title: A biomechanical study to evaluate the effect of PMMA augmentation and restoration of the strength of cervical vertebral screws inserted in an osteoporotic vertebral body.
abstract: METHODS
  An experimental study.
  
  
  OBJECTIVE
  To compare the peak pull-out force (PPF) of vertebral screws fixed in osteoporotic vertebrae versus polymethylmethacrylate (PMMA) used for augmentation or restoration, before and after fatigue.
  
  
  BACKGROUND
  Failure of screw fixation in anterior cervical interbody fusion remains a significant clinical problem. However, little is known of the biomechanical characteristics of cervical vertebral screws before and after restoration or augmentation, especially after fatigue.
  
  
  METHODS
  Fifty fresh cervical vertebrae, of which 40 were randomly selected, from 12 adult cadavers were used. The vertebrae were divided into healthy controls, osteoporotic controls, a PMMA restoration group, and a PMMA augmentation group. In each of the control groups, 2 pilot holes on each side of 20 vertebral bodies were implanted with vertebral screws (4 mm in diameter). Each side randomly received either acute PPF or PPF beyond fatigue that was ensured using cyclic loading (2 Hz; 20,000 times). In the PMMA groups, pilot holes were drilled parallel to the sagittal plane and injected with 0.6-1.0 mL PMMA before the vertebral screw was inserted. Each side of each vertebral body randomly received either PPF or PPF beyond fatigue that was ensured using cyclic loading (2 Hz; 20,000 times). A Bose3510-AT fatigue testing machine measured the PPF of vertebral screws with or without PMMA for all specimens before and after fatigue.
  
  
  RESULTS
  In all groups, the prefatigue PPF was significantly higher than the postfatigue PPF. Compared with the prefatigue PPF, postfatigue PPF was reduced by 37.40%, 43.10%, 32.08%, and 31.85% in the healthy controls, osteoporotic controls, PMMA restoration, and PMMA augmentation groups, respectively. The acute and postfatigue PPFs of the healthy controls were significantly higher from that of the osteoporotic controls. The acute and postfatigue PPFs of both control groups were significantly lower from that of both PMMA groups. There was no difference in acute and postfatigue PPFs between the PMMA restoration and augmentation groups.
  
  
  CONCLUSIONS
  The results indicated that both PMMA augmentation and PMMA restoration could significantly increase cervical screw pull-out strength and antifatigue capability. The results provide a biomechanical justification for spine surgeons to use PMMA for augmentation or restoration in cases of surgeries with poor bone quality or osteoporotic vertebral bodies.
authors.affiliation: *Department of Anatomy, Southern Medical University, Guangdong Provincial Key Laboratory for Medical Biomechanics, Guangzhou, Guangdong, China †Department of Orthopaedics, Wenzhou Hospital of Integrated Traditional and Western Medicine, Wenzhou, Zhejiang, P.R. China.
authors.forename: Chun
authors.initials: C
authors.lastname: Chen
authors.forename: Weidong
authors.initials: W
authors.lastname: Zhao
authors.forename: Dongxu
authors.initials: D
authors.lastname: Liu
authors.forename: Peidong
authors.initials: P
authors.lastname: Sun
authors.forename: Changfu
authors.initials: C
authors.lastname: Wu
authors.forename: Jun
authors.initials: J
authors.lastname: Ouyang
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000187:drug effects; D015519:Bone Density / Q000187:drug effects; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000503:physiopathology*; D005260:Female; D005471:Fluoroscopy; D006801:Humans; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019904:Polymethyl Methacrylate / Q000494:pharmacology*
chemical_list: D019904:Polymethyl Methacrylate