The Effects of Disinhibitory Transcutaneous Electrical Nerve Stimulation on Contralateral Quadriceps Activation in Osteoarthritic Patients

Abstract

Bilateral quadriceps activation failure has been reported following unilateral knee injuries, suggesting that muscle inhibition may be modulated by central nervous system processes. Transcutaneous electrical nerve stimulation (TENS) applied to the injured knee has been reported to disinhibit ipsilateral quadriceps of patients with tibiofemoral osteoarthritis (TFOA), yet no data exists regarding how the contralateral or uninjured quadriceps are affected. PURPOSE: To determine the effects of disinhibitory TENS and therapeutic exercise applied to the injured knee on the uninjured quadriceps central activation ratio (CAR). METHODS: Thirty-six participants with TFOA were stratified by Kellgren-Lawrence Score and baseline CAR, and randomized into 3 groups (control: 5M, 7F; 58.3 ± 11.8yrs, 28.6± 5.6 BMI,), placebo TENS (4M, 8F; 60.3 ± 12.9yrs, 29.5±9.8 BMI) and TENS groups (6 M,6F; 61 ± 10.9yrs, 28.6± 4.8 BMI). The involved leg was determined as the knee that had the most radiographic evidence of TFOA. All groups participated in 12 supervised, unilateral lower extremity exercise sessions over 4 weeks. TENS and placebo TENS groups wore the intervention on the injured leg during all exercise sessions and for at least 8 hours daily for 4 weeks. Quadriceps CAR was tested on the uninvolved quadriceps prior to the intervention and at 2 and 4 weeks following baseline. A 3x3 repeated measures ANOVA was used to detect differences in CAR and standardized effect sizes calculated to assess effect magnitude. RESULTS: No significant differences were found in CAR score between groups at baseline (TENS 86±10, placebo 84±15, control 84±12), 2 weeks (93±4, 84±13, 86±11) or 4 weeks (94±.07, 82±16, 81±17), yet strong to moderate effect sizes were found at 2 weeks (d =.92; 95% confidence interval.05, 1.73) and 4 weeks (.58; -.26, 1.37) in the TENS group. Weak effect sizes were calculated for both the placebo (0; -.8, 8: -.13; -.93,.68) and the control group (.17; -.63,.97: -.2; -1,.61) at 2 and 4 weeks, respectively. CONCLUSION: Although there were no statistically significant differences between groups in the uninvolved leg following 4 weeks of disinhibitory TENS treatment, effect sizes were strong, suggesting a clinically significant increase in uninvolved quadriceps CAR.