Immediate Effects of Therapeutic Ultrasound on Quadriceps Spinal Reflex Excitability in Patients with Knee Pathology
Norte GE., Saliba SA., Hart JM. Archives of Physical Medicine and Rehabilitation. 2015. Ahead of Print
Take Home Message: Quadriceps spinal-reflexive excitability was greater 20 minutes following non-thermal therapeutic ultrasound compared with a sham treatment among individuals with a history of knee injury and quadriceps dysfunction.
After a knee injury many patients have persistent muscle weakness, which may be influenced by arthrogenic muscle inhibition, which is a diminished ability to activate healthy peri-articular muscle tissue in the presence of joint pathology. This inhibition may be due to abnormal sensory information from joint mechanoreceptors. A therapeutic modality involving mechanical vibrations, such as low-intensity continuous ultrasound, may reduce muscle inhibition if it is able to stimulate receptors in peri-articular tissue via mechanical stimulation. Therefore, the authors conducted a randomized trial among patients with a history of knee injury and quadriceps dysfunction to compare quadriceps spinal-reflexive excitability after a single treatment of non-thermal ultrasound or a sham treatment. Thirty recreationally active participants with a self-reported history of a diagnosed knee injury and quadriceps dysfunction volunteered for this double-blinded randomized control trial. The authors measured a participant’s baseline quadriceps spinal-reflexive excitability in both legs by measuring the Hoffman’s reflex using electromyography and electrical stimulation to the femoral nerve. They also measured the peak muscle activation that could be elicited by electrical stimulation so that they could normalize the Hoffman’s reflex to the peak muscle response (H:M ratio). To confirm the baseline measurements the authors repeated them on the involved limb. After baseline testing, a blinded clinician applied ultrasound (1MHz frequency, 0.3W/cm2 intensity, 100% duty cycle; 15 participants) or a sham (0MHz, 0W/cm2; 15 participants) treatment to the involved anteromedial knee for 17 minutes. Lastly, the researchers measured the quadriceps spinal-reflexive excitability immediately following treatment as well as 20 minutes post treatment in the involved limb. Overall, participants’ knee extension strength and quadriceps spinal-reflexive excitability were both diminished in the involved leg compared to the uninvolved leg. The ultrasound group had 14-19% better quadriceps spinal-reflexive excitability 20 minutes post ultrasound application compared with the sham group. There were no differences detected during the baseline tests or immediately after treatment.
Muscular dysfunction following an injury can lead to numerous impairments detrimental to joint health. Modifying afferent signals to the central nervous system could assist in altering quadriceps dysfunction. For example, non-thermal ultrasound, which may stimulate receptors in peri-articular tissues, led to less quadriceps dysfunction 20 minutes following treatment. This supports the contribution of peripheral receptors to an arthrogenic response among patients with persistent quadriceps dysfunction. This non-invasive modality demonstrated a significant effect from a wide variety of knee injuries (anterior cruciate ligament, medial meniscus, chondromalacia), which suggests it could work among a diverse group of patients. It should be noted that the magnitude of change between non-thermal ultrasound compared to sham was low. More research is necessary to establish optimal treatment parameters, and determine clinical outcomes. In the meantime, this research demonstrates that medical personnel could use non-thermal ultrasound to stimulate reflex pathways, which could optimize therapeutic rehabilitation exercise conditions 20 minutes post treatment.
Questions for Discussion: Would you consider using nonthermal ultrasound on patients with quadriceps dysfunction? Do you think this would have a similar effect on another joint? What current modalities do you use for knee injuries? What do you usually use ultrasound to treat?
Written by: Jane McDevitt, PhD
Reviewed by: Jeff Driban
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