Distribution of knee alignment in the Italian arthritic population based on the CPAK classification

The CPAK classification categorizes coronal knee alignment matching the arithmetic hip-knee-ankle angle and joint line obliquity. While several studies have evaluated alignment variability in different populations, no data exist for the Italian population. This study aims to assess the distribution of CPAK classification in Italian patients undergoing TKA for osteoarthritis, with secondary objectives exploring gender differences and correlations with anthropometric parameters.

A retrospective analysis was conducted on 978 consecutive patients who underwent total knee arthroplasty or unicompartmental knee arthroplasty between May 2016 and April 2024. After excluding 284 patients, 620 patients were included in the study. Mechanical hip-knee-angle, Lateral Distal Femur Ange and Medial Proximal Tibial Angle were measured on long leg radiograph. Arithmetic HKA and Joint Line Obliquity were than calculated and patients were divided into the 9 phenotypes of the CPAK classification.

A total of 620 patients were evaluated: The mean age was 69.3 years. The mean BMI was 28.51. The mean mHKA was -4,63 (SD = 8,19) while the mean aHKA was -0.84° (SD = 5). The mean JLO was 174,18° (SD = 4.58). The three most frequent CPAK phenotypes were I (186; 30%), II (147; 23,7%), and III (126; 20,3%), indicating a prevalence of apex distal joint line obliquity. The most common alignment was varus. Female patients showed a greater tendency for valgus alignment (24,4%) compared to males (13%). No correlation was found between anthropometric parameters and alignment.

The CPAK classification distribution in the Italian osteoarthritic population is consistent to that reported in the literature. Level of evidence Level III.