Coronal plane alignment of knee joint (C.P.A.K.) classification in Indian population-study of a new classification system in Indian knees

Abstract

Background: Distribution of CPAK types in Indian knees will help surgeons better understand management of knee arthritis using concept of Kinematic alignment (K.A.). C.P.A.K. uses a matrix of 9 phenotypes of knees based on arithmetic hip knee ankle angle (aHKA) and Joint Line Obliquity (JLO). Methods: A radiological analysis of 200 healthy knees (HC) and 250 osteoarthritic knees (OC) was done and were classified based on C.P.A.K. classification. Primary outcomes include descriptive analysis of both groups, and comparison between frequencies of types within each group. Results: The commonest CPAK types in Healthy group were type 5, type 2, type 1. For arthritic group, common types in order were type 1, type 4 and type 2. Varus CPAK types (1,4,7) accounted for 34 % of HC types while 59 % of OC type, with odds of developing osteoarthritis in type 1 CPAK being 2.84 while that for type 4 were 2.02. Out of 450 knees studied 216 (48 %) accounted for varus alignment. Conclusion: C.P.A.K. classification can be used to understand the targets for TKR in Indian population. Constitutional varus being commoner in Indian knees (48 %) than their western counterparts implies that majority of Indian knees are in constitutional varus dynamics, hence K.A. caters to majority of the population. Arthritic Indian populations are predominantly of types C.P.A.K. 1 (34 %) and 4 (22 %). Further research is needed to understand which Indian knee types benefit the most from KA TKR.

Keywords

• Kinematic alignment
• Coronal plane alignment of knee joint
• Joint line obliquity
• Arithmetic hip knee ankle angle
• Constitutional varus