Coronal alignment in Indian osteoarthritic knees: Predominance of varus apex-distal phenotypes highlights...

The coronal plane alignment of the knee (CPAK) classification, derived from the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO), is scarcely studied in Indian populations. This study evaluated CPAK phenotype distribution in Indian osteoarthritic (OA) knees and its association with demographics and early outcomes following robotic-assisted total knee arthroplasty (RATKA) using a functional alignment (FA) approach.

All RATKA done consecutively between January 2022 and September 2023 were included for this retrospective study. Patient's preoperative long-leg radiographs were analyzed to measure the medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), aHKA, and JLO. Knees were classified into nine CPAK phenotypes (Types I-IX) according to alignment category (varus ≤ -3°, neutral -3°-3°, and valgus ≥3°) and JLO orientation (apex-distal [AD], neutral, and apex-proximal [AP]). Chi-square/Fisher's exact tests assessed associations with age, gender, and operative side. Postoperative alignment restoration and early functional outcomes were evaluated at six months.

Finally, the sample was based on 947 end-stage OA (Kellgren-Lawrence Grade 4) knees from 604 Indian patients with a mean age of 61.7 ± 9.7 years; 65% were women. Varus alignment: 88.2% of knees, valgus: 11.8%, and none were neutral. CPAK Type I (varus with AD joint line) predominated (78.7%), followed by Types III (9.5%), VII (6.8%), and IX (5.0%). No statistically significant differences were found between genders (p = 0.088) or sides. Postoperatively, 60% of Type I knees retained their native alignment with correction with ±3° aHKA, while 18% were moderated toward Type II alignment. After 6 months, Knee injury and Osteoarthritis Outcome Score (KOOS) increased from 50.7±2.1 to 89.1±1.2, KOOS- Activities of Daily Living subscale increased from 41.6 ± 3.2 to 85.9 ± 1.3, and Forgotten Joint Score increased from 29.8±1.2 to 77.9±1.3 (all p < 0.05).

In this large-scale radiographic study of Indian OA knees, varus alignment with an AD joint line (CPAK Type I) was the most prevalent phenotype. Postoperative radiographic assessment showed alignment restoration within a physiologic range in most cases, accompanied by marked improvement in early functional outcomes.

Level IV - Retrospective observational study.