Department of Orthopaedic Surgery, Chonnam National University Hwasun Hospital, Chonnam National University Medical School, Hwasun, Korea.
Clin Orthop Surg. 2024 Jun;16(3):422-429. doi: 10.4055/cios23250. Epub 2024 Feb 20.
The Coronal Plane Alignment of the Knee (CPAK) classification system has been developed as a comprehensive system that describes 9 coronal plane phenotypes based on constitutional limb alignment and joint line obliquity (JLO). Due to the characteristics of Asian populations, which show more varus and wider distribution in lower limb alignment than other populations, modification of the boundaries of the arithmetic hip-knee-ankle angle (aHKA) and JLO should be considered. The purpose of this study was to determine the knee phenotype in a Korean population based on the original CPAK and modified CPAK classification systems.
We reviewed prospectively collected data of 500 healthy and 500 osteoarthritic knees between 2021 and 2023 using radiographic analysis and divided them based on the modified CPAK classification system by widening the neutral boundaries of the aHKA to 0° ± 3° and using the actual JLO as a new variable. Using long-leg standing weight-bearing radiographs, 6 radiographic parameters were measured to evaluate the CPAK type: the mechanical HKA angle, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), aHKA, JLO, and actual JLO.
From 2 cohorts of 1,000 knees, the frequency distribution representing all CPAK types was different between the healthy and arthritic groups. The most common categories were type II (38.2%) in the healthy group and type I (53.8%) in the arthritic group based on the original CPAK classification. The left and upward shift in the distribution of knee phenotypes in the original classification was corrected evenly after re-establishing the boundaries of a neutral aHKA and the actual JLO. According to the modified CPAK classification system, the most common categories were type II (35.2%) in the healthy group and type I (38.0%) in the arthritic group.
Although the modified CPAK classification corrected the uneven distribution seen when applying the original classification system in a Korean population, the most common category was type I in Korean patients with osteoarthritic knees in both classification systems. Furthermore, there were different frequencies of knee phenotypes among healthy and arthritic knees.
膝关节冠状面对线（CPAK）分类系统是一种全面的系统，它基于固有肢体对线和关节线倾斜（JLO）描述了 9 种冠状面表型。由于亚洲人群的特点，其下肢对线表现出比其他人群更多的内翻和更宽的分布，因此应该考虑修改算术髋膝踝角（aHKA）和 JLO 的边界。本研究的目的是基于原始的 CPAK 和改良的 CPAK 分类系统，确定韩国人群的膝关节表型。
我们回顾性地收集了 2021 年至 2023 年间 500 例健康和 500 例骨关节炎膝关节的前瞻性数据，使用放射分析，并根据改良的 CPAK 分类系统进行分组，该系统通过将 aHKA 的中性边界拓宽至 0°±3°，并将实际的 JLO 用作新变量。使用长腿站立负重位 X 线片，测量 6 个放射学参数来评估 CPAK 类型：机械 HKA 角、内侧胫骨近端角（MPTA）、外侧股骨远端角（LDFA）、aHKA、JLO 和实际 JLO。
从这 2 组 1000 个膝关节中，健康组和关节炎组的所有 CPAK 类型的频率分布不同。根据原始的 CPAK 分类，健康组最常见的类型为 II 型（38.2%），关节炎组最常见的类型为 I 型（53.8%）。重新建立中立 aHKA 和实际 JLO 的边界后，膝关节表型的分布在原始分类中的左移和上移得到了均匀纠正。根据改良的 CPAK 分类系统，健康组最常见的类型为 II 型（35.2%），关节炎组最常见的类型为 I 型（38.0%）。
尽管改良的 CPAK 分类纠正了在韩国人群中应用原始分类系统时出现的不均匀分布，但在两种分类系统中，韩国骨关节炎患者的最常见类型均为 I 型。此外，健康和关节炎膝关节之间的膝关节表型频率不同。
