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J. Bellemans, J. Oosterbosch, J. Truijen
68
Gender and
morphotype
The ongoing debate whether gender differences
in the dimensions of the knee should impact the
design of TKA components is still unsolved.
Consensus exists however on the fact that the
shape of the knee is – on average – different for
men and women [10, 11, 12, 13, 14, 15, 20].
One of the confounding observations is that
within men and women large differences exist,
with some women demonstrating a “male” type
geometry and
vice versa
, some males
demonstrating a “female” shaped anatomy. In a
recent study we explained this phenomenon by
demonstrating that not only gender, but also the
patient’s morphotype determines the shape of
the distal femur and proximal tibia, and that
this factor should therefore be taken into
account when designing gender specific TKA
implants.
In our study 1000 consecutive patients
undergoing TKA were analyzed and stratified
into three groups based upon their anatomic
constitution; endomorph, ectomorph, or
mesomorph [17, 18, 25].
Endomorphs are characterized as having a
round body shape with short and taper
extremities, mesomorphs have a muscular and
V shaped body constitution, whereas
ectomorphs have a slim and tall morphology
with long arms and legs (fig. 2).
The purpose of our study was thus to investigate
the influence of morphotype as well as gender
on the actual dimensions of the distal femur
and proximal tibia in the population undergoing
TKA [3].
Of the 250 smallest knees in our study 98%
were female, whereas 81% of the 250 largest
knees were male. In the group with intermediate
size knees, female knees were significantly
more narrow than male knees. Patients with
smaller knees (predominantly female)
demonstrated large variability between narrow
and wide mediolateral dimensions, irrespective
of gender. The same was true for larger knees
(predominantly male).
This variability within gender could partially
be explained by morphotypic variation. Patients
with short and wide morphotype (endomorph)
had, irrespective of gender, wider knees, while
patients with long and narrow morphotype
(ectomorph) had more narrow knees.
Our study therefore indicated that both
morphotype and gender are significant
determinants with respect to the geometry of
the distal femur and proximal tibia.
For the distal femoral geometry, gender was a
stronger predictor than morphotype, and
contributed 48% to the variability in distal
femoral aspect ratio, compared to 17% for
morphotype. For the proximal tibial geometry,
morphotype was the strongest predictor. The
influence was however less pronounced than
for the distal femur, with morphotype only
contributing 4% to the variability in the tibial
aspect ratio versus 2% by the patient’s gender.
In other words, although distal femoral
geometry seemed to be influenced in an
important way by gender and morphotype of
the patient, such was also true for the proximal
tibia, but to a much lesser extent [3].
The fact that morphotype is a predictive
variable to the actual shape of the knee is not so
surprising. Researchers have recognized the
close interrelationship between morphotype
and physical characteristics for a long time,
which has lead to many studies on the influence
of morphotype on physical skills and
performance [2, 8, 21, 26]. The morphotype
concept was initially introduced by Sheldon in
the 1940s, and later refined by Carter and
Heath, who defined the three basic somatotypes
(endo-, meso-, and ectomorph) based upon the
study of thousands photographed bodies of
men from front view, side view and back view
[17, 18, 25]. In this theory the three somatotypes
form a basic classification under which any
person can be subdivided depending on his
skeletal frame and body composition. Although
the morphotype concept has received many
criticism in the past for its simplicity and (mis)
use by anthropologists and behavioural
scientists to correlate certain morphotypes with
certain psychological characteristics, there is