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abstract
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PURPOSE
The currently used system to classify the lower limb alignment
(neutral, varus, valgus) does not consider the orientation of the
joint line or its relationship to the overall lower limb alignment.
Similarly, current total knee arthroplasty (TKA) alignment concepts
do not sufficiently consider the variability of the native coronal
alignment. Therefore, the purpose of this study was (1) to introduce
a new classification system for the lower limb alignment, based on
phenotypes, and (2) to compare the alignment targets of different
TKA alignment concepts with the native alignment of
non-osteoarthritic patients.
METHODS
Two recent articles phenotyped the lower limb, the femur and tibia
of 308 non-osteoarthritic knees of 160 patients [male to female
ratio = 102:58, mean
age ± standard deviation
30 ± 7 years (16-44 years)]. The
present study introduces functional knee phenotypes, which are a
combination of all previously introduced phenotypes. The functional
knee phenotypes therefore enable an evaluation of all parameters in
relation to each other and thus a comprehensive analysis of the
coronal alignment. The existing functional knee phenotypes in the
female and male population were investigated. In addition, how many
non-osteoarthritic knees had an alignment within the range of
current TKA alignment targets (mechanical, anatomical and restricted
kinematic alignment) was investigated. Therefore, it was defined
which functional knee phenotypes represented a target of the TKA
alignment concepts and which percentage of the population had such a
phenotype.
RESULTS
Out of 125 possible functional knee phenotypes, 43 were found (35
male, 26 and 18 mutual). The most common functional knee phenotype
in males was
NEU0° + NEU0° + NEU0° (19%),
followed by
VAR3° + NEU0° + VAR0°
(8.2%). The most common functional knee phenotype in females was
NEU0° + NEU0° + NEU0°
(17.7%), closely followed by
NEU0° + NEU0° + VAL0°
(16.6%). The functional knee phenotype representing a mechanical
alignment target was found in 5.6% of the males and 3.6% of the
females. The phenotype representing an anatomical alignment target
was found in 18% of the males and 17% in females. Five of the nine
phenotypes representing a restricted kinematic alignment target were
found in this population (male 5, female 4, mutual 4). They
represented 31.3% of all males and 45.1% of all females.
CONCLUSION
A more individualized approach to TKA alignment is needed. The
functional knee phenotypes enable a simple, but detailed assessment
of a patient's individual anatomy and thereby could be a helpful
tool to individualize the approach to TKA.
LEVEL OF CLINICAL EVIDENCE
III, retrospective cohort study.
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