# Classification and pathoanatomy of posterior malleolus fracture based on posterior malleolus-associated ligaments and ankle stability

## TL;DR

A new classification system for posterior malleolus fractures is proposed based on ligaments and injury mechanisms to improve clinical diagnosis and treatment.

## Contribution

A novel classification system that integrates ligament anatomy, injury mechanisms, and fracture morphology for posterior malleolus fractures.

## Key findings

- The new classification divides posterior malleolus fractures into three types based on ligament involvement and fragment patterns.
- Type II fractures were the most common, with subtypes based on cartilage or die-punch injury presence.
- The proposed system clarifies pathoanatomy and provides better guidance for clinical treatment than previous classifications.

## Abstract

The clinical significance of previous posterior malleolus fracture classifications is limited because they are mainly based on fracture morphology. On the basis of posterior malleolus-associated ligaments and ankle stability, injury mechanism, and fracture morphology, a novel posterior malleolus fracture classification system was proposed to clarify the pathoanatomy of posterior malleolus fracture and guide clinical diagnosis and treatment.

Twenty fresh frozen cadaver specimens of the lower limbs were collected, posterior malleolus-associated ligaments were dissected, and the range of their tibial insertion, average length, and direction were measured. Clinically,we retrospectively analyzed the imaging information of 296 patients with posterior malleolus fractures. Correlating the anatomical measurements of posterior malleolus-associated ligaments of fresh frozen cadaver specimens with the computed tomography(CT) imaging data of posterior malleolus fracture of clinical patients, a clinically practical classification system of posterior malleolus fracture was established. In addition, the novel classification was compared with Haraguci classification and Mason classification.

Posterior malleolus-associated ligaments include the posterior inferior tibiofibular, inferior transverse tibiofibular, and posterior tibiotalar ligaments from the posterolateral to posteromedial tibia. A total of 296 posterior malleolus fractures were divided into three types. Type I posterior malleolus fracture involved only the tibial insertion of the inferior transverse tibiofibular ligament (36 cases, 12.2 %). Type Ⅱ posterior malleolus fracture involved the tibial insertions of the inferior transverse tibiofibular and posterior inferior tibiofibular ligaments and was divided into two subtypes according to whether or not articular cartilage or die-punch injury was present (ⅡA, 150 cases, 50.7 %; ⅡB, 79 cases, 26.7 %). Type Ⅲ posterior malleolus fracture involved all the tibial insertions of the inferior transverse tibiofibular, posterior inferior tibiofibular, and posterior tibiotalar ligaments and included two subtypes according to the fragment number of posterior malleolus fracture (ⅢA, 11 cases, 3.7 %; ⅢB, 20 cases, 6.8 %).

The formation of posterior malleolus fracture stems from the combined effects of external force and internal ligament structure. Correlating posterior malleolus-associated ligaments with the classification of posterior malleolus fracture is of great significance. The proposed classification system considers posterior malleolus-associated ligaments, injury mechanism, and fracture morphology and thus clarifies the pathoanatomy of posterior malleolus fracture and serves as a guide for clinical diagnosis and treatment.

The clinical significance of previous posterior malleolus fracture classifications is limited because they are mainly based on fracture morphology. On the basis of posterior malleolus-associated ligaments and ankle stability, injury mechanism, and fracture morphology, a novel posterior malleolus fracture classification system in our study was proposed. The classification promoted better elucidation of the pathoanatomy of posterior malleolus fracture and guidance for clinical diagnosis and treatment.

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