title: Postoperative displacement of hydroxyapatite spacers implanted during double-door laminoplasty.
abstract: OBJECTIVE
  Double-door laminoplasty using hydroxyapatite (HA) spacers has been widely performed for compressive cervical myelopathy and has provided good neurological outcome. Although HA spacers are used for preventing reclosure of the opened laminae, they are often displaced or dislocated from their original position. The authors investigated the incidence and patterns of postoperative HA spacer displacement to determine the reasons for this unfavorable event.
  
  
  METHODS
  Eighty-six patients with compressive myelopathy underwent double-door laminoplasty in which a total of 278 HA spacers were used. The displacement of HA spacers and opened laminae were assessed using postoperative lateral radiographs and CT scans.
  
  
  RESULTS
  Postoperative dorsal migration > 2 mm was found in 116 (42%) of 278 implanted HA spacers. In addition, 33 (38%) of 86 HA spacers rotated > 10 degrees and 29 (34%) of the 86 opened laminae tilted > 10 degrees. Moreover, deformation of the newly formed spinal canal was observed in 51 (59%) of 86 cases, and bone fusion between the HA spacer and spinous process was achieved in only 15 (8.7%) of 172 cases. Neurological worsening and neck pain, however, were not associated with displacement of HA spacers or deformation of the spinal canal.
  
  
  CONCLUSIONS
  In double-door laminoplasty, postoperative displacement of the HA spacer with deformation of the enlarged spinal canal occurred frequently. Hydroxyapatite spacers tend to become displaced after surgery. Placing the HA spacer at the base of the spinous process close to the dura mater may prevent postoperative displacement.
authors: Department of Orthopedics, National Hospital Organization Osaka Minami Medical Center, Kawachinagano, Osaka Japan. t-kaito@leto.eonet.ne.jp
authors: Takashi
authors: T
authors: Kaito
authors: Noboru
authors: N
authors: Hosono
authors: Takahiro
authors: T
authors: Makino
authors: Noriyoshi
authors: N
authors: Kaneko
authors: Masato
authors: M
authors: Namekata
authors: Takeshi
authors: T
authors: Fuji
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000601:surgery*; D017886:Durapatite; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D007796:Laminectomy / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000000981:diagnostic imaging / Q000517:prevention & control; D019736:Prostheses and Implants; D011475:Prosthesis Failure; D013117:Spinal Cord Compression / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed
chemical_list: D017886:Durapatite