Cryotherapy and Acupuncture did not Immediately Change Quadriceps Motoneuron Pool Excitability in Induced Knee Pain

Abstract

PURPOSE: To examine the immediate effects of acupuncture and cryotherapy on vastus medialis (VM) motoneuron pool (MNP) excitability in subjects with experimentally induced anterior knee pain (AKP). We asked: (1) Will experimentally induced knee pain alter perceived pain (visual analog scale: VAS) and/or MNP excitability? and (2) Will treatments (acupuncture, cryotherapy, sham treatment, and normative- no treatment & no injection) alter perceived pain and/or MNP excitability? METHODS: A 4×4 randomised controlled laboratory study with repeated measures was used. Thirty-six, neurologically sound volunteers (age: 22.7 ± 1.79 yr, height: 1.82 ± 0.08 m, mass: 76.72 ± 10.15 kg) underwent one of four treatments. To mimic AKP, 5% of hypertonic saline (total volume of 8.5ml) was injected into the infrapatellar fat pad on the dominant leg. The VM Hoffman reflex (H-reflex) and motor response (M-response) was recorded from each subject at baseline (pre-injection), pre-tx (post 20 min injection), post-tx (post 50 min injection), and post20-tx (post 70 min injection). The maximum H-reflex and M-response and VAS were measured at each time period for data analysis. RESULTS: An injection of 5% hypertonic saline increased perceived pain (interaction: F42,448=4.58, P<0.001). We did not find any change on the MNP excitability (H:M ratio) among the four treatments (F3,31=1.68, P<0.19) or at any of the time intervals (F2,64=0.66, P<0.52). Cryotherapy significantly reduced perceived pain compared to acupuncture (P=0.0003) and sham treatment (P=0.0002). There was no difference between acupuncture and sham treatment (P=0.98). Fifteen minutes following application, cryotherapy decreased perceived pain (P=0.02) and the reduced pain level remained until the last measurement (70 min post injection, P=0.05). CONCLUSIONS: Our pain model caused AKP but did not change the VM MNP excitability. Cryotherapy reduced pain while acupuncture and sham treatment did not.