Enhancing the radiological classification system from the distal femur to the proximal tibia.

Objectives: This study aims to identify anatomical variants of the proximal tibia shaft and to develop a novel classification system for proximal tibia.
Patients and Methods: Between October 2019 and April 2020, a total of 200 patients with standard knee anteroposterior radiographs were included in this study. We measured the inner diameter of the tibia 16 cm distally from the tibial plateau and 3 cm distally from the tibial spine. The ratio between these two measurements was applied as the novel index ratio.
Results: A total number of 197 patients (100 males and 97 females) with a median age of 68 years (range, 21 to 89 years) were included in the final analysis. According to the 25 ^th and 75 ^th percentiles, three groups were clustered for each sex. A higher distribution of the type B pattern was found in female and male patients. However, type A with a narrow inner diaphyseal diameter was less common in female patients. The median intraobserver reliability for rater 1 was 0.998. The inter-observer reliability was high (intraclass correlation coefficient: 0.998). There was a moderate correlation between the anteroposterior (AP) diameter and height (r=0.568) and a low correlation between the AP diameter and weight (r=0.376). The novel index shows no significant correlation between the index ratio and height (r=0.082), weight (r=0.014) or body mass index (r=-0.038).
Conclusion: The novel classification presents three different types of tibia for each sex: type C has a wider inner diaphyseal diameter compared to type A with a narrow inner diaphyseal diameter. Type B has the widest distribution among the subjects.