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femoral ratio’s, compared to larger sized
knees. Since female knees are on average
smaller in size than male knees, one would
therefore expect females knees on average to
be wider in femoral aspect ratio’s compared to
male knees. The reason that this is not the case,
is the fact that not only gender, but also mor-
photype plays a role. Patients with a short and
wide morphotype (endomorphs) had, irrespec-
tive of gender, significantly greater mediolate-
ral versus anteroposterior ratio’s and thus
wider knees, compared to patients with long
and narrow morphotypes (ectomorphs), which
had a more narrow geometry both for the dis-
tal femur and proximal tibia.
Our study therefore indicates that both mor-
photype and gender are significant determi-
nants with respect to the geometry of the distal
femur and proximal tibia.
For the distal femoral geometry, gender was a
stronger predictor in our study than morphoty-
pe, and contributed 48% to the variability in
distal femoral aspect ratio, compared to 17%
for morphotype. For the proximal tibial geo-
metry, 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 seems to be influenced in an impor-
tant way by gender and morphotype of the
patient, such is also true for the proximal tibia,
but to a much lesser extent.
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 influen-
ce of morphotype on physical skills and per-
formance [2, 6, 18, 23]. The morphotype
concept was initially introduced by Sheldon in
the 1940s, and later refined by Carter and
Heath, who defined the three basic somato-
types (endo-, meso-, and ectomorph) based
upon the study of thousands photographed
bodies of men from front view, side view and
back view [14, 15, 22]. In this theory the three
somatotypes form a basic classification under
which any person can be subdivided depen-
ding on his skeletal frame and body composi-
tion. Although the morphotype concept has
received many criticism in the past for its sim-
plicity and (mis)use by anthropologists and
behavioural scientists to correlate certain mor-
photypes with certain psychological characte-
ristics, there is much less discussion on its
validity with respect to the study of physical
characteristics [2, 6, 18, 23]. Our work in a
certain way confirms this by demonstrating the
correlation of morphotype with the geometric
shape of knee.
Our study also confirms the influence of gen-
der on the shape of the knee, and therefore
seems to support the theoretical concept of
gender specific implant geometry, at least for
the intermediate sizes [1, 4, 5, 8, 16, 19].
Whether such implants could lead to improved
clinical results, is however another matter and
until today not proven [3, 9, 10]. In view of
this it is interesting to note that our study
demonstrates that, within gender, significant
variability exists in mediolateral versus antero-
posterior dimensions, which is explained by
the influence of morphotype.
Patients with smaller knees (predominantly
female) demonstrated large variability bet-
ween narrow and wide mediolateral dimen-
sions for any given anteroposterior size, irres-
pective of gender. The same was also true for
larger knees (predominantly male). It could
therefore make sense to consider variable
mediolateral implant dimensions to span this
divergence in patient’s morphology, even
within the same gender. Again, it remains to be
seen whether such could lead to a better clini-
cal outcome, but at least our work provides a
basis to support the theoretical rationale of
such concept.
THE INFLUENCE OF MORPHOTYPE AND GENDER ON THE SHAPE OF THE KNEE IN TKA PATIENTS
157