Phenotyping the knee joint - a narrative review of current literature

Phenotyping of the knee joint has been established as an important pre- and postoperative measure to better describe the individual knee joint in terms of alignment, laxity, morphology, and kinematics. Therefore, this narrative review aims to provide a comprehensive analysis of the current literature on phenotyping to understand both the major benefits and the existing limitations. This narrative review was conducted according to the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines. A total of 38 studies were included. The included papers were categorized into two main groups, CPAK and functional knee phenotyping (FKP), of which the second group could be further subdivided into alignment, laxity, and morphology. The advantages and limitations were noted. Understanding the underlying knee phenotype in OA knees is crucial for a more personalized approach in TKA. The standardized use of the current phenotype systems, whether CPAK or FKP is key. The advantage of CPAK is that it is easy to apply in daily practice, but it is of limited value because it may omit a lot of important information. FKP, on the other hand, contains many more parameters, which makes it difficult for the majority of surgeons to integrate into their routine planning. However, as the knee is defined by multiple parameters in three dimensions, it is of utmost importance to integrate as many factors as possible for an optimal alignment in TKA.