title: Morphometric analysis of the distal femur in total knee arthroplasty and native knees.
abstract: OBJECTIVE
  Analysis of the morphology of the distal femur, and by extension of the femoral components in total knee arthroplasty (TKA), has largely been related to the aspect ratio, which represents the width of the femur. Little is known about variations in trapezoidicity (i.e. whether the femur is more rectangular or more trapezoidal). This study aimed to quantify additional morphological characteristics of the distal femur and identify anatomical features associated with higher risks of over- or under-sizing of components in TKA.
  
  
  METHODS
  We analysed the shape of 114 arthritic knees at the time of primary TKA using the pre-operative CT scans. The aspect ratio and trapezoidicity ratio were quantified, and the post-operative prosthetic overhang was calculated. We compared the morphological characteristics with those of 12 TKA models.
  
  
  RESULTS
  There was significant variation in both the aspect ratio and trapezoidicity ratio between individuals. Femoral trapezoidicity was mostly due to an inward curve of the medial cortex. Overhang was correlated with the aspect ratio (with a greater chance of overhang in narrow femurs), trapezoidicity ratio (with a greater chance in trapezoidal femurs), and the tibio-femoral angle (with a greater chance in valgus knees).
  
  
  CONCLUSIONS
  This study shows that rectangular/trapezoidal variability of the distal femur cannot be ignored. Most of the femoral components which were tested appeared to be excessively rectangular when compared with the bony contours of the distal femur. These findings suggest that the design of TKA should be more concerned with matching the trapezoidal/rectangular shape of the native femur.
  
  
  CONCLUSIONS
  The distal femur is considerably more trapezoidal than most femoral components, and therefore, care must be taken to avoid anterior prosthetic overhang in TKA
authors.affiliation: Centre Orthopédique Santy, 24 Av Paul Santy, Lyon, 69008, France.
authors.forename: M P
authors.initials: MP
authors.lastname: Bonnin
authors.affiliation: Accelerate Innovation Management, 1 rue de la Navigation, 1201 Geneva, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Saffarini
authors.affiliation: Hospices Civils de Lyon, 69424, Lyon, France.
authors.forename: N
authors.initials: N
authors.lastname: Bossard
authors.affiliation: Hospices Civils de Lyon, 69424, Lyon, France.
authors.forename: E
authors.initials: E
authors.lastname: Dantony
authors.affiliation: Ghent University, De Pintelaan, Ghent, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Victor
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D005269:Femur / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000473:pathology*; D010020:Osteonecrosis / Q000000981:diagnostic imaging / Q000473:pathology; D012189:Retrospective Studies; D012727:Sex Characteristics; D014057:Tomography, X-Ray Computed
keywords: Femoral component; Oversizing; Pain; TKA design; Total Knee Arthroplasty; femur; femur shape; morphotype