CPAK classification detect the real knee joint apex position in less than half of the knees

Yavuz Şahbat; Te-Feng Arthur Chou; Jae-Sung An; Fırat Gülağacı; Matthieu Ollivier

doi:10.1002/ksa.12175

CPAK classification detect the real knee joint apex position in less than half of the knees

Knee Surg Sports Traumatol Arthrosc. 2024 Apr 12. doi: 10.1002/ksa.12175. Online ahead of print.

Authors

Yavuz Şahbat^{1

2}, Te-Feng Arthur Chou^{1

3}, Jae-Sung An^{1

4}, Fırat Gülağacı^{1

5}, Matthieu Ollivier¹

Affiliations

¹ Institute du Mouvement et de l'appareil locomoteur, Hôpital Sainte-Marguerite, Aix-Marseille Université, Marseille, France.
² Erzurum Regional Training and Research Hospital, Department of Orthopaedics and Traumatology, Erzurum, Turkey.
³ Department of Orthopaedic Surgery, Medstar Union Memorial Hospital, Baltimore, Maryland, USA.
⁴ Department of Joint Surgery and Sports Medicine, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
⁵ Department of Orthopaedics and Traumatology, Faculty of Medicine, Trakya University, Edirne, Turkey.

PMID: 38613184
DOI: 10.1002/ksa.12175

Abstract

Purpose: Accurate assessment of the knee joint line is essential for surgeries involving the knee. The knee joint line obliquity (KJLO) is a radiological measurement that evaluates the position of the knee joint relative to the ground and is frequently used in preoperative planning and clinical follow-up. On the other hand, coronal plane alignment of the knee (CPAK) classifications assesses the joint line as the summation of the medial proximal tibial angle (MPTA) and mechanical lateral distal femoral angle (mLDFA). The purpose of this study is to determine the concordance of these two measurement techniques.

Methods: This cross-sectional study evaluated the long-leg standing radiographs (LSRs) of 164 healthy knees. The extremity KJLO and CPAK classification JLO were measured twice by two observers at 8-week intervals. The knee joint line apex positions (proximal, neutral and distal) of the two measurement techniques are compared (concordance or discordant). The intraobserver and interobserver reliability were examined using the intraclass correlation coefficient (ICC). Possible causes of the discordant were evaluated with univariate and multivariate logistic regression analysis.

Results: CPAK classification detected the KJLO apex position in 70 extremities (42.7%) only. Subgroups CPAK JLO detected 13.6% of the proximal apex, 20.4% of the neutral, and 90.7% of the distal apex (p < 0.01). Upon multivariate logistic regression analysis, the variable KJLO apex position (proximal, neutral vs. distal, odds ratio (OR) = 10.291, 95% confidence interval [CI] = 2.225-25.656, and (p < 0.01) was determined as a risk factor for discordant.

Conclusion: The CPAK JLO measurement technique can be misleading in defining the KJLO apex position and the concordance between them is less than 50%. It has a high tendency to misleadingly predict proximal and neutral apex positions, which can potentially have negative implications for assessing the joint line.

Level of evidence: Level I.

Keywords: coronal plane alignment of the knee (CPAK) classification; joint line orientation angle (JLOA); knee joint line obliquity (KJLO); mechanical alignment; medial proximal tibial angle.

Grants and funding

None