There is a lack of knowledge about the native coronal knee alignment
in 3D. The currently used classification system (neutral, valgus and
varus) oversimplifies the coronal knee alignment. The purpose of
this study was therefore (1) to investigate the coronal knee
alignment in non-osteoarthritic knees using 3D-reconstructed CT
images and (2) to introduce a classification system for the overall
knee alignment based on phenotypes.
The hospital registry was searched for patients younger than
45 years and older than 16, who received a CT according to the
Imperial Knee Protocol. Patients with prosthesis, osteoarthritis,
fractures or injury of the collateral ligaments were excluded.
Finally, 308 non-osteoarthritic knees of 160 patients remained (102
males and 58 females, mean age ± standard
deviation (SD) 30 ± 7 years). The overall
lower limb alignment was defined as the hip-knee-ankle angle (HKA),
which is formed by lines connecting the centers of the femoral head,
the knee and the talus. The angle was measured using a commercially
planning software (KneePLAN 3D, Symbios, Yverdon les Bains,
Switzerland). Descriptive statistics, such as means, ranges, and
measures of variance (e.g., standard deviations) are presented.
Based on these results, the currently used classification system was
evaluated and a new system, based on phenotypes, was introduced.
These phenotypes consist of a phenotype-specific mean value (a HKA
value) and cover a range of ± 1.5° from
this mean (e.g., 183° ± 1.5°). The mean
values represent 3° increments of the angle starting from the
overall mean value (mean HKA = 180°; 3°
increments = 183° and 177°, 186° and
174°). The distribution of these limb phenotypes was
The overall mean HKA was 179.7° ± 2.9°
varus and values ranged from 172.6° varus to 187.1° valgus.
The mean HKA values for male and female were
179.2° ± 2.8° and
180.5° ± 2.8°, respectively, which
implied a significant gender difference (r = 0.23).
The most common limb phenotype in males was NEU0° (36.4%),
followed by VAR3° (29.2%) and VAL3° (23.1%). The most common
limb phenotype in females was NEU0° (36.4%), followed by
VAL3° (22.1%) and VAR3° (15.0%).
LEVEL OF EVIDENCE
The measurements using 3D-reconstructed CT images confirmed the
great variability of the overall lower limb alignment in
non-osteoarthritic knees. However, the currently used classification
system (neutral, varus, valgus) oversimplifies the coronal alignment
and therefore the introduced classification system, based on limb
phenotypes, should be used. This will help to better understand
individual coronal knee alignment.
Level III, retrospective cohort study.