Total knee arthroplasty (TKA) serves as a standard intervention for severe knee OA, consistently improving functionality, mitigating pain, and augmenting patient satisfaction. Currently, TKA implants with posterior stabilized (PS) and bi-cruciate stabilized (BCS) designs are often employed during surgery with no consensus on the absolute superiority of one over the other. Additionally, the enhancement of daily activities post-surgery profoundly impacts the quality of life of TKA patients. It is reported that although patients recuperate their knee mobility within six months following surgery, deficits relative to CG persist. Specifically, tasks such as ascending slopes and stairs can be challenging due to increased knee abduction and extension moments. Bilateral discrepancies are also essential for TKA patients. Owing to compensatory strategies, TKA patients tend to over-rely on their contralateral limb for daily tasks, potentially heightening the risk of knee OA in that limb.Age-, gender- and BMI-matched three groups (20 each in posterior stabilized TKA, bi-cruciate stabilized TKA, and CG) were recruited and tested pre-op and 6-month post-op to perform walking on level, slope, and stairs, and two clinical tests (timed-up-go, 10-time sit-to-stand). Knee joint kinematics and kinetics variables were calculated from motion data and ground reactions captured at 120 Hz and 1200 Hz, respectively. Muscle activities of both low extremities were recorded using a wireless EMG system at 1500 Hz. A knee biomechanics index (KBI) was developed based on these variables relative to CG. The longitude comparison of KBI and the differences of KBI across various daily activities, bilateral differences of TKA patients and the differences of two TKA implants were identified and compared in this study. The participants undergoing TKA displayed notable post-op enhancements, particularly in the sagittal and frontal planes' range of motion and knee moments, underscoring a substantial recovery from their pre-op state. However, the degree of improvement diverged significantly based on the type of daily activity undertaken. Stair ambulation, for instance, posed greater challenges and distinctions compared to level or inclined walking. This discrepancy was quantitatively captured through the KBI, which registered significant advancements in all examined daily activities post-TKA, with the most considerable progress observed during level walking. The analysis between posterior stabilized and bi-cruciate stabilized TKA implants revealed minimal variations in outcomes concerning knee kinematics and muscle activities. However, a key differentiation emerged in the sagittal plane range of motion during stair ambulation, emphasizing the nuanced yet specific efficiencies of each implant type in practical scenarios. Notwithstanding these subtleties, both implant types manifested a credible record of pain alleviation and functional augmentation for recipients. For the bilateral differences, the study illuminated disparities in knee kinematics, kinetics, and quadriceps muscle activities between the involved limb and its contralateral counterpart. Although there was a significant improvement in the ratio of knee forces, such as a significant improvement in knee force ratios, the persistence of bilateral discrepancies six months post-op for unilateral TKA recipients cannot be overlooked. This enduring inequality was particularly evident during strenuous activities like the ten-time sit-to-stand test, where a progressive reduction in the ground reaction force ratio was recorded with each repetition, along with noteworthy observations in quadriceps muscle activity. This study can provide surgeons with comprehensive guidance on implant selection and offer therapists a robust framework for devising optimal rehabilitation protocols, prioritizing function restoration, and mobility enhancement.