Is the coronal plane alignment of the knee (CPAK) classification useful to plan individualized total knee arthroplasty surgery for the Spanish population? A critical analysis of the CPAK classification

Abstract

Introduction: The CPAK classification aims to categorize knee phenotypes. The original study was based on Australian and Belgian population, but significant variation in CPAK distribution exists between different geographic areas. The primary objective is to evaluate knee phenotypes of osteoarthritic Spanish population based on the CPAK system. The secondary objective is to compare the Spanish CPAK distribution with that observed in the original study to analyse if proposing modifications is necessary when applying the classification to our population. Finally, we aim to critically analyse the utility of this classification to plan individualized TKA.

Methods: It is a cross-sectional observational study analysing radiological datasets from 121 patients with knee osteoarthritis treated with a Mako assisted TKA in three Spanish institutions. The preoperative lower limb CT-scan was used to measure the MPTA and LDFA of each patient. Then, the aHKA (MPTA-LDFA) and JLO (MPTA+LDFA) were calculated to categorize patients into the nine CPAK phenotypes.

Results: The commonest knee phenotypes of osteoarthritic Spanish population were the distal apex JLO CPAK types (74%: II (28%), I (23%) and III (23%)). No patient presented a proximal apex type (VII, VIII and IX). The 30% of the patients had a varus alignment and 26% a valgus. No relevant differences were found between the Spanish CPAK distribution and that observed in the original study.

Conclusions: No modifications to the CPAK classification should be necessary for the Spanish population. The CPAK classification can be useful to describe and categorize osteoarthritic patients. However, relevant limitations have been found to the classification, questioning its utility to plan and guide individualized TKA surgery.

Keywords: Alignment; Alineación; Artroplastia total de rodilla; Coronal plane alignment knee classification (CPAK); Fenotipo; Phenotype; Prótesis total de rodilla; Robotics; Robótica; Total knee arthroplasty (TKA); Total knee replacement (TKR).