We hear a lot about various comorbidities associated with knee osteoarthritis (OA), and how addressing those additional conditions can help improve knee pain and function. But a growing body of research suggests one set of comorbidities that knee OA experts may be overlooking are those involving the foot and ankle.
In 2015, Australian researchers reported that one-fourth of patients with symptomatic tibiofemoral knee OA also had concurrent foot pain, with more than half of that group experiencing pain in both feet. And patients with foot pain, particularly bilaterally or ipsilateral to their knee pain, had worse health and function scores than those without foot pain.
More recently, the same researchers found that in asymptomatic patients at risk for knee OA, those with foot or ankle pain were significantly more likely than those without foot and ankle issues to develop symptomatic and radiographic knee OA within four years (see “Foot and ankle issues may boost risk of clinical and radiographic knee OA”).
Meanwhile, researchers from the UK reported in December that patients who have foot pain prior to undergoing knee arthroplasty have worse knee outcomes one year after surgery than those without preoperative foot pain.
At the moment, the exact nature of the relationship between foot and ankle pain and knee OA is unclear. It’s possible the association indicates a systemic manifestation of OA within a certain subgroup of patients, who might also have evidence of OA in the hip, hand, or wrist.
But there are other possibilities of greater interest to lower extremity clinicians. Inappropriate footwear can be associated with foot and ankle pain in addition to increased knee adduction moments, which may influence knee OA progression (see “Footwear and the risk of knee OA: The search for meaning in moments,” June 2015). Independent of their footwear preferences, patients with foot or ankle pain may develop biomechanical compensations that increase loading on the knee, which could lead to knee OA. And interventions designed to address chronic foot or ankle pain could inadvertently change gait in ways that also increase load on the knee.
My guess is that any of these potential explanations could be valid, at least for a subgroup of the knee OA population. But, even as we wait for researchers to further explore those issues, increased awareness of the associations between knee OA and foot and ankle pain can help lower extremity practitioners improve patient outcomes.
That starts with asking patients with knee pain whether they also have foot and ankle pain, and vice versa; they may not mention it on their own. And it means thinking about foot and ankle issues—and associated interventions—in terms of potential effects further up the kinetic chain.
Given how much we still have yet to learn about knee OA, looking at the problem from as many perspectives as possible gives each individual patient the best chance for a positive outcome. And it’s becoming increasingly clear that at least one of those perspectives should include the foot and ankle.