A new CT-based classification system for posterior cruciate ligament tibial avulsion fractures: a nationwide multicenter study.

Background: The Meyers-McKeever two-dimensional classification has been widely used in diagnosing and treating posterior cruciate ligament avulsion fractures since its introduction in 1959. However, because of image overlap and obscuration on knee radiographs, the type of avulsion fracture injury is often not identified, which can lead to misdiagnosis. CT has a higher overall confidence in size assessment, displacement, and degree of comminution of the posterior cruciate ligament avulsion fracture block compared with X-ray. Therefore, this study aims to propose a new classification system based on CT for posterior cruciate ligament avulsion fractures.

Methods: This multicenter study evaluated 523 patients with posterior cruciate ligament avulsion fractures admitted between July 2018 and July 2023 at nine medical centers. The new CT-based classification system, the Dong classification system, includes 2 major types and 7 subtypes. Furthermore, the inter- and intra-observer reliability of this classification system were compared to the Meyers - McKeever classification system by 4 observers (Kappa coefficient, K-value) to assess the reproducibility of the Dong-classification system for posterior cruciate ligament avulsion fractures.

Results: A total of 446 patients were eligible for inclusion criteria; 29 patients (6%) could not be classified through the Meyers - McKeever classification system, but all the cases were classifiable through the Dong classification system. The most common type of posterior cruciate ligament avulsion fracture is Type Ic, with 176 cases, accounting for 40%, followed by Type Ib, with 141 cases, accounting for 32%. Non-displaced fractures, including Type Ia and Type IIa, totaled 55 cases, representing 12%. The Meyers-McKeever classification had a mean K-value of 0.593 for inter-observer reliability and a mean K-value of 0.896 for intra-observer reliability. However, the Dong classification had a mean K-value of 0.768 for inter-observer reliability and 0.910 for intra-observer reliability.

Conclusion: The CT-based 3D Dong classification is the first proposed 3D CT classification of posterior cruciate ligament avulsion fractures, which helps analyze the type of avulsion fracture and whether it is combined with a tibial plateau fracture from a 3D level. This classification shows higher inter- and intra-observer reliability than the Meyers - McKeever classification and can be used as a complement to the Meyers - McKeever and Schatzker classifications.