The coronal plane alignment of the knee classification does not correlate with the functional knee phenotype classification

Abstract

Purpose It is now well established that the coronal anatomy of the lower limb is highly variable both in non-arthritic subjects and subjects undergoing total knee arthroplasty (TKA). Two new classiications were recently described independently, but never compared: functional knee phenotypes classiication and coronal plane alignment of the knee (CPAK) classiication. The hypothesis of this study was that there was a signiicant diference between the values of the hip-knee-ankle angle (HKA) and the arithmetic hip-knee-ankle angle (aHKA) measures in the same patient at the time of TKA. Methods Five hundred and twenty cases were randomly selected among patients operated on for a TKA with navigation assistance. Anatomical parameters were collected during surgery by a navigation system, and the corresponding data of the CPAK classiication were calculated. The numerical values of measured HKA and aHKA in the same patient were compared. ResultsThe measured HKA had a mean of 3.0° varus (standard deviation of 6.0°). The calculated aHKA had a mean of 1.8° varus (standard deviation 4.8°). There was a signiicant diference between the values of the two measurements in the same subject (p = 0.005) and a weak negative correlation between the values of the two measurements in the same subject. In addition, there was no relationship between HKA values and joint line obliquity values or CPAK class. Conclusion A signiicant diference and a weak correlation between the values of the HKA and aHKA measures in the same subject were observed. The two analysis techniques used provide diferent information, and their correlation is only partial. These two techniques therefore appear to be complementary rather than exclusive. The clinical relevance of using these techniques during TKA remains unknown. Level of evidence III.

Functional knee phenotypes appear to be more suitable for the Chinese OA population compared with CPAK classification: A study based on 3D CT reconstruction models

“…The mHKA takes into account the angle between femoral and tibial mechanical axis, whereas the aHKA focuses more on the difference between femoral and tibial joint lines. Thus, functional knee phenotypes and CPAK, although both focus on coronal lower limb alignment, are two different classifications [14]. However, the deviation between aHKA and mHKA became greater along with a more VAR alignment (Figure 3).…”

“…The results of three radiographic studies [13, 19, 27] based on a total of 11,598 Caucasian OA knees and 200 Chinese OA knees showed that the FMA measurements were similar to the present study (Caucasian: 91.4° ± 2.9° [27] and 92.7° ± 2.8° [13] vs. Chinese: 91.3° ± 1.8° [19] and 91.3° ± 3.2°), but the TMA (Caucasian: 86.8° ± 3.1° [27] and 87.2° ± 3.2° [13] vs. Chinese: 85.7° ± 2.1° [19] and 84.7° ± 4.4°), the mHKA (Caucasian: 177.3° ± 7.6° [13] vs. Chinese: 172.5° ± 3.4° [19] and 172.1° ± 7.2°) and the aHKA (Caucasian: 179.9° ± 4.8° [13] vs. Chinese: 177.0° ± 2.6° [19] and 176.0° ± 6.2°) in Caucasian OA knees were more neutral [14]. Interestingly, studies noted that the Caucasian OA males had more VAR mHKA, FMA and TMA than the females [7, 13].…”

Significant difference in femoral torsion between coronal plane alignment of the knee type 1 and 4

“…A recent study compared the CPAK classification with the functional knee phenotype classification by applying both classifications to a total of 520 patients and comparing the values of the leg alignment parameters for each individual [18]. A fundamental difference between these classifications is that CPAK uses aHKA, and Hirschmann et al use mHKA to determine overall leg alignment.…”

Impact of change in coronal plane alignment of knee (CPAK) classification on outcomes of robotic-assisted TKA

“…In 2019, Hirschmann et al [ 16 ] studied coronal plane alignment of normal subjects and defined different global, femoral and tibial phenotypes. Jenny et al [ 17 ] compared CPAK classification with the functional knee phenotype classification and found significant differences and a weak correlation between HKA and aHKA in the same individuals.…”