Functional Electrostimulation Therapy for Vastus Medialis Decreases Varus Thrust During Gait

Abstract Background Varus thrust is known to affect the onset and progression of knee osteoarthritis, and delayed activation of the vastus medialis (VM) muscle has been suggested as a cause of this condition. However, no current reports exist on the effects of physical therapy on delayed activity in the VM. In this study, we investigated whether modifying VM activity delay suppresses varus thrust. Methods Ten participants (Kellgren-Laurence grades I:2, II:6, and III:2) diagnosed with knee osteoarthritis were enrolled. All patients wore a functional electrical stimulation (FES) set to contract the VM before heel contact and practiced walking for 10 min. We evaluated the patients’ varus thrust, maximal knee extension angle, maximal varus moment, and VM onset time before and after intervention. A Vicon Nexus ground reaction force meter and a wireless electromyograph DELSYS were used for the evaluation. The task involved free walking with no specified walking speed on a 10-m walkway, and measurements were taken before and after the intervention. Results Analysis revealed a significant difference in varus thrust before and after intervention (2.7 ± 1.1° vs 2.2 ± 1.3°, p < 0.05). Furthermore the vastus medialis activation time decreased following intervention (-0.06 ± 0.09 vs -0.21 ± 0.1, p < 0.05), as did the knee joint extension angle (8.7 ± 5.1° vs 5.5 ± 5.9°, p < 0.05). Similarly, the knee joint varus moment significantly increased after intervention (0.50 ± 0.20° vs 0.56 ± 0.18°, p < 0.05). Conclusion The vastus medialis muscle stabilizes the knee joint by extending the knee joint and pulling the patella inward. When the knee joint is in a slightly flexed position, the medial and lateral collateral ligaments relax, causing the knee joint to move inward and outward. The results of this study suggest that wearing FES caused the VM to act earlier in response to a heel strike, which improved the knee joint extension angle and suppressed the varus thrust.