title: Polymethylmethacrylate augmentation of cannulated pedicle screws for fixation in osteoporotic spines and comparison of its clinical results and biomechanical characteristics with the needle injection method.
abstract: METHODS
  This is a retrospective study carried out to evaluate the clinical results of patients with osteoporosis and various spinal diseases treated surgically with polymethylmethacrylate (PMMA)-augmented cannulated pedicle screws, and to compare this method with the needle injection technique in terms of the clinical results and fixation strength.
  
  
  OBJECTIVE
  To report a technique using PMMA-augmented cannulated pedicle screws for fixation in osteoporotic spines and to compare its clinical results and biomechanical characteristics with the needle injection technique.
  
  
  BACKGROUND
  Many studies have shown that PMMA-augmented pedicle screws can significantly increase the stiffness and strength of the screw. Various designs of cannulated screws have been used for cement augmentation in experimental studies; however, clinical reports using these screws in osteoporotic patients are rare. A practical and reliable technique and optimal screw design have not yet been established.
  
  
  METHODS
  Forty-five patients (23 women, 22 men), mean age of 71.37 years (range, 53-94 y), with osteoporosis and various spinal diseases underwent spinal decompression and instrumentation with PMMA augmentation of cannulated pedicle screws. Preoperative and postoperative visual analog scale scores for pain and the Oswestry disability index questionnaire data were analyzed. Screw migration, which is the distance from the screw tip to the anterior cortex and the upper endplate of the vertebra, was also evaluated immediately after surgery and at the mean follow-up of 15.9 months. These clinical results were then compared with those reported for the needle injection technique. The pullout strength, insertional, and backout torque of these 2 techniques were compared using osteoporotic synthetic bone (0.12 g/cm).
  
  
  RESULTS
  A total of 255 out of 283 cannulated screws were augmented with PMMA. The mean visual analog scale pain score of these patients improved from 9.5 to 3.1 (P<0.01) and the functional Oswestry disability index score improved from 71% to 28.9% (P<0.01). Kyphotic deformity of the compression fracture group (19 patients) was improved from an average of 9.38 to 3.27 degrees after surgery, and to 5.45 degrees at the final follow-up (P<0.01). There was no significant vertical screw migration when the screws' distances were compared just after the operation and at the final follow-up (P>0.01). However, significant horizontal screw migration was found in lesions below the L2 level (P<0.01). There was no major neurovascular injury, except in 1 patient, who had persistent left thigh pain due to cement leakage at the L1 level, and the symptom was controlled with analgesics. The clinical results of both techniques were satisfactory and there were no significant differences. Although the pullout strength and screw backout torque was significantly higher in the needle injection group (234.1 vs. 187.8 N, 1119.6 vs. 836.7 N mm, respectively), the operation time was shorter and the cement leakage rate was less in the cannulated pedicle screw group than that of the needle injection group (211.4 vs. 296.3 min, 14.05% vs. 26.2%, respectively).
  
  
  CONCLUSIONS
  The technique of cannulated pedicle screws with PMMA augmentation used in this study can be an option for osteoporotic patients with various spinal diseases who require spinal instrumentation.
authors.affiliation: Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, National Yang-Ming University, Taiwan, ROC. mcchang@vghtpe.gov.tw
authors.forename: Ming-Chau
authors.initials: MC
authors.lastname: Chang
authors.forename: Hung-Chan
authors.initials: HC
authors.lastname: Kao
authors.forename: Szu-Han
authors.initials: SH
authors.lastname: Ying
authors.forename: Chien-Lin
authors.initials: CL
authors.lastname: Liu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001843:Bone Cements; D001863:Bone Screws; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000503:physiopathology / Q000601:surgery*; D019904:Polymethyl Methacrylate / Q000008:administration & dosage*; D012189:Retrospective Studies; D013122:Spinal Diseases / Q000503:physiopathology / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D019415:Torque; D016896:Treatment Outcome
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate