title: How to assess femoral and tibial component rotation after total knee arthroplasty with computed tomography: a systematic review.
abstract: OBJECTIVE
  One of the most important factors leading to revision of total knee arthroplasties (TKA) is malrotation of femoral and/or tibial component. Rotation measurements performed on radiographs are limited and less reliable compared to 2D computed tomography (CT). Nowadays, 2D-CT and 3D-CT can be distinguished in measuring rotation of the TKA components. The aim of this systematic review is to determine the most reliable CT techniques in measuring rotation of the TKA components and to investigate possible cut-off points that can be used in the clinician's decision for a possible revision of the TKA.
  
  
  METHODS
  A search of PubMed, Embase, the Cochrane Central Register of Controlled Trials and Web of Science was performed up to April 2015. Final selections of 12 articles were used in this systematic review.
  
  
  RESULTS
  3D-CT, compared to 2D-CT, is more reliable and shows a high level of intra- and interobserver reliability. Femoral component rotation is measured using the component's posterior condylar line or inner pegs in relation to the epicondylar axis. Five different techniques were used to measure tibial component rotation. The posterior border of the tibial component in relationship to the geometric centre and tibial tubercle was most frequently used.
  
  
  CONCLUSIONS
  This systematic review shows a strong preference for 3D-CT to determine the component's rotation following a TKA. The literature shows consensus on the reference points of the femoral component. In measurements of the tibial component, various techniques are used with similar results. No clear cut-off point for revision of malrotated TKA components can be stated because of limited evidence.
  
  
  METHODS
  III.
authors.affiliation: Department of Orthopaedic Surgery, OLVG, Amsterdam, The Netherlands. warddevalk@gmail.com.
authors.forename: Eduard J
authors.initials: EJ
authors.lastname: De Valk
authors.affiliation: Department of Orthopaedic Surgery, OLVG, Amsterdam, The Netherlands.
authors.forename: Julia C A
authors.initials: JC
authors.lastname: Noorduyn
authors.affiliation: Department of Orthopaedic Surgery, OLVG, Amsterdam, The Netherlands.
authors.forename: Eduard L A R
authors.initials: EL
authors.lastname: Mutsaerts
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000379:methods; D005269:Femur / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D007720:Knee Prosthesis; D011183:Postoperative Complications / Q000000981:diagnostic imaging*; D011475:Prosthesis Failure; D011859:Radiography; D015203:Reproducibility of Results; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging* / Q000601:surgery; D014057:Tomography, X-Ray Computed
keywords: CT; Component rotation; Computed tomography; Malrotation; Post-operative measurements; Total knee arthroplasty