Background: Key to a successful outcome of total knee arthroplasty (TKA) is to attain optimum alignment, adequate balance, and deformity correction. In primary TKA, this can be achieved efficiently by posterior stabilized (PS) design with or without the sub-periosteal release. However, certain circumstances such as post-traumatic arthritis are often associated with severe deformities with a significant bone defect, stiffness, and instability. Such deformities are extremely difficult to balance with soft tissue release only and require additionally constrained prostheses even in primary TKA. In such situation, constrained condylar knee (CCK) design is the ultimate choice. This study primarily aimed to report on clinical outcome, regain of function, and complication of patients who underwent primary CCK-TKA for severe deformity of the knee secondary to post-traumatic arthritis. The secondary aim was to find out the mid-term prostheses survival. Methods: Between February 2007 and November 2013, 38 consecutive patients with post-traumatic arthritis of the knee received cemented primary CCK-TKA. Thirty-four patients (21 men and 13 women) who had a minimum of 3 years follow-up were included in this retrospective study. We used Knee Society Score (KSS), Hospital for Special Surgery (HSS) score, and roentgenographic evaluation form to assess the patients. Prostheses survival was assessed using Kaplan-Meier's survival analysis. Results: Patients were followed up for an average duration of 6.47 years. KSS knee score improved from 44 points (23-68) pre-operatively to 91 points (76-100) post-operatively [P < 0.001]. The average KSS functional score improved from 49 points (20-75) pre-operatively to 91 points (65-100) post-operatively [P < 0.001]. The average HSS score improved from 51 points (27-83) pre-operatively to 91 points (75-100) post-operatively [P < 0.001]. Similarly, the average ROM improved from 68.09 degrees +/- 35.99 degrees (0 degrees-120 degrees) to 113.68 degrees +/- 8.90 degrees (100 degrees-130 degrees) post-operatively [P < 0.001]. The average hip-knee-ankle (HKA) angle was 176.88 degrees +/- 14.48 degrees (135 degrees-199 degrees) pre-operatively and 180.24 degrees +/- 1.77 degrees (175 degrees-184 degrees) post-operatively. Radiolucencies were evident in 13 knees, mostly on the tibial side. Prostheses survival was 94.7% at a mean follow-up of 6.47 years. Conclusion: Despite severe deformity, instability, and stiffness at a relatively young age, mid-term follow-up of primary CCK-TKA in post-traumatic arthritis provides satisfactory clinical and functional outcomes with 94. 7% prostheses survival. However, it is not without complication.