title: Effects of unilateral facet fixation and facetectomy on muscle spindle responsiveness during simulated spinal manipulation in an animal model.
abstract: OBJECTIVE
  Manual therapy practitioners commonly assess lumbar intervertebral mobility before deciding treatment regimens. Changes in mechanoreceptor activity during the manipulative thrust are theorized to be an underlying mechanism of spinal manipulation (SM) efficacy. The objective of this study was to determine if facet fixation or facetectomy at a single lumbar level alters muscle spindle activity during 5 SM thrust durations in an animal model.
  
  
  METHODS
  Spinal stiffness was determined using the slope of a force-displacement curve. Changes in the mean instantaneous frequency of spindle discharge were measured during simulated SM of the L6 vertebra in the same 20 afferents for laminectomy-only and 19 laminectomy and facet screw conditions; only 5 also had data for the laminectomy and facetectomy condition. Neural responses were compared across conditions and 5 thrust durations (≤ 250 milliseconds) using linear-mixed models.
  
  
  RESULTS
  Significant decreases in afferent activity between the laminectomy-only and laminectomy and facet screw conditions were seen during 75-millisecond (P < .001), 100-millisecond (P = .04), and 150-millisecond (P = .02) SM thrust durations. Significant increases in spindle activity between the laminectomy-only and laminectomy and facetectomy conditions were seen during the 75-millisecond (P < .001) and 100-millisecond (P < .001) thrust durations.
  
  
  CONCLUSIONS
  Intervertebral mobility at a single segmental level alters paraspinal sensory response during clinically relevant high-velocity, low-amplitude SM thrust durations (≤ 150 milliseconds). The relationship between intervertebral joint mobility and alterations of primary afferent activity during and after various manual therapy interventions may be used to help to identify patient subpopulations who respond to different types of manual therapy and better inform practitioners (eg, chiropractic and osteopathic) delivering the therapeutic intervention.
authors.affiliation: Associate Professor, Palmer Center for Chiropractic Research, Davenport, Iowa. Electronic address: william.reed@palmer.edu.
authors.forename: William R
authors.initials: WR
authors.lastname: Reed
authors.forename: Cynthia R
authors.initials: CR
authors.lastname: Long
authors.forename: Joel G
authors.initials: JG
authors.lastname: Pickar
mesh_terms: D000818:Animals; D001863:Bone Screws; D002415:Cats; D004195:Disease Models, Animal; D004558:Electric Stimulation; D007796:Laminectomy / Q000295:instrumentation / Q000379:methods*; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery; D008297:Male; D020393:Manipulation, Spinal / Q000379:methods*; D008465:Mechanoreceptors / Q000502:physiology; D009470:Muscle Spindles / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology; D011897:Random Allocation; D012016:Reference Values; D012680:Sensitivity and Specificity; D012684:Sensory Thresholds / Q000502:physiology*; D013035:Spasm / Q000503:physiopathology*; D021801:Zygapophyseal Joint / Q000601:surgery*
keywords: Chiropractic; Manipulation Spinal; Muscle Spindle; Neurons Afferent; Zygapophyseal Joint