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. 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. 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). 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.
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. 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.Aims
Methods
The aim of this study was to investigate the
relationship between the geometry of the proximal femur and the incidence
of intra-operative fracture during uncemented total hip arthroplasty
(THA). We studied the pre-operative CT scans of 100 patients undergoing
THA with an uncemented femoral component. We measured the anteroposterior
and mediolateral dimensions at the level of division of the femoral
neck to calculate the aspect ratio of the femur. Wide variations
in the shape of the femur were observed, from round, to very narrow
elliptic. The femurs of women were narrower than those of men (p
<
0.0001) and small femurs were also narrower than large ones.
Patients with an intra-operative fracture of the calcar had smaller
and narrower femurs than those without a fracture (p <
0.05)
and the implanted Corail stems were smaller in those with a fracture
(mean size 9 The variability of the shape of the femoral neck at the level
of division contributes to the understanding of the causation of
intra-operative fractures in uncemented THA. Cite this article:
