Muscle Spindle Traffic in Functionally Unstable Ankles During Ligamentous Stress

Abstract

Context: Ankle sprains are common in athletes, with functional ankle instability (FAI) developing in approximately half of cases. The relationship between laxity and FAI has been inconclusive, suggesting that instability may be caused by insufficient sensorimotor function and dynamic restraint. Research has suggested that deafferentation of peripheral mechanoreceptors potentially causes FAI; however, direct evidence confirming peripheral sensory deficits has been elusive because previous investigators relied upon subjective proprioceptive tests. Objective: To develop a method for simultaneously recording peripheral sensory traffic, joint forces, and laxity and to quantify differences between healthy ankles and those with reported instability. Design: Case-control study. Setting: University laboratory. Patients or Other Participants: A total of 29 participants (age = 20.9 ± 2.2 years, height = 173.1 ± 8.9 cm, mass = 74.5 ± 12.7 kg) stratified as having healthy (HA, n = 19) or unstable ankles (UA, n = 10). Intervention(s): Sensory traffic from muscle spindle afferents in the peroneal nerve was recorded with microneurography while anterior (AP) and inversion (IE) stress was applied to ligamentous structures using an ankle arthrometer under test and sham conditions. Main Outcome Measure(s): Laxity (millimeters or degrees) and amplitude of sensory traffic (percentage) were determined at 0, 30, 60, 90, and 125 N of AP force and at 0, 1, 2, 3, and 4 Nm of IE torque. Two-factor repeated-measures analyses of variance were used to determine differences between groups and conditions. Results: No differences in laxity were observed between groups (P > .05). Afferent traffic increased with increased force and torque in test trials (P < .001). The UA group displayed decreased afferent activity at 30 N of AP force compared with the HA group (HA: 30.2% ± 9.9%, UA: 17.1% ± 16.1%, P < .05). Conclusions: The amplitude of sensory traffic increased simultaneously with greater ankle motion and loading, providing evidence of the integrated role of capsuloligamentous and musculotendinous mechanoreceptors in maintaining joint sensation. Unstable ankles demonstrated diminished afferent traffic at low levels of force, suggesting the early detection of joint loading may be compromised.

Proprioception in musculoskeletal rehabilitation. Part 1: Basic science and principles of assessment and clinical interventions

“…However it is now known that joint proprioceptors provide input throughout a joint's entire ROM under both low and high load conditions stimulating strong discharges from the muscle spindle and are thus vital for joint stability (Sojka, Johansson et al 1989, Johansson, Lorentzon et al 1990, Needle, Charles et al 2013.…”

Postural stability and lower leg muscle activity during a diagonal single-leg landing differs in male collegiate soccer players with and without functional ankle instability

“…The delayed muscle reaction times implied that neuromuscular control was altered by the damaged mechanoreceptors due to ligamentous injury. Tissue trauma from an ankle sprain may therefore decrease the amplitude of sensory traffic 17) . Khin Myo Hla et al 33) , conversely, theorized that irritability of mechanoreceptors and/or nociceptors in a limb that had undergone an ankle sprain, increased the amplitude of sensory traffic, possibly suppressing the activity of γ motor neurons in the peroneus muscles.…”

“…Resultant tissue trauma from an ankle sprain could decrease the amplitude of sensory traffic (from capsuloligamentous and musculotendinous mechanoreceptors in the maintenance of joint sensation) at low levels of force. Unfortunately, the decrease in afferent traffic persisted in FAI individuals 16,17) . Palmieri-Smith et al 18) suggested that one of the plausible mechanisms leading to reduced peroneus muscle activity was the altered afferent traffic influencing the γ loop system.…”

The effectiveness of strain counterstrain in the treatment of patients with chronic ankle instability: A randomized clinical trial

“…38 Pietrosimone et al 39 concluded that alterations in neuromuscular function following a joint injury contribute to altered biomechanics possibly affecting long-term functional outcomes. Needle et al 40 suggest that subjective instability may be related to deficits in muscle spindle function during mechanical loading of the ankle. These studies provide support for the presence of neuromuscular dysfunction in CAI.…”