Summary

In our study 64% of TKA changed their CPAK type postoperatively. There was no significant difference in patient reported outcomes between those who changed CPAK type and those who did not. There was no significant difference between the ATT and TRI groups for the distribution of post operative CPAK types.

Abstract

Background

The concept of classification of coronal plane alignment of the knee (CPAK), based on constitutional alignment and joint line obliquity is quickly gaining popularity for use in planning total knee arthroplasty (TKA). The aim of this study was to determine if CPAK changes from baseline to post operative affected patient reported outcome of TKA.

Methods

The study group of 83 consecutive patients underwent TKA under the care of a single surgeon between 2022 and 2024, consented to participation in a prospective research database and had both preoperative and postoperative EOS scan to assess CPAK. Participants were allocated to groups according to the prosthesis they received, either the Attune with Velys robotic system (ATT) or Triatholon with Mako robotic system (TRI). Coronal alignment measures were assessed using digital imaging software and classified into CPAK phenotypes. Subjects completed baseline patient reported outcome measures (PROMs), including Oxford Knee Score, KOOS-12 and EQ5D. Participants repeated PROMS at 12 months with additional questions regarding satisfaction. PROMs were compared between those who did and did not change CPAK alignment postoperatively with non parametric tests. The distribution of CPAK alignment, and the proportion who demonstrated a change in alignment was compared between the ATT and TRI groups.

Results

There were 47 participants in the ATT group and 36 in the TRI group. There was no significant difference between the groups in side of procedure (p=0.818), gender (p=0.510) or mean age (p=0.227). The most common preoperative CPAK type was Type I, II, and V. A change in CPAK alignment was observed in 64%, with no significant difference between the ATT and TRI groups (p=0.354). There was no significant difference between those who did and did not change CPAK type for baseline Knee Scores (P>0.569), post operative Knee Scores (p>0.749), change in Knee Scores (p=0.613) or satisfaction with the outcome of surgery (p=0.715). The distribution of preoperative CPAK types was significantly different between the ATT and TRI groups at baseline (p=0.001), but was not significantly different between the 2 groups at 1 year (p=0.209).

Conclusions

In our study 64% of TKA changed their CPAK type postoperatively. There was no significant difference in patient reported outcomes between those who changed CPAK type and those who did not. There was no significant difference between the ATT and TRI groups for the distribution of post operative CPAK types.