Knee impairments: Comparison between new clinical classification by cluster analysis and movement system impairment model.

Background: Although Movement System Impairment (MSI) model classifies patients with knee impairments, it has some limitations. This study compares MSI model with a new Partitioning Around Medoids (PAM) model in knee pain patients.

Methods: In this cross-sectional study, knee movement impairments (signs) and symptoms. (pain) of 200 patients were studied in eight different functional positions. After modification of impairments, the examinations were repeated to record the changes in symptoms. The patients were then classified based on the signs and symptoms firstly by MSI model and secondly using PAM clustering by R software.

Results: PAM model has a similar acceptable grouping compared to MSI because most patients are in 4 similar categories in both methods: valgus, varus, hyperextension and hypomobility. However, due to low discriminative power of the tests used for finding hypermobility and patellar dysfunctions, these sub-clusters are absent in PAM model. Instead, two new sub-clusters of self-management and valgus with hypomobility were found. Most importantly, the PAM model sorted the signs and symptoms based on their discriminative power and eliminated trivial tests so that the therapist can classify patients more quickly by performing clinically relevant tests.

Conclusion: The new PAM method can be advantageous for therapists since it defines the importance of signs over symptoms in examination, prioritizes examination tests, and outlines tests with lower discriminative power. In PAM model, patients in the hypermobility and patellar subgroups of MSI model merged into other sub-clusters due to low discriminating power of their characteristics.