.niams.nih.gov/grants-funding/funded-research/osteoarthritis-initiative
- Friedenreich CM, Courneya KS, Bryant HE. The lifetime total physical activity questionnaire: Development and reliability. Med Sci Sports Exerc 1998;30:266-274.
An observational study of more than 1,000 individuals aged 50 years and older with knee arthritis revealed that regular walking for exercise correlates with fewer reports of new knee pain and slower disease progression, as verified by radiographic evidence at eight-year follow-up.
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