title: Component rotational alignment in unexplained painful primary total knee arthroplasty.
abstract: BACKGROUND
  Rotational malalignment of the components in total knee arthroplasty (TKA) can be a factor in poor outcomes but has yet to be defined. This study compares the rotational alignment of components in a cohort of 56 patients with unexplained pain following total knee arthroplasty with a matched control cohort of 56 patients with cemented Nex Gen Legacy posterior stabilised (LPS) flex fixed bearing TKA between March 2006 and May 2010. The aim of the study was to define an acceptable limit of rotation in total knee replacement.
  
  
  METHODS
  Rotational alignment was calculated using the Berger protocol with post operative computerised tomography scanning. The alignment parameters measured were tibial and femoral component rotations and the combined component rotations and the component rotational mismatch.
  
  
  RESULTS
  The two cohorts were demographically matched. Excessive internal rotation of the components was defined using the tenth percentile of rotations in the control cohort. Values of excessive internal rotation were 5.8° of the tibial component, 3.9° of the femoral component, 8.7° of combined rotation and 5.6° of the component mismatch. No significant difference was identified in excessive external rotation in any of the parameters. A significant difference in the mean rotations between the two cohorts was identified with internal rotation of the components in the painful cohort and external rotation on the control cohort.
  
  
  CONCLUSIONS
  We identified internal rotation malalignment of the tibial (p=0.0003) and femoral (p=0.014) components individually as well as the combined component rotation (p=0.0003) and component rotation mismatch (p=0.0001) to be a factor in pain following TKA. External rotation of any of the component parameters was not identified to be a factor in painful TKA. This study adds to the understanding of rotational alignment in TKA and suggests limits of internal rotation alignment associated with painful Nex Gen Legacy posterior stabilised (LPS) flex fixed bearing TKA.
  
  
  METHODS
  Level III.
authors.affiliation: Glasgow Royal Infirmary. Electronic address: drstuartbell@gmail.com.
authors.forename: Stuart W
authors.initials: SW
authors.lastname: Bell
authors.affiliation: Glasgow Royal Infirmary.
authors.forename: Peter
authors.initials: P
authors.lastname: Young
authors.affiliation: Glasgow Royal Infirmary.
authors.forename: Colin
authors.initials: C
authors.lastname: Drury
authors.affiliation: Glasgow Royal Infirmary.
authors.forename: Jules
authors.initials: J
authors.lastname: Smith
authors.affiliation: Glasgow Royal Infirmary.
authors.forename: Iain
authors.initials: I
authors.lastname: Anthony
authors.affiliation: Glasgow Royal Infirmary.
authors.forename: Bryn
authors.initials: B
authors.lastname: Jones
authors.affiliation: Glasgow Royal Infirmary.
authors.forename: Mark
authors.initials: M
authors.lastname: Blyth
authors.affiliation: Glasgow Royal Infirmary.
authors.forename: Angus
authors.initials: A
authors.lastname: McLean
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery; D007720:Knee Prosthesis / Q000009:adverse effects*; D008297:Male; D010149:Postoperative Pain / Q000209:etiology*; D011475:Prosthesis Failure; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging* / Q000601:surgery; D014057:Tomography, X-Ray Computed
keywords: Rotational alignment; Total knee arthroplasty