The effects of aquatic therapy combined with transcranial direct current stimulation (tDCS) on proprioception and gait speed in older adults with knee osteoarthritis: an eight-week randomized sham-controlled trial.

Background: Knee osteoarthritis (KOA) is a prevalent condition among older adults, leading to impaired proprioception and reduced gait speed, which compromise mobility and quality of life. While aquatic therapy and transcranial direct current stimulation (tDCS) have individually shown potential for enhancing motor and sensory functions, their combined effects are not well understood.

Objective: This study aimed to evaluate the combined effects of aquatic therapy and tDCS on knee proprioception and gait speed in older women with KOA.

Methods: A randomized, triple-blind, parallel-group, sham-controlled clinical trial was conducted with 68 elderly women with KOA (aged 63-68 years). Participants were allocated into four groups: (1) Aquatic Therapy + Sham tDCS (2), Aquatic Therapy + Real tDCS (3), Real tDCS, and (4) Sham tDCS. Interventions were conducted twice weekly over an 8-week period. Knee proprioception was assessed using a digital goniometer, and gait speed was measured via the 10-Meter Walk Test under normal and dual-task conditions. Data were analyzed using analysis of covariance (ANCOVA), controlling for height and baseline scores.

Results: Paired t-tests revealed significant improvements in gait speed (under both normal and dual-task conditions) and knee proprioception in all intervention groups, except the Sham tDCS group (p ≤ 0.05). Analysis of covariance (ANCOVA), controlling for height and pre-test scores, showed significant between-group differences in both gait speed and knee proprioception. Post hoc comparisons indicated that the Aquatic Therapy + Real tDCS group exhibited significantly greater improvements in knee proprioception compared to both the Aquatic Therapy + Sham tDCS and Real tDCS groups (p ≤ 0.05), supporting the additive effect of real tDCS on sensory outcomes. However, no significant differences in gait speed were observed between the Aquatic Therapy + Real tDCS and Aquatic Therapy + Sham tDCS groups under either normal or dual-task conditions.

Conclusion: The combined use of aquatic therapy and tDCS appears to enhance proprioceptive function more effectively than either intervention alone, while improvements in gait speed seem primarily driven by aquatic therapy. These findings suggest that tDCS may offer sensory-specific benefits in multimodal rehabilitation for older adults with KOA. Further research is warranted to assess the long-term effects, evaluate outcomes under varied task demands, and examine the generalizability to broader populations.

Trial registration: This clinical trial was registered with Iran's Clinical Trial Registration Center (IRCT)[IRCT20190908044722N8] on 8 January 2025.