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. 2024 Jan 2;36(1):1.
doi: 10.1186/s43019-023-00204-3.

Preserving coronal knee alignment of the knee (CPAK) in unicompartmental knee arthroplasty correlates with superior patient-reported outcomes

Sung Eun Kim #  1 , Kuk-Ro Yun #  2 , Jae Min Lee  2 , Myung Chul Lee  1   2 , Hyuk-Soo Han  3   4
Affiliations

Preserving coronal knee alignment of the knee (CPAK) in unicompartmental knee arthroplasty correlates with superior patient-reported outcomes

Sung Eun Kim et al. Knee Surg Relat Res. .

Abstract

Background: The optimal alignment target for unicompartmental knee arthroplasty (UKA) remains controversial, and literature suggests that its impact on patient-reported outcome measures (PROMs) varies. The purpose of this study was to identify the relationship between changes in the coronal plane alignment of the knee (CPAK) and PROMs in patients who underwent UKA.

Methods: A retrospective analysis of 164 patients who underwent UKA was conducted. The types of CPAK types categorized into unchanged, minor (shift to an adjacent CPAK type, e.g., type I to II or type I to IV), and major changes (transitioning to a nearby diagonal CPAK type or two types across, such as type I to V or type I to III). PROMs were assessed preoperatively and 1 year postoperatively using the Hospital for Special Surgery (HSS) scores, Knee Society (KS) scores, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Forgotten Joint Scores (FJS). Comparison was performed between patients who experienced and who did not experience any changes in the CPAK.

Results: Patients with preserved native CPAK alignment demonstrated significantly superior 1 year postoperative outcomes, with higher HSS, KS knee, and WOMAC pain scores (p = 0.042, p = 0.009, and p = 0.048, respectively). Meanwhile, the degree of change in CPAK did not significantly influence the PROMs, and patients who experienced minor and major changes in the CPAK showed comparable outcomes.

Conclusion: Preserving the native CPAK in UKA procedures is important for achieving favorable clinical outcomes at 1 year postoperative. The extent of change in the CPAK type exerted a limited impact on PROMs, thus emphasizing the importance of change in alignment itself.

Keywords: Coronal plane alignment; Patient-reported outcome measures; Unicompartmental knee arthroplasty.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Radiologic parameter measurements: A Preoperative MPTA, B preoperative LDFA, C postoperative MPTA, and D Postoperative LDFA. In C and D the joint lines were measured using a line extending from the distal end of the femoral component to the center of the lateral joint space. MPTA, medial proximal proximal tibial angle; LDFA, lateral distal femoral angle
Fig. 2
Fig. 2
Preoperative and postoperative distribution of coronal plane alignment of the knee (CPAK) types
Fig. 3
Fig. 3
Heat map illustrating the transition of CPAK types from preoperative to postoperative. The y axis represents preoperative CPAK types, while the x axis represents postoperative CPAK types. Each cell in the heat map corresponds to the number of patients who transitioned from a specific preoperative CPAK type to a specific postoperative CPAK type. The darkness of the cell indicates the number of patients in each category, with darker cells representing a higher number of patients. CPAK, Coronal plane alignment of the knee; CPAKpre, preoperative CPAK; CPAKpost, postoperative CPAK
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