Riann M. Palmieri

Arthrogenic Muscle Inhibition in the Leg Muscles of Subjects Exhibiting Functional Ankle Instability

Background: Functional ankle instability or a subjective report of “giving way” at the ankle may be present in up to 40% of patients after a lateral ankle sprain. Damage to mechanoreceptors within the lateral ankle ligaments after injury is hypothesized to interrupt neurologic feedback mechanisms resulting in functional ankle instability. The altered input can lead to weakness of muscles surrounding a joint, or arthrogenic muscle inhibition. Arthrogenic muscle inhibition may be the underlying cause of functional ankle instability. Establishing the involvement of arthrogenic muscle inhibition in functional ankle instability is critical to understanding the underlying mechanisms or chronic ankle instability. The purpose of this investigation was to determine if arthrogenic muscle inhibition is present in the ankle joint musculature of patients exhibiting unilateral functional ankle instability. Methods: Twenty-nine subjects, 15 with unilateral functional ankle instability and 14 healthy control subjects, consented to participate. Bilateral soleus, peroneal, and tibialis anterior H-reflex and M-wave recruitment curves were obtained. Maximal H-reflex and maximal M-wave values were identified and the H:M ratios were calculated for data analysis. Separate 1 × 2 ANOVA were done for both the functional ankle instability and control groups to evaluate differences between limbs on the H:M ratios. Bonferroni multiple comparison procedures were used for post hoc comparisons (p ≤ 0.05). Results: The soleus and peroneal H:M ratios for subjects with functional ankle instability were smaller in the injured limb when compared with the uninjured limb (p < 0.05). No limb difference was detected for the tibialis anterior H:M ratio in the functional ankle instability group (p = 0.904). No side-to-side differences were detected for the H:M ratios in patients reporting no history of ankle injury (p > 0.05). Conclusions: Depressed H:M ratios in the injured limb suggest that arthrogenic muscle inhibition is present in the ankle musculature of patients exhibiting functional ankle instability. Establishing and using therapeutic techniques to reverse arthrogenic muscle inhibition may reduce the incidence of functional ankle instability.

Pre-synaptic modulation of quadriceps arthrogenic muscle inhibition

Arthrogenic muscle inhibition (AMI) impedes rehabilitation following knee joint injury by preventing activation of the quadriceps. AMI has been attributed to neuronal reflex activity in which altered afferent input originating from the injured joint results in a diminished efferent motor drive to the quadriceps muscles. Beginning to understand the mechanisms responsible for muscle inhibition following joint injury is vital to control or eliminate this phenomenon. Therefore, the purpose of this investigation is to determine if quadriceps AMI is mediated by a presynaptic regulatory mechanism. Eight adults participated in two sessions: in one session their knee was injected with saline and in the other session it was not. The maximum Hoffmann reflex (H-reflex), M-wave, reflex activation history, plasma epinephrine, and norepinephrine were recorded at: baseline, post needle stick, post lidocaine, and 25 and 45xa0min post effusion. Measures for the control condition were matched to the effusion condition. The percent of the unconditioned reflex amplitude for reflex activation history and the maximum H-reflex were decreased at 25 and 45xa0min post effusion as compared to measures taken at baseline, post needle stick, and post lidocaine (P<0.05). No differences were noted for the maximum M-wave or plasma epinephrine and norepinephrine levels in either the effusion or noneffusion admission (P>0.05). No differences were detected at any time interval for any measure during the control admission (P>0.05). Quadriceps AMI elicited via an experimental knee joint effusion is, at least in part, mediated by a presynaptic mechanism.

Intersession reliability of a protocol to assess reflex activation history in the vastus medialis

The purpose of this study was to determine the reliability of a protocol to assess reflex activation history in the vastus medialis. Eight subjects reported to the laboratory on two occasions. Reflex activation history was assessed by delivering two stimuli of the same intensity 80 ms apart. The dependent variable evaluated was the percentage of the unconditioned reflex amplitude. Eight trials were elicited and averaged on each day. An intraclass correlation coefficient (ICC 2,1) was used to estimate intersession reliability. The ICC for the protocol was found to be 0.9647. The results of this investigation indicate that this technique can reliably estimate reflex activation history in the vastus medialis.