Summary

CPAK Type I was the most common classification in Japanese osteoarthritis patients (70.4%). KA-TKA preserve JLO while maintaining ligament balance. These features may contribute to the results of KA-TKA.

Abstract

Objective

The coronal plane alignment of the knee (CPAK) classification is a coronal plane alignment classification consisting of nine phenotypes based on joint obliquity and lower limb alignment. In this study, we examined the changes in CPAK classification and its characteristics before and after surgery in Kinematic alignment (KA) TKA.

Method

Twenty-seven knees (male:female = 3:24, mean age 76) who underwent True KA-TKA from September 2021 to July 2022 were included. The aHKA (arithmetic HKA = MPTA-LFDA: varus < -2°, neutral = 0±2°, valgus > 2°) and JLO (joint line obliquity = MPTA + LFDA: apex distal<177°, neutral=180±3°, apex proximal>183°) were measured from long leg radiographs before and after surgery, and the lower limb alignment was classified based on the combination of these measurements. The frequency of each CPAK phenotypes and pre- and postoperative changes were examined.

Results

The pre- and postoperative changes in CPAK classification were Type I; 70.4% to 44.4%, II; 11.1% to 29.6%, III; 7.4% to 11.1%, IV; 11.1% to 11.1%, V; 0% to 3.7%, and VI to IX; 0% to 0%. The changes in aHKA were varus; 81.5% to 55.6%, neutral; 11.1% to 33.3%, and valgus; 7.4% to 11.1%, and the changes in JLO were apex distal; 88.9% to 85.2%, neutral; 11.1% to 14.8%, and proximal; 0% to 0%. JLO was preserved in 96.3% of the cases.

Discussion

According to a previous report (Toyooka, 2022), Type I was the most common CPAK classification in Japanese patients with knee osteoarthritis (53.8%), and similarly Type I was the most common in the present study (70.4%). KA-TKA was characterized by the preservation of JLO.
In Japanese patients with strong varus deformity, mechanical alignment technique often requires excessive soft tissue dissection to achieve neutral alignment and JLO, whereas KA technique preserve JLO while maintaining ligament balance. Many favorable clinical results of the KA-TKA have been reported in recent years, and these features in this study may contribute to the clinical results of the KA-TKA.