Characteristics and proposed classification system of posterior pilon fractures

Abstract

Posterior pilon fractures involve the medial malleolus (MM). Our purpose was to define the characteristics of posterior pilon fractures, and propose a classification system based on fracture morphology and type of management.The records of patients with posterior pilon fractures treated from 2011 to 2015 were retrospectively reviewed. The injury mechanism, fracture morphology, surgical approach, and follow-up results were reviewed and analyzed. This study was approved by the Institutional Review Board of PLA Army General Hospital.Thirty-six patients, 18 males and 18 females (mean age: 48.9 years) were included in the study. Four characteristics were used to define posterior pilon fractures. A simple posterolateral approach or a combined posterolateral and posteromedial approach was used for reduction and fixation in all patients. The mean follow-up time was 28.2 months, and at the end of follow-up, the mean American Orthopedic Foot and Ankle Society Score (AOFAS) was 82.5 points (range: 35-100 points). Based on injury mechanism and fracture morphology, we classified posterior pilon fractures into 3 types that suggest the optimal surgical approach: type I, a single complete fracture fragment; type II, a posterior malleolus fracture with 2 subtypes; type III, a posterior malleolus fracture associated with complete MM fracture with 2 subtypes.The proposed classification system based on injury mechanism and fracture morphology can guide the surgical approach to maximize outcomes.

Figure 1

Schematic illustration of the Army General Hospital classification. (A) Type I fracture: the posterior malleolus is a single complete bone fragment. (B) Type IIa fracture: the posterior malleolus fracture is divided into 2 parts, posteromedial and PL. (C) Type IIb fracture: the posterior malleolus fracture is a comminuted fracture. (D) Type IIIa fracture: the fracture line of the posterior malleolus fracture involves the AC of the MM, the MM fracture is a complete fracture, but the AC and PC are not separated. (E) Type IIIb fracture: the posterior malleolus fracture line involves the intercollicular groove, the AC fracture is an avulsion fracture associated with separation of the AC and PC. AC = anterior colliculus, MM = medial malleolus, PC = posterior colliculus.

Figure 2

Surgical approaches for posterior pilon fractures. (A) Posterolateral incision. (B) Combined posterolateral and posteromedial incision. (C) Extended posteromedial incision.

Figure 3

A 45-year-old male had a posterior pilon fracture due to a fall. It was a type I fracture, and the posterior malleolus was a single complete bone fragment. (A) CT axial scan showed that the curved fracture line of the posterior malleolus involves the MM. (B) The CT reconstruction showed that the posterior malleolus fracture was associated with posterior dislocation of the ankle joint. (C) Three-dimensional (3D) CT reconstruction showed that the posterior malleolus is a single complete bone fracture, and the fracture line involves the MM. (D) Reduction and fixation of the lateral malleolus and MM were carried out via the posterolateral approach. This postoperative x-ray image shows reduction of the posterior malleolus fracture with a smooth articular surface. (E) This postoperative lateral x-ray image shows anterior-to-posterior screw fixation following reduction of the posterior malleolus fracture. CT = computed tomography, MM = medial malleolus.

Figure 4

A 43-year-old female had a posterior pilon fracture due to a car accident. It was a type IIa fracture; the posterior malleolus was split into 2 parts, PM and PL. (A) Axial CT showed the posterior malleolus was divided into 2 parts. (B) 3D CT reconstruction showed the posterior malleolus was divided into 2 parts, and the posteromedial fracture involved the MM. (C) Reduction and buttress plate fixation were carried out via a combined posteromedial and posterolateral approach. Postoperative anteroposterior x-ray images showed reduction of the posterior malleolus fracture, with a smooth articular surface. (D) Anteroposterior x-ray images taken 12 months after surgery showed bony healing of the posterior malleolus and lateral malleolus fractures with a smooth articular surface. MM = medial malleolus, PL = posterolateral fragment.

Figure 5

A 62-year-old female had a posterior pilon fracture due to a car accident. It was a type IIb fracture (a comminuted fracture). (A) Axial CT showed the comminuted posterior malleolus fracture. The posteromedial fracture line involved the MM. (B) CT 3D reconstruction showed the comminuted posterior malleolus fracture. The arrow indicates several fracture fragments of the posterior malleolus. (C) Reduction and buttress plate fixation were carried out via a combined posteromedial and posterolateral approach. The postoperative anteroposterior x-ray image showed reduction of the posterior malleolus fracture with a smooth articular surface. (D) Anteroposterior x-ray images taken 12 months after surgery showed bony healing of the posterior malleolus and lateral malleolus fractures, with a smooth articular surface. MM = medial malleolus.

Figure 6

A 22-year-old male had a posterior pilon fracture due to a fall. It was a type IIIa fracture; the posterior malleolus fracture involved the AC of the MM, the MM fracture was a complete fracture, but the AC and PC were not separated. (A) Axial CT showed that the posterior malleolus fracture involved the AC of the MM, the fracture line was L-shaped, and there was a depressed die-punch fragment between the 2 fracture ends. (B). CT 3D reconstruction showed that the posterior malleolus fracture involved the AC of the MM. (C) Reduction and buttress plate fixation were carried out via a combined posterolateral and extended posteromedial approach. Postoperative anteroposterior x-ray images showed reduction of the posterior malleolus fracture with a smooth articular surface. (D) Twelve months after surgery, the affected ankle showed satisfactory functional recovery. AC = anterior colliculus, MM = medial malleolus, PC = posterior colliculus.

Figure 7

A 32-year-old female had a posterior pilon fracture due to falling. It was a type IIIb fracture; the posterior malleolus fracture line involved the intercollicular groove, there was an avulsion fracture of the AC, and the AC was separated from the PC. (A) The preoperative anteroposterior X-ray image and CT axial image showed fracture dislocation of the ankle joint and transverse fracture of the posterior malleolus, the posteromedial fracture involved the PC of the MM, and there was an MM fracture. (B) CT 3D reconstruction showed that the posterior malleolus fracture involved the PC (the black arrow indicates the avulsion fracture of the AC). (C) Reduction and buttress plate fixation were carried out via a combined posterolateral and extended posteromedial approach. The MM was fixed with a K-wire. Postoperative anteroposterior X-ray image showed reduction of the posterior malleolus fracture with a smooth articular surface. (D) Anteroposterior X-ray image taken 12 months after surgery showed bony healing of the posterior malleolus and lateral malleolus fractures with a smooth articular surface. AC = anterior colliculus, MM = medial malleolus, PC = posterior colliculus.