Coronal plane alignment of knee (CPAK) classification in Indians undergoing total knee arthroplasty: Are there racial differences in phenotype distribution?

Optimizing alignment & balance strategies during Total Knee Arthroplasty (TKA) requires a comprehensive understanding of lower limb constitutional alignment. The coronal plane alignment of the knee (CPAK) classification system has become a widely adopted tool. This study aims to categorize arthritic knees in the Indian population using the CPAK categorization system and to investigate potential racial variations in the distribution of CPAK phenotypes. A retrospective observational study was done, including 378 patients (261 females, 117 males) with 500 arthritic knees. These patients underwent radiological evaluation using a standardized digital long-leg scannogram and various angles, which include the medial proximal tibial angle (MPTA), mechanical lateral distal femoral angle (mLDFA), and mHKA (mechanical hip-knee-ankle angle) had been measured. Both mHKA & arithmetic hip-knee-ankle angle (aHKA), as well as JLO, have been assessed. As per these measurements, the arthritic knees were classified into the nine previously described CPAK types. Among the 500 arthritic knees, the majority were classified as Type I (220 knees, 44 %) and Type IV (111 knees, 22.2 %). The mean aHKA was −4.70° ± 6.31°, and the mean JLO was 175.89° ± 5.31°, indicating a predominance of constitutional varus alignment having an apex-distal or apex-neutral JLO. When mHKA versus JLO was plotted according to the CPAK classification, similar findings were observed, with Type I (255 knees, 55 %) and Type IV (129 knees, 25.8 %) being the most prevalent. Significant variations were observed in the CPAK distribution among Indian patients undergoing TKA, predominating varus alignment and apex-distal or neutral joint line orientations (Types I and IV). This differs from the original CPAK study, where Type II was the most common phenotype. These outcomes give valuable insights into the patterns of arthritic knee alignment in the Indian population undergoing TKA, which may influence surgical planning and outcomes.