title: Muscle spindle traffic in functionally unstable ankles during ligamentous stress.
abstract: BACKGROUND
  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.
  
  
  METHODS
  Case-control study.
  
  
  METHODS
  University laboratory.
  
  
  METHODS
  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).
  
  
  METHODS
  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.
  
  
  METHODS
  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.
authors.affiliation: University of Delaware, University of Delaware, Newark, DE 19716, USA. aneedle@udel.edu
authors.forename: Alan R
authors.initials: AR
authors.lastname: Needle
authors.forename: Swanik
authors.initials: S
authors.lastname: Charles B Buz
authors.forename: William B
authors.initials: WB
authors.lastname: Farquhar
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Thomas
authors.forename: William C
authors.initials: WC
authors.lastname: Rose
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Kaminski
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D000843:Ankle Joint / Q000503:physiopathology*; D016022:Case-Control Studies; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D008023:Ligaments, Articular / Q000503:physiopathology*; D008297:Male; D009470:Muscle Spindles / Q000503:physiopathology*; D013180:Sprains and Strains / Q000503:physiopathology*; D011795:Surveys and Questionnaires; D019415:Torque