Accuracy and Validity of Sharma's Venn Diagram Method for Assessment of Tibial Component Rotation in Total Knee Arthroplasty.

Background: Malrotation of the tibial component in a total knee replacement leads to anterior knee pain, patella dislocations, extensor mechanism disruptions, knee stiffness and prosthesis loosening. Techniques like free-floating technique, medial 1/3 rd of the tibial tubercle, medial border of the tibial tuberosity, Akagi's line, transcondylar line of tibia, posterior condylar line of tibia, midsulcus of tibial spines, curve on curve technique have been advocated. None of these have been shown to be accurate and reproducible. We developed a novel 'Sharma's Venn Diagram' method to assess the tibial component rotation. Methods: Fifty-two consecutive knee replacements were included in a prospective observational study. The average age of the study group was 53.6 years (48-76 years) Thirty-one were females and 3 were males. The patients were followed a minimum of one years (max 2 years, average 1.8 years). 'Sharma's Venn diagram Method (C)' was compared to free-floating method (F) and post-op CT scans using Berger protocol (B). Results: Tibial rotation calculated using Sharma's Venn diagram method (C) coincided with the final component placement in 50/52 knees. The free floating method (F) coincided with method (C) in 30/52 knees with an average 4.8° external rotation in 5 knees and an average of 5.2° internal rotation in 17 knees. Bland Altman method was used to compare method (C) with Method (F), The difference was statistically significant Conclusion: Sharma's Venn diagram method is reliable, accurate and easily reproducible by any surgeon performing tkr and correlates with postoperative 2D CT-based assessment of tibial component rotation. Level II Study: Prospective observational study.