title: Quantification of Multifidus Atrophy and Fatty Infiltration Following a Minimally Invasive Microdiscectomy.
abstract: BACKGROUND
  Multifidus muscle degeneration and atrophy have been demonstrated following traditional open spine surgery. The purpose of this study was to quantify multifidus muscle atrophy and fatty infiltration following a 1-level minimally invasive (MIS) lumbar discectomy.
  
  
  METHODS
  Magnetic resonance imaging (MRI) of 24 patients who underwent a primary 1-level MIS microdiscectomy were reviewed. Demographics, operative levels, and time from surgery to imaging were assessed. Total and lean cross-sectional areas (CSA), T1-signal intensity ratio between the multifidus and psoas muscles, and lean-to-total CSA ratio were measured. Pre- and postoperative values were compared within each patient utilizing paired sample T-tests.
  
  
  RESULTS
  The mean age was 47.8±14.2 years. MRI was obtained 182.5±194.4 days following index surgery. On the ipsilateral side, total CSA decreased at the index level (-4.9%) and the lean CSA decreased at the index (-6.2%), inferior pedicle (-13.0%), and inferior disc levels (-18.6%). On the contralateral side, no significant decreases in total or lean CSA were demonstrated. T1-signal intensity ratios increased at all levels, but the differences were not statistically significant. The lean-to-total CSA ratio was decreased at the superior disc (-5.2%), inferior pedicle (-8.4%), and inferior disc levels (-17.2%) on the ipsilateral side and at the contralateral inferior disc level (-5.3%).
  
  
  CONCLUSIONS
  Primary 1-level MIS discectomy results in minimal short-term atrophy and fatty infiltration of the multifidus at the index level. Total CSA atrophy was mainly confined to the ipsilateral side at the index level. Lean CSA atrophy was observed mainly at and below the index level on the ipsilateral side. Fatty infiltration, as measured by the lean-to-total CSA ratio, ranged 1.2-17.2% on the ipsilateral and 0-5.3% on the contralateral side with greater fat content demonstrated caudally to the surgical level.
  
  
  CONCLUSIONS
  Overall, the majority of the multifidus muscle appears to be radiographically preserved following an MIS lumbar discectomy.
authors.affiliation: Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Tabaraee
authors.affiliation: Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL.
authors.forename: Junyoung
authors.initials: J
authors.lastname: Ahn
authors.affiliation: Department of Orthopaedics and Rehabilitation, Yale School of Medicine, New Haven, CT.
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Bohl
authors.affiliation: Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL.
authors.forename: Frank M
authors.initials: FM
authors.lastname: Phillips
authors.affiliation: Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL.
authors.forename: Kern
authors.initials: K
authors.lastname: Singh
keywords: MRI multifidus; Multifidus atrophy; T1 signal intensity; minimally invasive multifidus; multifidus fat infiltration; paraspinal atrophy