title: Microendoscopic lateral decompression for lumbar foraminal stenosis: a biomechanical study.
abstract: METHODS
  A biomechanical study.
  
  
  OBJECTIVE
  How much of the facet joint and the pars interarticularis (PI) can be removed in microendoscopic lateral decompression (MELD) for lumbar foraminal stenosis (LFS)?
  
  
  BACKGROUND
  MELD is a surgical modality for patients with LFS. In severe degenerative cases, unilateral facet joint resection or unilateral removal of the lateral part of the PI are sometimes needed to decompress the nerve root adequately.
  
  
  METHODS
  Twelve human lumbar motion segments were tested according to the following loading protocol: axial compression, flexion, extension, lateral bending to the right and left, and axial rotation to the right and left. This loading protocol was applied to each motion segment after MELD in 2 experiments: (1) unilateral graded facetectomy was performed in stages of 25%, 50%, 75%, and 100% using 3 segments of L3/L4 and 3 segments of L5/S1; (2) unilateral removal of the lateral part of the PI was performed in stages of 25%, 50%, 75%, and 100% using 3 segments of L3/L4 and 3 segments of L5/S1. The relative stiffness of each motion segments was determined each time.
  
  
  RESULTS
  (1) Unilateral facet joint resection of >75% can lead to a significant reduction in stiffness in axial rotation at both L3/L4 and L5/S1. (2) Unilateral removal of 75% of the lateral part of the PI can lead to significant reduction in stiffness in right and left rotation at L3/L4 and in left rotation at L5/S1. (3) Unilateral removal of 100% of the lateral part of the PI can lead to a significant reduction in stiffness in right axial rotation at L5/S1.
  
  
  CONCLUSIONS
  It would seem judicious to remove no >50% of the facet joint or the lateral part of the PI in order to prevent postoperative instability when using MELD for LFS.
authors.affiliation: *Department of Orthopaedic Surgery, Emory Spine Center †Veterans Affairs Medical Center, Atlanta, GA ‡Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan §Department of Orthopaedic Surgery, Ilsan Paik Hospital Inje University, Goyang-si, Korea.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Enyo
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamada
authors.forename: Jung H
authors.initials: JH
authors.lastname: Kim
authors.forename: Munehito
authors.initials: M
authors.lastname: Yoshida
authors.forename: William C
authors.initials: WC
authors.lastname: Hutton
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D019245:Compressive Strength / Q000502:physiology; D019299:Decompression, Surgical / Q000379:methods*; D004724:Endoscopy / Q000379:methods; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery*; D008297:Male; D008866:Microsurgery / Q000379:methods*; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D012720:Severity of Illness Index; D013130:Spinal Stenosis / Q000000981:diagnostic imaging / Q000601:surgery*; D021801:Zygapophyseal Joint / Q000502:physiology / Q000601:surgery