title: A Comparison of Different Minimally Invasive and Open Posterior Spinal Procedures Using Volumetric Measurements of the Surgical Exposures.
abstract: METHODS
  A Prospective observational study.
  
  
  BACKGROUND
  Minimally invasive (MI) spine surgery techniques strive to minimize the damage to paraspinal soft tissues. Previous studies used only the length of the surgical incision to quantify the invasiveness of certain MI procedures. However, this method does not take into account the volume of muscle tissue that is dissected and retracted from the spine to achieve sufficient exposure. To date, no simple method has been reported to measure the volume of the surgical exposure and to quantify the degree of surgery invasiveness.
  
  
  OBJECTIVE
  To obtain and compare volumetric measures of various MI and open posterior-approached spinal surgical exposures.
  
  
  METHODS
  The length, the depth, and the volume of the surgical exposure were obtained from 57 patients who underwent either open or MI posterior lumbar surgery. MI procedures included the following: tubular discectomy, laminotomy, and transforaminal interbody fusion. Open procedures included the following: discectomy, laminectomy, transforaminal interbody fusion, or posterior-lateral instrumented fusion. Four attending spine surgeons at our unit performed the surgeries. To reduce variability, only single-level procedures performed between L4 and S1 vertebrae were used. The volume of exposure was obtained by measuring the amount of saline needed to fill the surgical wound completely once the surgical retractors were deployed and opened.
  
  
  RESULTS
  The average volumes in mililiters of exposure for a single-level MI procedure ranged from 9.8±2.8 to 75±11.7 mL and were significantly smaller than the average volumes of exposure for a single level open procedures that ranged from 44± 21 to 277±47.9 P<0.001. The average skin-incision lengths for single-level MI procedures ranged from 1.7±0.2 to 7.7±1.6 cm and were significantly smaller than the average skin-incision lengths for open procedures [5.2±1.4 (Table 3) to 11.3±2 cm, P<0.001]. The measured surgical depths were similar in MI and open groups (P=0.138). MI decompression and posterior fusion procedures yielded 92% and 73% reductions in the volumes of exposure, respectively. However, absolute differences in exposure volumes were larger for fusion (202 mL) compared with decompression alone (110.7 mL).
  
  
  CONCLUSIONS
  Direct volumetric measurement of the surgical exposure is obtained easily by measuring the amount of saline needed to fill the exposed cavity. Using this method, the needed surgical exposure of different spinal procedures can be quantified and compared. This volumetric measurement combined with the measure of retraction force, the duration of retraction, and the impact on soft tissue vascularity can help build a model that assesses the relative invasiveness of different spinal procedures.
authors.affiliation: Departments of *Neurosurgery †Center for Minimally Invasive Spine Surgery, Spine Institute of San Diego, San Diego, CA ‡Orthopaedic Surgery, Tel-Aviv Sourasky Medical Center, Israel.
authors.forename: Gilad J
authors.initials: GJ
authors.lastname: Regev
authors.forename: Choll W
authors.initials: CW
authors.lastname: Kim
authors.forename: Khalil
authors.initials: K
authors.lastname: Salame
authors.forename: Eyal
authors.initials: E
authors.lastname: Behrbalk
authors.forename: Ory
authors.initials: O
authors.lastname: Keynan
authors.forename: Ran
authors.initials: R
authors.lastname: Lador
authors.forename: Laurence
authors.initials: L
authors.lastname: Mangel
authors.forename: Zvi
authors.initials: Z
authors.lastname: Lidar
mesh_terms: D000368:Aged; D003710:Demography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019060:Minimally Invasive Surgical Procedures / Q000379:methods*; D012867:Skin; D013131:Spine / Q000601:surgery*