EFFECT OF INTRA‐ARTICULAR HYALURONIC ACID ON GAIT VARIABILITY IN OLDER ADULTS WITH KNEE OSTEOARTHRITIS

To the Editor: Knee osteoarthritis (OA) is a prevalent problem in older adults that is characterized by joint damage, pain, and stiffness and has been associated with a high risk of falls.1 The mechanisms of fall risk in knee OA are related to gait disturbances secondary to pain and dysfunction.1, 2 Gait disturbances, particularly gait variability, have been associated with future falls and mobility decline.3 The Osteoarthritis Research Society International recommends intra-articular hyaluronic acid (HA) to reduce pain and improve function in people with knee OA.4 Older adults with knee OA treated with intra-articular HA experience improvements in ground reaction forces while walking,5 quadriceps contraction,6 and balance sway,7 which suggests that this treatment will generate a more-stable gait pattern, but the effect of HA on gait variability in this population has not been studied. It was hypothesized that intra-articular HA injections would reduce gait variability in older adults with knee OA and consequently reduce their risk of falls. With local institutional review board approval, a randomized, double blind, placebo-controlled trial comparing the effect of HA injections with that of placebo (P) injections on gait variability as a marker of fall risk was conducted. Participants were community-dwelling older adults with mild to moderate knee OA diagnosed according to the American College of Rheumatology criteria. Exclusion criteria were OA in the hips, ankles, or feet; neurological disease that might affect gait (e.g., Parkinson's disease, stroke); and intra-articular injection 6 months or less before the study. Participants were randomized to receive three consecutive weekly knee injections of HA (20 mg/mL HA) or P (0.001 mg/mL HA). Changes in participants' fast gait velocity were selected as outcomes because they are more reliable than usual gait velocity changes in people with knee OA.8 Gait was assessed at baseline and 3 and 6 months after treatment using an electronic walkway (GAITRite, CIR Systems, Inc., Havertown, PA), and gait variability was quantified as the coefficient of variation (CoV) of stride time and double support time, because these variables are related to fall risk.4 Within- and between-group differences were determined using paired- and independent-samples t-tests, with P<.05 considered significant. Fifteen participants (53% female; mean age 71.9±6.8; mean body mass index (BMI) 30.5±6.2 kg/m2) received HA, and 15 (53% female; mean age 72.9±5.5; mean BMI 29.4±4.1 kg/m2) received P. Demographic and gait characteristics were not significantly different between the groups at baseline (P<.05). Six months after treatment, the HA group experienced a significant decrease in double support time variability (CoV=7.4±2.8% to 5.4±1.5%, P=.02, Figure 1A), whereas stride time variability (CoV=2.07±0.5% to 2.10±0.5%, P=.82, Figure 1B) remained relatively unchanged. Conversely, the P group experienced a nonsignificant decrease in double support time variability (CoV=6.8±3.3% to 6.1±2.8%, P=.56, Figure 1A) and a significant increase in stride time variability (CoV=2.0±0.8% to 2.6±0.8%, P=.04, Figure 1B), showing a less-stable gait pattern. Between-group differences regarding changes in gait variability were not significantly different 6 months from treatment (P=.06). Mean (standard error) changes (Δ), from baseline through 3- and 6-month follow-up for the coefficient of variation (%) for double support time (A) and stride time (B) in older adults with knee osteoarthritis receiving intra-articular hyaluronic acid (HA) and placebo (P); *paired-samples t-test P<.05. This preliminary trial demonstrates that intra-articular HA injection may conserve or improve the stability of gait in people with knee OA. Six months after treatment, the people with knee OA receiving HA had a more-stable gait pattern than those receiving P. In the HA group, stride time variability remained relatively unchanged, and double support time variability decreased significantly. In the P group, stride time variability increased significantly, and double support time did not decrease significantly. Furthermore, the differences in gait variability between the HA and P groups increased over time from treatment. This slow-onset but long-lasting effect of HA has previously been demonstrated in knee OA pain studies.9 Gait variability has been evaluated frequently in cohort studies as a marker of fall risk and mobility disability in older adults,10 but studies assessing the effect of interventions on gait variability are scarce. Knee OA is an important determinant of gait, mobility, and fall risk in older adults, and the results of the current study demonstrate less gait variability in people with knee OA after treatment. Therefore, gait variability may be an important outcome when considering mobility impairment, functionality, and safety in this population. These findings offer support for and rationale to assess the effect of intra-articular HA on gait variability and falls risk in older adults with knee OA in a larger clinical trial. We are grateful for Sheree Shapiro's assistance with the randomization process. Conflict of Interest: The authors have no financial or personal conflicts with this letter. This study was funded by the Physicians' Services Incorporated Foundation and the Canadian Institutes of Health Research. Author Contributions: Study concept and design: JD, RP, DW, BC, MMO. Acquisition of subjects and data: JD, RP, MMO. Analysis and interpretation of data: JD, RP, MMO. Preparation of manuscript: JD, MMO. Critical review of manuscript: JD, RP, DW, BC, MMO. Sponsor's Role: The funding sources had no role in the design, methodology, data analysis, or preparation of this manuscript.

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