Background/Purpose: Knee osteoarthritis (OA) commonly begins as a unilateral disease, with pain in only one knee. Yet 88% of persons with unilateral knee OA develop bilateral disease within 10 years. Between-limb differences in stance time while walking may be a modifiable risk factor that plays a role in the progression from unilateral to bilateral disease. Therefore, the purpose of this study was to determine if stance time asymmetry while walking is a risk factor for incident frequent pain in the contralateral knee for older adults with unilateral frequent knee pain (FKP).

Methods: Participants with unilateral FKP (i.e., pain on most days of the past month) at the 60-month visit of the MOST study were included in this analysis. MOST is a NIH-funded cohort study of persons with or at risk for knee OA. Participants performed 4 walking trials at their usual walking speed over a 4.9 m instrumented walkway. Average stance time was calculated for each leg with all steps taken during the walking trials. A stance time limb symmetry index (LSI) was calculated as (Stance Time without FKP / Stance Time with FKP)  x100, with values >100% indicating longer stance time on the leg without FKP, values < 100% indicating longer stance time on the leg with FKP, and 100% indicating equal stance times. Incident FKP was defined by the presence of FKP at the 84-month visit for the knee without FKP at the 60-month visit. Logistic regression models determined the relation of stance time LSI to incident FKP. Covariates included age, sex, BMI, race, gait speed, previous surgery or injury to the knee without FKP, and knee pain severity of the knee without FKP. Analyses were repeated for females and males independently.

Results: 300 participants in the MOST cohort had unilateral FKP at the 60-month visit. 63% were female, 86% were white, mean (SD; min-max) age was 66.9 (8.1; 55.5-84.9) years, and BMI was 31.2 (6.8; 20.4-62.4) kg/m². For the gait evaluation, mean stance time was 708 (69; 529-986) ms on the leg with FKP and 712 (72; 514-970) ms on the leg without FKP, with a mean LSI of 100.6 (2.8; 83.9-111.3) %. Of the 300 participants, 97 (32%) developed FKP by the 84-month visit in the knee without FKP originally. Stance time LSI was significantly associated with incident FKP, with a five-unit increase in LSI (i.e., 5% longer time spent on the leg without FKP) associated with a 67% increased odds of incident FKP (OR 1.67, 95%CI 1.03-2.69, p=0.04). For females, a five-unit increase in stance time LSI was associated with a 86% increased odds in incident FKP (OR 1.86, 95%CI 1.01-3.43, p=0.048), while for males a five-unit increase was associated with a 65% increased odds in incident FKP (OR 1.65, 95%CI 0.71-3.83, p=0.24).

Conclusion: A high proportion (32%) of individuals with unilateral FKP have frequent pain in their contralateral knee at 2-year follow-up. A longer stance time on the leg without FKP compared to the leg with FKP appears to be a risk factor for developing frequent pain in the knee without FKP originally. The effect was similar for females and males independently. Future research is needed to determine how to best intervene.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/in-those-with-unilateral-frequent-knee-pain-between-limb-differences-in-stance-time-during-walking-increase-the-risk-of-frequent-pain-in-the-other-knee-the-most-study/