title: Classification of Chronic Back Muscle Degeneration after Spinal Surgery and Its Relationship with Low Back Pain.
abstract: METHODS
  Retrospective case series.
  
  
  OBJECTIVE
  To classify back muscle degeneration using magnetic resonance imaging (MRI) and investigate its relationship with back pain after surgery.
  
  
  BACKGROUND
  Back muscle injury and degeneration often occurs after posterior lumbar surgery, and the degeneration may be a cause of back pain. However, the relationship between back muscle degeneration and back pain remains controversial.
  
  
  METHODS
  A total of 84 patients (average age, 65.1 years; 38 men, 46 women) with lumbar spinal stenosis underwent posterior decompression surgery alone. MRI (1.5 tesla) was evaluated before and more than a year after surgery in all patients. Muscle on MRI was classified into three categories: low intensity in T1-weighted imaging, high intensity in T2-weighted imaging (type 1), high intensity in both T1- and T2-weighted images (type 2), and low intensity in both T1- and T2-weighted imaging (type 3). The prevalence of the types and their relationship with back pain (determined on a visual analog scale) were evaluated.
  
  
  RESULTS
  MRI revealed muscle degeneration in all patients after surgery (type 1, 6%; type 2, 82%; and type 3, 12%). Type 2 was significantly more frequent compared with types 1 and 3 (p<0.01). Low back pain was significantly improved after surgery (p<0.01). Low back pain was not associated with any MRI type of muscle degeneration after surgery (p>0.05).
  
  
  CONCLUSIONS
  Various pathologies of back muscle degeneration after posterior lumbar surgery were revealed. Type 2 (fatty) change was most frequent, and other patients had type 3 (scar) or type 1 (inflammation or water-like) changes. According to the Modic classification of bone marrow changes, Modic type 1 change is associated with inflammation and back pain. However, no particular type of back muscle degeneration was correlated with back pain after surgery.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Ohtori
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Sumihisa
authors.initials: S
authors.lastname: Orita
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Yamauchi
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Yawara
authors.initials: Y
authors.lastname: Eguchi
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Yasuchika
authors.initials: Y
authors.lastname: Aoki
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Nakamura
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Miyagi
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Kamoda
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Miyako
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Gou
authors.initials: G
authors.lastname: Kubota
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Inage
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sainoh
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Sato
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shiga
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Koki
authors.initials: K
authors.lastname: Abe
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Fujimoto
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Hirohito
authors.initials: H
authors.lastname: Kanamoto
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Inoue
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
keywords: Injury; Lumbar; Muscle; Pain; Surgery