Coronal Plane Alignment of the Knee Classification in the Brazilian Population: A Radiographic Analysis of Patients With Primary Knee Osteoarthritis Undergoing Total Knee Arthroplasty
F.A.C. Menegassi, R.E. De Paula, D.P. Da Motta, J.L.R. De Faria, N.T. Cavanellas, P.A.V. MaiaObjectives:
To identify the incidence and distribution of lower limb deformities according to the Coronal Plane Alignment of the Knee (CPAK) classification in patients with primary knee osteoarthritis treated with total knee arthroplasty (TKA) at a national reference center.
Methods:
This retrospective cohort study evaluated 476 knees of patients who underwent primary TKA between 2023 and 2025. Preoperative standing anteroposterior radiographs including the hip, knee, and ankle joints were analyzed. Angular parameters were measured according to Paley’s method using dedicated software (PeekMed), including mechanical lateral distal femoral angle, mechanical medial proximal tibial angle, hip–knee–ankle (HKA) angle, and joint line obliquity (JLO). Patients were classified according to the CPAK system. Only patients with nontraumatic primary osteoarthritis and adequate radiographs were included.
Results:
The cohort comprised 164 women and 74 men, with a mean age of 68.9 ± 9.1 years. Men demonstrated a more varus HKA alignment than women. Joint line obliquity was similar between sexes, with a predominance of a distal apex. CPAK type I was the most prevalent pattern (39.3%), followed by types II (16.6%), III (15.3%), and IV (14.9%). Proximal apex phenotypes (types VII–IX) were rare.
Conclusion:
Brazilian patients with primary knee osteoarthritis undergoing TKA demonstrate wide variability in coronal alignment and joint line obliquity. The predominance of CPAK type I, followed by a substantial proportion of intermediate types, indicates that classic neutral mechanical alignment does not represent most osteoarthritic knees.