Correlation of posterior tibial slope with metaphysio-diaphyseal angle in total knee arthroplasty: A radiological study

BACKGROUND: Posterior tibial slope (PTS) is an important factor affecting postoperative range of motion (ROM) following total knee arthroplasty (TKA). Metaphysio-diaphyseal angle (MDA) is a new entity defined as angle between proximal anatomical axis and metaphyseal axis of tibia. This study was undertaken to determine PTS in Indian patients and find its correlation with MDA of tibia. Accuracy of extramedullary jigs and the influence of MDA on the accuracy was also evaluated. This study is a retrospective analysis of prospectively collected data in a tertiary healthcare center. MATERIALS AND METHODS: Data of 100 consecutive patients undergoing TKA in a single center by a single surgeon was analyzed. Posterior cruciate ligament (PCL) substituting TKA was done with same jig to achieve different PTS in different patients. MDA, preoperative PTS and postoperative PTS were calculated. The data was analyzed using appropriate statistical analysis. RESULTS: Mean preoperative PTS was 11.64° and mean MDA was 23.76° with a strong correlation between them (Pearson's coefficient 0.72). Extramedullary jigs were accurate in 53% cases. In remaining 47%, postoperative PTS was less than planned PTS in 30%, and more in 17%. Mean postoperative PTS was 2.54°. In patients with MDA < 20°, postoperative PTS was significantly less (P = 0.0176) compared with those with MDA > 20°. CONCLUSIONS: The study establishes the positive correlation between MDA and PTS in Indians; and that MDA is an independent factor affecting accuracy of extramedullary jigs in TKA.