Retrospective study of asymmetric vs symmetric tibial plates and ultracongruent vs posterior stabilized inserts in Indian population: An Indian experience of Natural Knee II.

BACKGROUND: Results of asymmetric tibial base plates vs symmetric tibial base plates and ultracongruent insert vs posterior stabilized insert in Indian population.

METHODS: A total of 47 knee replacements with mean age of 65.2 years in 38 patients (16 males and 22 females) between 2007-2011 were included. Natural Knee II (21 models) were compared with 26 models of other knees (12 PFC-Sigma, one PFC-RPF, 10 Nexgen and three Vanguard).

RESULTS: The ultracongruent insert of NK II lead to creation of greater post-op mean flexion deformity of 18° (range 15-20°) as compared to 5.8° (range 5-8°) in other knees with PS insert ( P  < 0.001, confidence limit of 24.2-0.1). After 3 months NK II patients had a lower mean post-operative knee score of 87 as compared to mean post-operative knee score of 96 ( P  < 0.001, confidence limit of 17.9-0.1) in the non-NK II patients because of greater points deductions due to the creation of greater mean flexion deformity. When NO implant overhang is accepted on medial side, asymmetric tibial base plates leaves large portions of peripheral lateral tibial plateau uncovered by implant; decreasing the implant bone surface area ratio of Knee Society Radiographic Assessment Criteria. Similar problem is not encountered with symmetric tibial base plates.

CONCLUSION: Symmetric and not asymmetric tibial base plates provide greater bone coverage in Indian (ethnic Punjabi) population when no implant overhang is accepted. Further use of NK II was discontinued after just 21 cases in the interest of the patients.