Correlation of CPAK phenotypes with radiological alignment and functional outcomes after cruciate-retaining total knee arthroplasty: A retrospective study of 50 subvastus cases
Ashwin Taware, Amol Dhawale, Aditya KharwandikarAbstract
Background:
End-stage knee osteoarthritis is often managed with total knee arthroplasty (TKA), yet a meaningful minority of patients remain dissatisfied despite acceptable radiographs. This has raised questions about a single neutral mechanical target and renewed interest in coronal plane knee phenotypes.
Materials and Methods:
In this retrospective observational study, 50 consecutive cruciate-retaining TKAs performed via a subvastus approach by a single surgeon were analyzed at a tertiary center in India. Pre- and postoperative full-length hip–knee–ankle (HKA) radiographs were used to measure mechanical axis and classify knees with the Coronal Plane Alignment of the Knee (CPAK) system. Clinical outcomes included visual analogue scale (VAS) pain scores, Western Ontario and McMaster Universities Arthritis Index, and postoperative range of motion (ROM) at 15 days, 3 months, and 1 year.
Results:
Preoperatively most knees were varus and CPAK type I or III. Surgery produced a significant shift in the HKA angle toward neutral, with about 92% of knees within 177°–183° and postoperative phenotypes clustering in neutral type II and type V. VAS and WOMAC improved significantly, and ROM increased over time. Early outcomes showed phenotype-related differences: type II and type V were associated with better early ROM and, for type V, higher WOMAC scores, while pain and 1-year function improved across phenotypes.
Conclusion:
Mechanically aligned, cruciate-retaining TKA through a subvastus approach in this Indian varus-predominant cohort reliably normalized coronal alignment CPAK classification offers a valuable framework for predicting postoperative function and tailoring alignment strategies in TKA. Personalized surgical approaches that respect native knee anatomy yield superior patient-reported outcomes, enhanced satisfaction, and potentially improved implant longevity. Incorporating CPAK-informed strategies into surgical planning may reduce dissatisfaction rates and optimize long-term success in TKA patients.