PURPOSE: Gait analysis was used to evaluate knee kinematics in patients who underwent successful primary total knee arthroplasty (TKA) using two modern bi-cruciate substituting designs. The knee joint was balanced intraoperatively using real-time sensor technology, developed to provide dynamic feedback regarding stability and tibiofemoral load. The authors hypothesized that major differences exist in gait parameters between healthy controls and post-TKA patients. METHODS: Ten patients who underwent successful TKA using bi-cruciate substituting designs were evaluated at a minimum of 9 months postoperatively using three-dimensional knee kinematic analysis; a multi-camera optoelectronic system and a force platform were used. Sensor-extracted kinematic data included knee flexion angle at heel-strike (KFH), peak midstance knee flexion angle (MSKFA), maximum and minimum knee adduction angle (KAA) and knee rotational angle at heel-strike. Multiple gait analysis data from the study group were compared to a group of ten healthy controls who were matched by age, sex and BMI. Clinical outcome in the TKA group was also measured using the Knee injury and Osteoarthritis Outcome Score (KOOS). RESULTS: Clinically, at final follow-up, a statistically significant difference in pain, general symptoms, and activities of daily living was seen between the groups. From a gait analysis standpoint, TKA patients had significantly less rotation at heel strike (p = 0.04), lower late stance peak extension moments (p = 0.02), and less Knee Adduction Angle excursion during swing phase (p = 0.04) compared to the control group. No statistically significant difference was observed for knee flexion angle at heel strike, knee adduction moment, or peak knee flexion moment between the groups. CONCLUSIONS: Modern bi-cruciate substituting TKA designs failed to reproduce normal knee kinematics. The lack of full knee extension during the stance phase, absence of the "screw-home mechanism" typical of an ACL functioning knee, and the reduced fluctuation in knee adduction angle during the swing phase still represent major proprioceptive and muscular recruitment differences between normal and replaced knees.