Distribution and gender-specific differences of coronal plane alignment of healthy knee.

Background: Understanding optimal prosthesis alignment in TKA remains crucial despite ongoing debate. While current research focuses on osteoarthritic knees, a gap exists in characterizing healthy young adult knees in Asians. This study aims to fill this gap by identifying the distribution of CPAK phenotypes in this population, including potential gender variations and individual differences.

Methods: A total of 390 knees from 195 young adults aged 20 to 35 years without knee pain who underwent hip-knee-ankle radiography were prospectively collected between February 2024 and March 2024. The average MPTA, LDFA, aHKA, and JLO were measured. The overall CPAK distribution was analyzed to assess gender variations and individual differences. On average, participants were 25.7 years old, 165.7 cm tall, and had a BMI of 23.6 kg/m². LDFA, MPTA, aHKA, and JLO averaged at 86.8°, 87.2°, 0.3°, and 174.0°, respectively.

Results: This study demonstrates significant differences in knee alignment between men and women, as measured by the CPAK system. While zone II was the most common overall (43.3%), the distribution of CPAK zones varied by gender, with men exhibiting a higher prevalence of distal apex point alignments (89.9%) and women having a higher prevalence of CPAK zone V (18.3%). Finally, analysis of paired knees revealed a comparable zonal distribution for both genders (approximately 56%).

Conclusion: This study examined CPAK distribution in young Asian adults without knee osteoarthritis and identified potential sex-based variations. The findings suggest a predominance of distally pointed CPAK (76.9%) and a possible benefit for slightly varus tibial cuts during TKA in this population for optimal joint alignment. Additionally, gender-specific considerations should be incorporated into knee alignment assessments and treatment planning.

Level of evidence: II, A prospective descriptive study.