title: Comparison of multifidus muscle atrophy and trunk extension muscle strength: percutaneous versus open pedicle screw fixation.
abstract: METHODS
  This study was conducted by retrospective case selection and prospective observation of longitudinal changes of the multifidus muscle cross-sectional area and of trunk extension muscle strength in percutaneous and open pedicle screw fixations.
  
  
  OBJECTIVE
  To compare postoperative multifidus muscle atrophy and trunk muscle performance of percutaneous pedicle screw fixation against those of open pedicle screw fixation.
  
  
  BACKGROUND
  Recent attempts to combine percutaneous pedicle screw fixation with minimally invasive fusion techniques are based on an anecdotal presupposition that percutaneous pedicle screw fixation is superior to its open counterpart. However, the benefits of percutaneous pedicle screw fixation are currently poorly defined.
  
  
  METHODS
  Nineteen enrolled patients were divided as follows: 11 in the open pedicle screw fixation group (OPF group) and eight in the percutaneous pedicle screw fixation group (PPF group). The preoperative and postoperative cross-sectional area and T2-weighted signal intensity of multifidus muscle were measured by MRI, and trunk extension muscle strength was measured. In addition, various clinical variables were compared between two groups.
  
  
  RESULTS
  There was significant decrease in the cross-sectional area of multifidus muscle in the OPF group. In contrast, the results in the PPF group showed no statistical difference between preoperative results and that of the follow-up MRI. Although percutaneous pedicle screw fixation had positive effects on postoperative trunk muscle performance, clinical outcomes were not significantly different in areas of pain score, JOA score, and patient's opinion regarding the outcome of the surgery. However, percutaneous pedicle screw fixation caused less blood loss, and the proportion of patients who did not need postoperative oral analgesics was greater in the PPF group.
  
  
  CONCLUSIONS
  Percutaneous pedicle screw fixation caused less paraspinal muscle damage than open pediclescrew fixation and had positive effects on postoperative trunk muscle performance.
authors.affiliation: Department of Neurosurgery, Wooridul Spine Hospital, Seoul, Korea. nstopaz@yahoo.co.kr
authors.forename: Dong-Yun
authors.initials: DY
authors.lastname: Kim
authors.forename: Sang-Ho
authors.initials: SH
authors.lastname: Lee
authors.forename: Sang Ki
authors.initials: SK
authors.lastname: Chung
authors.forename: Ho-Yeon
authors.initials: HY
authors.lastname: Lee
mesh_terms: D000368:Aged; D001863:Bone Screws; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000473:pathology / Q000502:physiology; D009133:Muscular Atrophy / Q000209:etiology* / Q000473:pathology; D011183:Postoperative Complications / Q000209:etiology; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods*; D013168:Spondylolisthesis / Q000601:surgery*; D016896:Treatment Outcome