title: The design evolution of interbody cages in anterior cervical discectomy and fusion: a systematic review.
abstract: BACKGROUND
  Anterior cervical discectomy with fusion is a common surgical procedure for patients experiencing pain and/or neurological deficits due to cervical spondylosis. Although iliac crest bone graft remains the gold standard today, the associated morbidity has inspired the search for alternatives, including allograft, synthetic and factor/cell-based grafts; and has further led to a focus on cage fusion technology. Compared to their graft counterparts, cage interbody implants have enhanced biomechanical properties, with designs constantly improving to maximise biocompatibility and osseointegration. We present a systematic review examining the historical progress of implant designs and performance, as well as an update on the currently available designs, and the potential future of cervical interbody implants.
  
  
  METHODS
  We performed a systematic review using the keywords "cervical fusion implant design", with no limits on year of publication. Databases used were PubMed, Medline, Embase and Cochrane. In addition, the search was extended to the reference lists of selected articles.
  
  
  RESULTS
  180 articles were reviewed and 64 articles were eligible for inclusion. Exclusion criteria were based around study design, implant information and patient cohorts. The evolution of cage implant design has been shaped by improved understanding of ideal anatomy, progress in materials research and continuing experimentation of structural design. Originally, designs varied primarily in their choice of structure, however long-term studies have displayed the overall advantages of non-threaded, wedge shaped cages in complementing healthy anatomical profiles, and thus focus has shifted to refining material utilisation and streamlining anterior fixation.
  
  
  CONCLUSIONS
  Evolution of design has been dramatic over the past decades; however an ideal cage design has yet to be realised. Current research is focusing on the promotion of osseointegration through bioactiviation of surface materials, as well as streamlining anterior fixation with the introduction of integrated screws and zero profile designs. Future designs will benefit from a combination of these advances in order to achieve ideal disc heights, cervical alignments and fusions.
authors.affiliation: University of New South Wales, Randwick, NSW, 2031, Australia. echong42@gmail.com.|Surgical and Orthopaedic Research Laboratory, Prince of Wales Clinical School, UNSW NSW, Randwick, 2031, Australia. echong42@gmail.com.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Chong
authors.affiliation: Surgical and Orthopaedic Research Laboratory, Prince of Wales Clinical School, UNSW NSW, Randwick, 2031, Australia. m.pelletier@unsw.edu.au.
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Pelletier
authors.affiliation: University of New South Wales, Randwick, NSW, 2031, Australia. ralphmobbs@hotmail.com.|Neurospine Clinic, Randwick, NSW, 2031, Australia. ralphmobbs@hotmail.com.|Department of Spine Surgery, Prince of Wales Hospital, Barker St, Sydney, 2031, Australia. ralphmobbs@hotmail.com.
authors.forename: Ralph J
authors.initials: RJ
authors.lastname: Mobbs
authors.affiliation: Surgical and Orthopaedic Research Laboratory, Prince of Wales Clinical School, UNSW NSW, Randwick, 2031, Australia. w.walsh@unsw.edu.au.
authors.forename: William R
authors.initials: WR
authors.lastname: Walsh
mesh_terms: D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000503:physiopathology / Q000601:surgery*; D017586:Diskectomy / Q000009:adverse effects / Q000295:instrumentation*; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology / Q000601:surgery*; D016348:Osseointegration; D011183:Postoperative Complications / Q000209:etiology; D011474:Prosthesis Design; D020127:Recovery of Function; D012307:Risk Factors; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation*; D055009:Spondylosis / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D016896:Treatment Outcome