2025 ISAKOS Biennial Congress ePoster
Impact of Aging and Knee Osteoarthritis on Lower Limb Alignment and CPAK Classification: Gender Differences in a Japanese Cohort
Kento Harada, MD, Sendai-Shi, Miygi-Ken JAPAN
Masayuki Kamimura JAPAN
Takashi Aki, PhD, Sendai, Miyagi JAPAN
Shunsuke Utsumi, MD, Sendai City, Miyagi JAPAN
Toshimi Aizawa, Sendai, Miyagi JAPAN
Department of Orthopaedic Surgery, Tohoku University School of Medicine, Sendai, Miyagi, JAPAN
FDA Status Not Applicable
Summary
In the Japanese population, aging and the progression of knee osteoarthritis impact coronal alignment and CPAK classifications differently across genders. Young Japanese exhibit similar CPAK distributions as other races; however, differences become notable in those with osteoarthritis, suggesting potential racial variations in CPAK classifications.
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Abstract
Background
The Coronal Plane Alignment of the Knee (CPAK) classification system, introduced by MacDessi in 2021, provides a structured approach for categorizing the coronal plane alignment of the lower extremities. While CPAK classifications have been explored in multiple countries, there are no existing studies on the CPAK classification among the Japanese population unaffected by knee osteoarthritis (OA), nor on how aging and the progression of OA impact the distribution of CPAK classifications. This study investigates the impact of age and knee OA on the coronal plane alignment of the lower extremities in Japanese males and females, utilizing the CPAK classification system.
Methods
A cross-sectional analysis was conducted with 150 male and 150 female patients. Participants were divided into three groups according to age and OA progression. The medial distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA) were measured using standard digital long-leg radiographs. Arithmetic Hip-Knee-Ankle (aHKA) angle and joint line obliquity (JLO) were calculated, and the CPAK classification was performed to verify the distribution among the three groups. Statistical differences were assessed using Bonferroni correction and t-tests.
Results
The results showed increased varus alignment of the mean mLDFA correlated with OA in both genders and with aging in males. The mean mMPTA did not change in males but shifted towards varus in females with both aging and OA. Both genders demonstrated a constitutional varus alignment with the progression of knee OA (males: 1.3±2.4° to -3.5±3.7°; p<0.001, females: -1.2±3.2° to -3.6±2.9°; p<0.001). However, this trend with aging was observed only in females (0.0±2.5° to -1.2±3.2°; p=0.049). JLO maintained its apex distal position with aging and OA progression in all subjects. The study further revealed a notable transition from CPAK Type II to Type I with OA progression in both genders, influenced additionally by aging in females.
Conclusion
Aging affects coronal alignment and CPAK classification differently across genders. With OA progression, there was a shift towards smaller aHKA, while JLO remained unchanged. Compared to other races, young Japanese exhibit similar CPAK distributions, but distinct differences appear in OA-affected individuals, highlighting potential racial variations in CPAK classifications.