Abstract: Background: The purpose of this study is to formulate a simple and effective method of calculating native joint line and Posterior Condylar Offset (PCO) in proper lateral modern lateral radiographs of knee joint with minimal magnification coefficient.
Methods: Knee joint line is measured from a. Posterior condylar flare and b. Tibial tuberosity. Line (A) was drawn from posterior cortex of femur that crossed the flare of posterior condyles. Joint line was measured by a perpendicular line (B) from the proximal most point of tibial tuberosity to the line joining the posterior cortex femoral line on lateral view. Posterior condylar offset: PCO was measured (B) relative to the tangent of the posterior cortex of the femur. The ratio was calculated from these measurements in relation to KSS also. Patients attending to Nizam’s Institute of Medical Sciences, Hyderabad, in orthopaedic OPD with ideal body mass index who were evaluated for knee radiographs are included in the study after taking proper consent (n=210). Insta RIS PACS software is used to measure the parameters.
Results: The mean joint line measured was 16 mm (range 14 to 18) with 3.0 as standard deviation and the mean PCO was 25mm (Range 19 to 31) with a standard deviation of 3.0. The KSS score had a mean of 85 (Range 80 to 90) indicating excellent score with standard deviation of 2.0. Joint line ratio was 95% Confidence interval (CI) and the ratio for PCO was also 95% CI. There was a significant difference in the measured joint line between genders.
Conclusion: Using the current measuring method related to standard fixed bony land marks (Posterior femoral line, posterior femoral condyle and tibial tuberosity) which are unaffected even post-surgery the restoration of native joint line and PCO is reliable and reproducible.
