A biomechanical analysis of the single-radius and multi-radius total knee arthroplasty systems for the sit-to-stand and stand-to-sit
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The purpose of the study was to investigate the effect of the design differences between the multi-radius (M-RAD) total knee arthroplasty (TKA) and the single-radius (S-RAD) TKA systems on the functional performance for the sit-to-stand and stand-to-sit movements. Sixteen participants with unilateral posterior stabilized TKA (8 M-RAD and 8 S-RAD) were involved in the study. Three dimensional kinematic and EMG analysis of the sit-to-stand and stand-to-sit tasks were conducted. One-way ANOVA analyses were performed (á = 0.05). Compared to the S-RAD group, for the sit-to-stand movement, the M-RAD group exhibited greater movement time, trunk flexion, and a tendency for trunk flexion velocity. The M-RAD TKA limb had a tendency for a briefly distinct abduction (ABD) movement during trunk flexion and a greater adduction (ADD) displacement during knee extension as compared to the S-RAD group. Also, the M-RAD group displayed higher TKA knee flexor and extensor activations than the S-RAD group. For the stand-to-sit, the M-RAD group exhibited greater ABD displacement with the ABD peak occurring at a significantly later time in comparison to the S-RAD group. In addition, the M-RAD TKA limb demonstrated greater knee flexor and extensor activations than the S-RAD TKA limb. As expected, the S-RAD group performed differently from the M-RAD group. The S-RAD group used less effort to accomplish sit-to-stand and stand-to-sit by showing less movement time and knee extensor activation. However, the M-RAD group exhibited compensatory adaptations during the trunk flexion of the sit-to-stand. The greater knee extensor EMG revealed the fact that the M-RAD group had difficulty in performing the sit-to-stand and stand-to-sit movements. Furthermore, the S-RAD TKA knee was more stable than the M-RAD TKA knee during the sitto- stand and stand-to-sit tasks because the S-RAD TKA knee displayed less ABD/ADD displacement and knee flexor co-activation EMG. The multi radii design might account for the instability of the M-RAD TKA knee as the short radii used in the mid knee flexion could cause collateral ligaments to lose tension. In conclusion, the S-RAD TKA design has advantages to facilitate knee extension movements and maintain adequate collateral ligaments’ tension.