title: C1 posterior arch screw as an auxiliary anchor in posterior reconstruction for atlantoaxial dislocation associated with type II odontoid fracture: a case report and review of the literature.
abstract: BACKGROUND
  Although pedicle or lateral mass screws are usually chosen to fix atlantoaxial (C1-C2) instability, there is an increased risk for vertebral artery (VA) injury when used in patients with bone or arterial anomalies or osteoporotic bone. Here we report the C1 posterior arch screw as a new technique for upper cervical fixation.
  
  
  METHODS
  A 90-year-old man complained of upper cervical pain after falling in his house. The initial computed tomography (CT) scan showed C1-C2 posterior dislocation with a type II odontoid fracture. The patient underwent C2 fracture reduction and posterior C1-C2 fixation. On the right side of C1, because lateral mass screw placement could cause injury to the dominant VA considering a risk in oldest-old osteoporotic patients, a posterior arch screw was chosen instead as an auxiliary anchor. An intralaminar screw was placed on the right side of C2 because a high-riding VA was observed. A lateral mass screw and a pars interarticularis screw were placed on the left side of C1 and C2, respectively. Ten months later, the odontoid fracture had healed, with normal anatomical alignment. Although the patient experienced slight weakness when spreading his bilateral fingers, his overall condition was good.
  
  
  RESULTS
  We have presented a novel technique using C1 posterior arch screws for the fixation of a C1-C2 dislocation. Such a screw is an alternative to the C1 lateral mass screw in patients who are at risk for a VA injury because of anomalous bone and arterial structures or poor bone quality.
  
  
  CONCLUSIONS
  Although there have been few comparable studies, and the long-term outcome is unknown, fixation with a posterior arch screw could be a beneficial choice for surgeries involving the upper cervical region.
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan ; Department of Orthopedic Surgery, Keio University School of Medicine, 35 Shinanomachi, Tokyo, 160-8582 Shinjuku-ku Japan.
authors.forename: Narihito
authors.initials: N
authors.lastname: Nagoshi
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan.
authors.forename: Kota
authors.initials: K
authors.lastname: Suda
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan.
authors.forename: Tomonori
authors.initials: T
authors.lastname: Morita
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan.
authors.forename: Satoko
authors.initials: S
authors.lastname: Matsumoto
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Iimoto
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan.
authors.forename: Keigo
authors.initials: K
authors.lastname: Yasui
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Komatsu
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Department of Orthopedic Surgery, Spinal Cord Injury Center, Hokkaido Chuo Rosai Hospital, 3-1, Higashi-yonjo Minami-icchome, Bibai, 072-0015 Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Minami
authors.affiliation: Department of Orthopedic Surgery, Keio University School of Medicine, 35 Shinanomachi, Tokyo, 160-8582 Shinjuku-ku Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
authors.affiliation: Department of Orthopedic Surgery, Keio University School of Medicine, 35 Shinanomachi, Tokyo, 160-8582 Shinjuku-ku Japan.
authors.forename: Morio
authors.initials: M
authors.lastname: Matsumoto
authors.affiliation: Department of Orthopedic Surgery, Keio University School of Medicine, 35 Shinanomachi, Tokyo, 160-8582 Shinjuku-ku Japan.
authors.forename: Masaya
authors.initials: M
authors.lastname: Nakamura
keywords: Atlantoaxial dislocation; Odontoid fracture; Posterior arch screw; Vertebral artery injury