title: The impact of self-retaining retractors on the paraspinal muscles during posterior spinal surgery.
abstract: METHODS
  This was a prospective pilot study examining pre-, intra- and postoperative measures.
  
  
  OBJECTIVE
  The aim of the study was to investigate the effect of muscle retractors on the posterior spinal muscles during posterior spinal surgery.
  
  
  BACKGROUND
  Previous studies have identified changes in the structure and function of the back extensor mechanism as a result of low back pain. However, the effect of surgery on the functioning of these muscles, particularly surgical retraction, has received less attention.
  
  
  METHODS
  Twenty patients undergoing posterior spinal surgery were recruited into this study, and recordings of intramuscular pressure during surgery were performed using a pressure-monitoring system before insertion of retractors, 5, 30, and 60 minutes into surgery, and on removal of retractors. Before and following use of the retractors, muscle biopsies were taken from the multifidus muscle for analysis using birefringence techniques.
  
  
  RESULTS
  A significant increase in intramuscular pressure (P < 0.001) was observed during surgery. On removal of retractors, this pressure returned to or near to the original value. Analysis of muscle biopsies using calcium activated adenosine triphosphatase birefringence revealed a reduction in muscle function following prolonged use of self-retaining retractors.
  
  
  CONCLUSIONS
  A substantial rise in pressure in the erector spinae muscle during posterior spinal surgery was observed, and this appeared to be associated with marked changes in the function of the muscles. This could be an important factor in the generation of operative scar tissue and postoperative dysfunction of the spinal muscles.
authors.affiliation: Department of Musculoskeletal Surgery, Faculty of Medicine, Imperial College of Science, Technology & Medicine, Charing Cross Hospital, London, United Kingdom.
authors.forename: Heath
authors.initials: H
authors.lastname: Taylor
authors.forename: Alison H
authors.initials: AH
authors.lastname: McGregor
authors.forename: Siroos
authors.initials: S
authors.lastname: Medhi-Zadeh
authors.forename: Simon
authors.initials: S
authors.lastname: Richards
authors.forename: Nostrat
authors.initials: N
authors.lastname: Kahn
authors.forename: Jamshied Alaghband
authors.initials: JA
authors.lastname: Zadeh
authors.forename: Sean P F
authors.initials: SP
authors.lastname: Hughes
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D001706:Biopsy; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000473:pathology / Q000503:physiopathology*; D019637:Orthopedic Procedures / Q000379:methods*; D010865:Pilot Projects; D011446:Prospective Studies; D016896:Treatment Outcome