Background: This prospective observational study was undertaken to look into the factors that affect the outcome of total knee arthroplasty and the short-term results of total knee replacements in complex knee pathologies. Methods: This prospective observational study was conducted between 2021 and 2023 at Owaisi Hospital and Research Centre, Hyderabad. A consecutive series of 12 total knee arthroplasties was performed on 12 patients at our institute using PFC Sigma endoprosthesis. The patients were assessed clinically and radiologically using the INSALL scoring system.  Results: The average pre-operative range of motion (flexion) was 45˚, with a highest of 120˚ and a lowest of 0˚. The average post-operative flexion was 102˚, with a highest of 130˚ and a lowest of 90˚. The average extension lag preoperatively was 18˚, and the average postoperative extension lag was less than 10˚. The average pre-operative knee score was 64.84, with the highest score of 91 and the lowest score of 40. The majority of the patients had a score in the range of 51–100. The average post-operative knee score was 136.84, with the highest score of 160 and the lowest score of 120. A majority of the patients had an improvement in score in the range of 101–150. At 6 months, follow-up relief was excellent in most patients; only 10 patients had anterior knee pain, and all the patients were able to walk more than 50 blocks post-operatively without any walking aid. Conclusion: Determining the factors resulting in a difficult knee helps in formulating an appropriate surgical approach, which results in a better functional outcome following total knee arthroplasty.