Immediate Effects of Therapeutic Ultrasound on Quadriceps Spinal Reflex Excitability in Patients With Knee Injury

ObjectiveTo investigate the effects of nonthermal therapeutic ultrasound on quadriceps spinal reflex excitability in patients with knee joint injury.DesignDouble-blind, randomized controlled laboratory study with a pretest posttest design.SettingUniversity laboratory.ParticipantsRecreationally active volunteers with a self-reported history of diagnosed intra-articular knee joint injury and documented quadriceps dysfunction (N=30).InterventionsA nonthermal ultrasound, or sham, treatment was applied to the anteromedial knee.Main Outcome MeasuresHoffmann reflex measurements were recorded at baseline, immediately postintervention, and 20 minutes post-intervention. The peak Hoffmann reflex amplitude was normalized by the peak motor response (H/M ratio) measured from the vastus medialis using surface electromyography as an estimate of quadriceps motorneuron pool excitability. A repeated-measures analysis of variance was used for comparisons.ResultsA significant group-by-time interaction was observed for mean (P=.016) and change (P=.044) in H/M ratio. The ultrasound group demonstrated significantly higher mean (P=.015) and change (P=.028) in H/M ratio 20 minutes postintervention than did the sham ultrasound group.ConclusionsQuadriceps motoneuron pool excitability was facilitated 20 minutes after a nonthermal therapeutic ultrasound treatment, and not a sham treatment. These data provide supporting evidence of the contribution of peripheral receptors in modulation of the arthrogenic response in patients with persistent quadriceps dysfunction. Future research in this area should attempt to identify optimal treatment parameters and translate them to clinical outcomes.