title: Heterotopic ossification and clinical outcome in nonconstrained cervical arthroplasty 2 years after surgery: the Norwegian Cervical Arthroplasty Trial (NORCAT).
abstract: Heterotopic ossification is a phenomenon in cervical arthroplasty. Previous reports have mainly focused on various semiconstrained devices and only a few publications have focused on ossification around devices that are nonconstrained. The purpose of this study was to assess the occurrence of heterotopic ossification around a nonconstrained cervical device and how it affects clinical outcome 2 years after surgery.
  
  
  
  Thirty-seven patients were included from a larger cohort of a randomized controlled trial (NORCAT) which compared single-level cervical arthroplasty with fusion. The occurrence of heterotopic ossification was assessed with a CT scan and two neuroradiologists determined its degree. For grading, we used the Mehren/Suchomel classification system (grade 0-4). The patients were divided by level of ossification, low grade (0-2) or high grade (3-4), and clinical outcomes were compared. Self-rated disability for neck and arm pain (Neck Disability Index), health-related quality of life (the Short Form-36 and EuroQol-5D), and pain (the Numeric Rating Scale 11) were used as clinical outcome measures.
  
  
  
  Heterotopic ossification was encountered in all patients 2 years after surgery. Complete fusion (grade 4) was found in 16 % of participants, and high-grade ossification (grade 3-4) occurred in 62 %. The remaining patients were classified as having low-grade ossification (grade 2). There were no differences in the clinical outcomes of patients with low- and high-grade ossification.
  
  
  
  High-grade heterotopic ossification and spontaneous fusion 2 years after surgery were seen in a significant number of patients. However, the degree of ossification did not influence the clinical outcome.
authors.affiliation: Department of Neurosurgery, Oslo University Hospital Rikshospitalet, Postboks 4950, Nydalen, 0424, Oslo, Norway. jsundset@ous-hf.no.|Faculty of Medicine, University of Oslo, Oslo, Norway. jsundset@ous-hf.no.
authors.forename: Jarle
authors.initials: J
authors.lastname: Sundseth
authors.affiliation: Department of Neuroradiology, Oslo University Hospital Rikshospitalet, Oslo, Norway.
authors.forename: Eva Astrid
authors.initials: EA
authors.lastname: Jacobsen
authors.affiliation: Department of Neurosurgery, Oslo University Hospital Rikshospitalet, Postboks 4950, Nydalen, 0424, Oslo, Norway.
authors.forename: Frode
authors.initials: F
authors.lastname: Kolstad
authors.affiliation: Department of Neuroradiology, Oslo University Hospital Rikshospitalet, Oslo, Norway.
authors.forename: Ruth O
authors.initials: RO
authors.lastname: Sletteberg
authors.affiliation: National Advisory Unit of Spinal Disorders, University Hospital of Trondheim (St Olavs Hospital HF), Trondheim, Norway.|Department of Neurosurgery, University Hospital of Trondheim (St Olavs Hospital HF), Trondheim, Norway.|University of Trondheim, Trondheim, Norway.
authors.forename: Oystein P
authors.initials: OP
authors.lastname: Nygaard
authors.affiliation: National Advisory Unit of Spinal Disorders and Department of Orthopaedic Surgery, Clinic of Orthopaedics and Rheumatology, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway.|Department of Neuroscience, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Lars Gunnar
authors.initials: LG
authors.lastname: Johnsen
authors.affiliation: Department of Biostatistics, Epidemiology and Health Economics, Oslo University Hospital, Oslo, Norway.
authors.forename: Are Hugo
authors.initials: AH
authors.lastname: Pripp
authors.affiliation: National Advisory Unit of Spinal Disorders, University Hospital of Trondheim (St Olavs Hospital HF), Trondheim, Norway.
authors.forename: Hege
authors.initials: H
authors.lastname: Andresen
authors.affiliation: Department of Neurosurgery, University Hospital of Trondheim (St Olavs Hospital HF), Trondheim, Norway.|University of Trondheim, Trondheim, Norway.
authors.forename: Oddrun Anita
authors.initials: OA
authors.lastname: Fredriksli
authors.affiliation: Department of Neurosurgery, Haukeland University Hospital, Bergen, Norway.
authors.forename: Erling
authors.initials: E
authors.lastname: Myrseth
authors.affiliation: Department of Neuroradiology, Oslo University Hospital Rikshospitalet, Oslo, Norway.|Department of Neurology and FORMI, Oslo University Hospital Ullevaal, Oslo, Norway.
authors.forename: John A
authors.initials: JA
authors.lastname: Zwart
mesh_terms: D000328:Adult; D001178:Arthroplasty / Q000009:adverse effects* / Q000379:methods; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000209:etiology / Q000601:surgery; D009999:Ossification, Heterotopic / Q000000981:diagnostic imaging / Q000209:etiology* / Q000601:surgery; D019736:Prostheses and Implants / Q000009:adverse effects*; D011474:Prosthesis Design; D011788:Quality of Life; D011843:Radiculopathy / Q000150:complications / Q000601:surgery; D012720:Severity of Illness Index; D016037:Single-Blind Method; D013123:Spinal Fusion / Q000009:adverse effects / Q000379:methods; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
keywords: Arthroplasty; Cervical; Fusion; Heterotopic ossification; Outcome