title: C1 lateral mass fixation: a comparison of constructs.
abstract: OBJECTIVE
  We review our experience and technique for C1 lateral mass screw fixation. We compare the results of 3 different constructs incorporating C1 lateral mass screws: occipitocervical (OC) constructs, C1-C2 constructs, and C1 to mid/low cervical constructs.
  
  
  METHODS
  We performed a retrospective chart review of 42 consecutive patients who underwent C1 lateral mass fixation by 2 of the authors (PVM and DC). The patient population consisted of 24 men and 18 women with a mean age of 64 years. Twenty-two patients had C1-C2 constructs. Twelve patients had constructs that started at C1 and extended to the mid/low cervical spine (one extended to T1). Eight patients underwent OC fusions incorporating C1 screws (2 of which were OC-thoracic constructs). All constructs were combined either with a C2 pars screw (38 patients), C2 translaminar screw (1 patient), or C3 lateral mass screw (3 patients). No C2 pedicle screws were used. Fusion was assessed using flexion-extension x-rays in all patients and computed tomographic scans in selected cases. Clinical outcomes were assessed with preoperative and postoperative visual analog scale neck pain scores and Nurick grading. The nuances of the surgical technique are reviewed, and a surgical video is included.
  
  
  RESULTS
  Two patients (5%) were lost to follow-up. The mean follow-up for the remaining patients was 2 years. During the follow-up period, there were 4 deaths (none of which were related to the surgery). For patients with follow-up, the visual analog scale neck pain score improved a mean of 3 points after surgery (P < .001). For patients with myelopathy, the Nurick score improved by a mean of 1 grade after surgery (P < .001). The postoperative complication rate was 12%. The complication rate was 38% in OC constructs, 17% in C1 to mid/low cervical constructs, and 0% for C1-C2 construct cases. Patients with OC constructs had the statistically highest rate of complications (P < .001). Patients with C1 to mid/low cervical constructs had more complications than those with C1-C2 constructs (P < .001). Of the 42 cases, there were 3 pseudoarthroses (1 in an OC case, 1 in a C1 to midcervical construct, and 1 in a C1-C2 construct). OC constructs had the highest risk of pseudoarthrosis (13%) (P < .001).
  
  
  CONCLUSIONS
  Patients treated with C1 lateral mass fixation constructs have a high fusion rate, reduced neck pain, and improved neurologic function. Constructs using C1 lateral mass screws do not need to incorporate C2 pedicle screws. Constructs incorporating C1 lateral mass screws are effective when combined with C2 pars screws, C2 translaminar screws, and C3 lateral mass screws. Constructs using C1 screws are associated with a higher complication rate and a higher pseudoarthrosis rate if extended cranially to the occiput or if extended caudally below C2.
authors.affiliation: Department of Neurological Surgery, University of California, San Francisco, San Francisco, California 94143-0112, USA. mummanenip@neurosurg.ucsf.edu
authors.forename: Praveen V
authors.initials: PV
authors.lastname: Mummaneni
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Lu
authors.forename: Sanjay S
authors.initials: SS
authors.lastname: Dhall
authors.forename: Valli P
authors.initials: VP
authors.lastname: Mummaneni
authors.forename: Dean
authors.initials: D
authors.lastname: Chou
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001268:Atlanto-Axial Joint / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery*; D001861:Bone Regeneration / Q000502:physiology; D001863:Bone Screws / Q000592:standards*; D001270:Cervical Atlas / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery*; D005260:Female; D006801:Humans; D016268:Internal Fixators / Q000592:standards*; D007593:Joint Instability / Q000473:pathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000209:etiology / Q000517:prevention & control / Q000601:surgery; D009777:Occipital Bone / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery*; D011183:Postoperative Complications / Q000209:etiology / Q000517:prevention & control; D011542:Pseudarthrosis / Q000209:etiology / Q000517:prevention & control; D012189:Retrospective Studies; D013122:Spinal Diseases / Q000473:pathology / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D016896:Treatment Outcome; D055815:Young Adult