**4. Classification**

Some classification systems for calcaneus fractures have poor interobserver reliability, leading to difficulties in describing standardized treatment regimens [21]. Calcaneus fractures can be first classified based on whether they are extraarticular or intraarticular fractures, which account for approximately 25–40% and 60–75% of calcaneus fractures, respectively [22, 23]. Extraarticular calcaneus fractures are classified based on the location of the injury, including the anterior process, the sustentaculum tali, and the calcaneal tuberosity (which can be further classified with the Beavis classification).

The Beavis classification is based on the fracture morphology of the calcaneus tuberosity (**Figure 2**). A type 1 fracture or "Sleeve" fracture is an avulsion of the Achilles tendon with a small shell of cortical bone from the tuberosity. Type 2 or "Beak" fractures have oblique fracture lines that run posteriorly from the most superior portion of the posterior facet. Type 3 or "Infrabursal" fractures are avulsion fractures from the middle of the tuberosity.

Intra-articular calcaneus fractures can be classified with the Essex-Lopresti or the Sanders classification. The Essex-Lopresti classification is based on fracture lines using lateral radiograph images [24]. The primary fracture line runs through the posterior facet. The fracture is classified as tongue-type or depressed based on whether the secondary posteriorly exiting fracture line travels through or inferior to the calcaneal tubercle, respectively. However, the Essex-Lopresti classification has poor interobserver reliability [25].

The Sanders classification system uses coronal computed tomography (CT) scan images to determine the number of articular fragments at the widest point of the posterior facet at the level of the sustentaculum tali (**Figure 3**) [26, 27]. Sanders type I fractures are nondisplaced or have less than 2 mm of displacement, while type II fractures have one fracture line in the posterior facet with displacement. They are further separated into A, B, or C based on the primary fracture line location from lateral to medial. Type III fractures have two fracture lines in the posterior facet and are further separated into AB, AC, or BC based on the two fracture lines. Type IV fractures have three or more fracture lines.

The Crosby-Fitzgibbons system is another classification system based on CT imaging and was developed prior to the Sanders classification [10, 28]. The Crosby-Fitzgibbons classification system divides intra-articular facet fractures into three types. Nondisplaced or minimally displaced fractures are type I. More than 2 mm of

#### **Figure 2.**

*Beavis classification. (a) Illustration of Beavis classification of extra-articular calcaneus fractures. (b) Radiographic example of a type 2 "beak" fracture.*

**Figure 3.** *Sanders classification of intra-articular calcaneus fractures.*
