Comparative analysis of posterior tibial slope measurements: Accuracy and reliability of radiographs and CT.

Introduction: This study aimed to evaluate the accuracy and reliability of posterior tibial slope (PTS) measurements obtained from radiographs and CT. PTS, particularly its differences in medial and lateral measurements, plays a crucial role in knee alignment, and inconsistencies in measurement techniques across different imaging modalities have raised concerns about accuracy. Materials and methods: This retrospective study included data from 98 Japanese patients legs and 324 Chinese patients legs. PTS was measured on long-leg and short-leg radiographs and CT. Two independent surgeons assessed the measurements, and the inter- and intra-observer reliability were evaluated. The primary outcome was the comparison of medial and lateral PTS measurements, while the secondary aim was to assess the impact of tibial length on measurement accuracy. Discussion: The study revealed that lateral PTS was consistently smaller than medial PTS, with an average difference of 1.2°-1.9°. Shorter leg radiographs tend to underestimate PTS compared to full-length tibial measurements. The correlation between measurements from short and long leg radiographs showed that PTS measurements were more prone to errors, which may be due to anatomical factors such as tibial bowing. Inter- and intra-observer reliability were good for medial PTS but poor to moderate for lateral PTS, especially when using radiographs. Conclusion: For accurate measurement of both medial and lateral PTS, surgeons should consider using additional examination methods such as CT and MRI. If PTS is to be measured on radiographs, the focus should be on the medial PTS, as it tends to provide more reliable results.