title: Cross-sectional area of human trunk paraspinal muscles before and after posterior lumbar surgery using magnetic resonance imaging.
abstract: OBJECTIVE
  Iatrogenic injuries to paraspinal muscles during the posterior lumbar surgery (PLS) cause a reduction in their cross-sectional areas (CSAs) and contractile densities over time post-surgery. This study aims to quantify such alterations.
  
  
  METHODS
  Pre- and postoperative CSAs (~6 months interval) of all paraspinal muscles were measured in six patients undergoing PLS using a 3-T magnetic resonance (MR) scanner to quantify the alterations in geometrical and tissue effective contractile (non-fatty) CSAs of these muscles at all lumbar levels. To examine the presence of any confounding effects on recorded changes within ~7-month period, measurements were also carried out on ten healthy volunteers.
  
  
  RESULTS
  In the healthy population, an important (~22%) portion of CSA of the erector spinae (ES) was noncontractile at the lower lumbar levels. Negligible variations over time in both the total geometrical (<1.7% in average) and contractile (<1.2%) CSAs of muscles were observed in the healthy group (i.e., no confounding effect). Following PLS, significant reductions were observed in the geometrical CSA of only multifidus (MF) muscle by ~14 and 11% as well as in its contractile CSA by ~26 and 14% at the L5-S1 and L4-L5 levels, respectively.
  
  
  CONCLUSIONS
  The total CSA of ES at lower lumbar levels shows substantial noncontractile contents in both healthy and patient populations. Biomechanical models of the spine should hence account for the noncontractile contents using only the effective contractile muscle CSAs. Postoperative variations in CSAs of paraspinal muscles may have profound effects on patterns of muscle activities, spinal loading, and stability.
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, 11155-9567, Tehran, Iran.|Research Center for Biomedical Technology and Robotics (RCBTR), Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad S
authors.initials: MS
authors.lastname: Ghiasi
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, 11155-9567, Tehran, Iran. arjmand@sharif.edu.
authors.forename: Navid
authors.initials: N
authors.lastname: Arjmand
authors.affiliation: Division of Applied Mechanics, Department of Mechanical Engineering, École Polytechnique, Montréal, QC, Canada.
authors.forename: Aboulfazl
authors.initials: A
authors.lastname: Shirazi-Adl
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, 11155-9567, Tehran, Iran.|Research Center for Biomedical Technology and Robotics (RCBTR), Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Farzam
authors.initials: F
authors.lastname: Farahmand
authors.affiliation: Advanced Diagnostic and Interventional Radiology Research Center (ADIR), Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Hassan
authors.initials: H
authors.lastname: Hashemi
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, 11155-9567, Tehran, Iran.
authors.forename: Sahar
authors.initials: S
authors.lastname: Bagheri
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, 11155-9567, Tehran, Iran.
authors.forename: Mahsa
authors.initials: M
authors.lastname: Valizadeh
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000150:complications / Q000601:surgery*; D007796:Laminectomy; D017116:Low Back Pain / Q000209:etiology; D008159:Lumbar Vertebrae / Q000601:surgery*; D008161:Lumbosacral Region / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D064170:Paraspinal Muscles / Q000473:pathology* / Q000503:physiopathology
keywords: Contractile; Cross-sectional area; Magnetic resonance; Muscle atrophy; Posterior lumbar surgery