title: Influence of Hydroxyapatite Stick on Pedicle Screw Fixation in Degenerative Lumbar Spine: Biomechanical and Radiologic Study.
abstract: METHODS
  A prospective, within-patient, left-right comparative study.
  
  
  OBJECTIVE
  To evaluate the efficacy of hydroxyapatite (HA) stick augmentation method by comparing the insertional torque of the pedicle screw in osteoporotic and nonosteoporotic patients.
  
  
  BACKGROUND
  Unsatisfactory clinical outcomes after spine surgery in osteoporotic patients are related to pedicle screw loosening or pull-outs. HA, as a bone graft extender, has a possibility to enhance the fixation strength at the bone-screw interface.
  
  
  METHODS
  From November 2009 to December 2010, among patients who required bilateral pedicle screw fixation for lumbar spine surgery, 22 patients were enrolled, who recieved unilateral HA stick augmentation and completed intraoperative insertional torque measurement of each pedicle screws. On the basis of preoperative evaluation of bone mineral density, patients with osteoporosis had 2 HA sticks inserted unilaterally, and 1 stick for patients without osteoporosis. Pedicle screw loosening and pull-outs were assessed using 12-month postoperative CT scans and follow-up radiographs. Clinical evaluation was done preoperatively and at 1 year postoperatively, based on Visual Analog Scale score, Oswestry Disability Index, and Short Form-36 Health Survey.
  
  
  RESULTS
  Regardless of bone mineral density, the average torque value of all pedicle screws with HA stick insertion (HA stick inserted group) was significantly higher than that of all pedicle screws without HA insertion (control group) (P<0.0001). Same results were seen in the HA stick inserted subgroups and the control subgroups within both of the osteoporosis group (P=0.009) and the nonosteoporosis group (P=0.0004). There was no statistically significant difference of the rate of pedicle screw loosening in between the HA stick inserted group and the control group. Clinical evaluation also showed no statistically significant difference in between patients with loosening and those without.
  
  
  CONCLUSIONS
  The enhancement of initial pedicle screw fixation strength in osteoporotic patients can be achieved by HA stick augmentation.
authors.affiliation: *Department of Orthopedic Surgery, SMG-SNU Boramae Medical Center †Department of Orthopedic Surgery, College of Medicine, Seoul National University, Seoul, Korea.
authors.forename: Sung Joon
authors.initials: SJ
authors.lastname: Shin
authors.forename: Ji-Ho
authors.initials: JH
authors.lastname: Lee
authors.forename: Jae Hyup
authors.initials: JH
authors.lastname: Lee
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000187:drug effects; D016022:Case-Control Studies; D003710:Demography; D017886:Durapatite / Q000494:pharmacology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology* / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000187:drug effects / Q000601:surgery*; D008297:Male; D008365:Manometry; D008875:Middle Aged; D065289:Pedicle Screws; D011184:Postoperative Period; D011475:Prosthesis Failure; D014057:Tomography, X-Ray Computed; D019415:Torque
chemical_list: D017886:Durapatite