Coronal Plane Alignment of the Knee (CPAK) Classification [1]
The CPAK classification is a method for classifying constitutional coronal lower limb alignment. Knees are classified according to joint line obliquity (JLO) and the arithmetic hip-knee-ankle alignment (aHKA). The aHKA is a method for calculating constitutional HKA alignment for an arthritic knee [2]. The only two measurements required are the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) these require long leg alignment xrays.
Kinematic alignment led to a greater proportion of optimally balanced knees across all CPAK types compared to mechanical alignment and this effect was largest for CPAK Type I, II and IV. Restricted safe zones for kinematic alignment were defined as 86° to 93° for recreation of both the LDFA and the MPTA, and -5° varus to +4° valgus for the final mHKA. While kinematic alignment improves knee balance it remains to be seen if this leads to improvements in PROMs and implant survivorship. The excel calculator above enables the plotting of knee phenotype on the CPAK matrix. There is an additional feature that allows surgical planning of bony cuts using an instrumented knee replacement system and plots the effect this will have upon post-operative CPAK.
This is a fantastic piece of work conducted by Macdessi and his co-authors. I had no involvement in this but wanted to share this calculator to help you classify knees.
1. MacDessi SJ, Griffiths-Jones W, Harris IA, et al (2021) Coronal Plane Alignment of the Knee (CPAK) classification. Bone Joint J 103-B:329–337. https://doi.org/10.1302/0301-620X.103B2.BJJ-2020-1050.R1
2. Griffiths-Jones W, Chen DB, Harris IA, et al (2021) Arithmetic hip-knee-ankle angle (aHKA): An algorithm for estimating constitutional lower limb alignment in the arthritic patient population. Bone Jt Open 2:351–358. https://doi.org/10.1302/2633-1462.25.BJO-2021-0028.R1/ASSET/IMAGES/LARGE/BJO-2021-0028.R1-GALLEYFIG5.JPEG
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