Clinical utility of markerless motion capture for kinematic evaluation of sit-to-stand during 30 s-CST at one year post total knee arthroplasty: a retrospective study

BACKGROUND: Although the importance of kinematic evaluation of the sit-to-stand (STS) test of total knee arthroplasty (TKA) patients is clear, there have been no reports analyzing STS during the 30-s chair sit-up test (30 s-CST) with a focus on kinematic characteristics. This study aimed to demonstrate the clinical utility of kinematic analysis of STS during the 30 s-CST by classifying STS into subgroups based on kinematic parameters, and to determine whether differences in movement strategies are expressed as differences in clinical outcomes. METHODS: The subjects were all patients who underwent unilateral TKA due to osteoarthritis of the knee and were followed up for one year postoperatively. Forty-eight kinematic parameters were calculated using markerless motion capture by cutting STS in the 30 s-CST. The principal components of the kinematic parameters were extracted and grouped by kinematic characteristics based on the principal component scores. Clinical significance was examined by testing whether differences in patient-reported outcome measures (PROMs) were observed. RESULTS: Five principal components were extracted from the 48 kinematic parameters of STS and classified into three subgroups (SGs) according to their kinematic characteristics. It was suggested that SG2, using a kinematic strategy similar to the momentum transfer strategy shown in previous studies, performed better in PROMs and, in particular, may be associated with achieving a “forgotten joint”, which is considered the ultimate goal after TKA. CONCLUSIONS: Clinical outcomes differed according to kinematic strategies used STS, suggesting that kinematic analysis of STS in 30 s-CST may be useful in clinical practice. TRIAL REGISTRATION: This study was approved by the Medical Ethical Committee of the Tokyo Women’s Medical University (approval number: 5628 on May 21, 2021). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12891-023-06364-3.