The pilon fracture has two classifications that are commonly used. The first classification is the Ruedi-Allgower Classification, which is an old classification, and the second is known as the AO/OTA Classification.
The Ruedi-Allgower Classification is separated into three types. Type I fractures are cleavage fractures with no significant joint incongruity and no displacement of the fractured fragments. Type II fractures have a significant articular incongruity with minimal metaphyseal comminution or impaction. Type III fractures have significant articular comminution and a metaphyseal impaction; this is a very bad injury.
You will find three types of AO/OTA classifications and they are as follows: Extra-articular, partial articular, and complete articular. The extra-articular fractures are further broken down into simple (A1), metaphyseal wedge (A2), and metaphyseal complex fractures (A3). All of these extra-articular fractures are named “A”, followed by a number based on the complexity of the fracture. Partial-articular fractures are classified further with the letter “B” and are identified as Pure Split (B1), Split Depression (B2), and Multi-fragmentary depression (B3).
Split Depression fractures are a supination/adduction fracture of the ankle which is identified as a vertical fracture of the medial malleolus. The anteromedial portion of the plafond may also be impacted. The impaction or depression unique to this fracture is commonly missed, making this fracture a classic question on orthopaedic examinations. If the surgeon misses the impaction fracture after fracture fixation, they will need to revise the fixation and be sure to elevate the impaction or depression; additionally, they will need to restore the joint congruity before fixing the fracture. The surgeon will need to fix the fracture with a plate or screws. If screws are used, they have to be parallel to the joint in order to compress the fracture. If a plate is used, it should be an anti-glide plate.
The “C” fractures are Complete Articular fractures and have complete joint involvement. The Complete Articular fractures are broken down into Articular Simple/Metaphysis Simple (C1), Articular Simple Metaphysis Multi-fragmentary (C2), and Articular Multi-fragmentary/Metaphysis Multi-fragmentary (C3). C3 fractures are a very difficult fracture and probably has the worst prognosis.
Classically, there is a typical pilon fracture fragment. Usually there are three main joint fragments. The Three fragments are the:
- Medial Malleolus
- Attached to the deltoid ligament
- Anterolateral Fragment
- Chaput Fragment- attached to the anterior inferior tibiofibular ligament
- Volkmann Fragment
- Posterolateral fragment attached to the posterior inferior tibiofibular ligament
When the fibula is intact, the lateral collateral ligament of the ankle may rupture (fibula is intact in 20% of the cases).