Background/Purpose: Foot and ankle pain may be a risk factor for worsening knee pain in those with or at risk for knee osteoarthritis (KOA). Foot and ankle pain is associated with biomechanical alterations that shift load from the foot and ankle to the knees. Since increased knee joint loading is a well-established risk factor for KOA, foot and ankle pain may play a key role in the onset and progression of knee pain. Previous work has shown that pain anywhere in the foot or ankle increases the odds of worsening knee pain in those with KOA. However, this work did not account for widespread pain (WSP), which could partially explain the effect of foot and ankle pain on worsening knee pain. We aimed to determine if foot or ankle pain is associated with worsening knee pain while accounting for WSP.

Methods: We used data from the 144- and 168-month visits of the Multicenter Osteoarthritis (MOST) Study, a cohort study of persons with or at risk for KOA. At 144-months, participants were asked “On most days, do you have pain, aching, or stiffness in any joints?” If the participant answered “yes,” painful sites were marked on a homunculus. For the current study, our exposure was foot or ankle pain. For our outcome, worsening knee pain, we calculated the change in the Western Ontario and McMaster Universities Osteoarthritis Index – Pain (WOMAC-P) from 144- to 168-months for each knee, then defined “worsening” as an increase of ≥2 points. To determine the relation of foot or ankle pain to worsening pain of the ipsilateral and contralateral knees, we used logistic regression models with generalized estimating equations to account for bilateral data. Models were first adjusted for age, sex, BMI, race, depressive symptoms, and baseline WOMAC-P and Kellgren-Lawrence grade of the outcome knee. To account for WSP, analyses were then repeated adding the number of painful sites above the waist as a covariate. Those with knee replacement or missing data were excluded.

Results: 2201 participants were included (57% female; 81% white; mean (SD) age = 63.6 (10.1) years; mean (SD) BMI = 29.2 (5.6) kg/m²). Of the 3892 limbs, 1271 (33%) had foot or ankle pain. Knee pain worsened in 758 knees (19.5%). Compared to limbs without foot or ankle pain, limbs with foot or ankle pain had 1.61 (1.30-1.99) and 1.50 (1.22-1.85) times the odds of worsening ipsilateral and contralateral knee pain, respectively (Figure 1). When accounting for the number of painful sites above the waist, limbs with foot or ankle pain had 1.29 (1.03-1.61) and 1.18 (0.95-1.48) times the odds of worsening ipsilateral and contralateral knee pain, respectively (Figure 1). The mean (SD; Min-Max) number of painful sites above the waist was 1.68 (1.77; 0-10), and for each additional painful site the odds of worsening ipsilateral and contralateral knee pain were increased by 1.22 (1.16-1.29) and 1.23 (1.16-1.30) times, respectively.

Conclusion: Foot or ankle pain is associated with increased odds of worsening ipsilateral knee pain, even after accounting for WSP. The odds of worsening contralateral knee pain, on the other hand, seems to be affected by WSP. Clinicians may need to pay attention to foot and ankle pain as well as consider WSP to optimize outcomes for patients with KOA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/relation-of-foot-and-ankle-pain-to-worsening-knee-pain-the-most-study/