Minor fractures
- Avulsion fractures of the Achilles tendon insertion - most are simple avulsion fractures. Neuropathic fractures can occur at this site (Brodsky type 3B)
- Fracture of the tuberosity - usually direct injury
- Fracture of the anterior process - usually caused by an inversion injury and may be missed in what was thought to be an ankle ligmament injury. Always consider this injury in the differential diagnosis of the "sprained" ankle that fails to settle. It is usually seen on an oblique radiograph of the foot but may need an isotope bone scan or CT for diagnosis. Petrover et al (2007) found that 60% had calcaneonavicular coalitions and 69% bifurcate ligament sprains.
Achilles tendon insertion avulsion fracture
Tuberosity fracture
Anterior process fracture
Body fractures
Fractures of the body are divided into those which are extra-articular and those which are intra-articular, mainly into the subtalar joint.
Early classifications were based on plain radiography. The best known is that of Essex-Lopresti, who recognised peripheral and extra-articular injuries, and divided intra-articular injuries into:
joint-depression type, in which the primary fracture line exited the bone close to the subtalar joint
tongue-type, in which the primary fracture line exited the bone posteriorly
Review the pathomechanics of these fracture types
This classification was related to his percutaneous reduction technique. As minimally invasive fixation has attracted more interest in the last few years, it is once again important to know the Essex-Lopresti classification. The minimally invasive techniques for reduction are different for tongue-type and joint depression fractures.
Modern classifications are based on CT imaging of the posterior subtalar articular facet. Crosby and Fitzgibbons (1993) divided 30 intra-articular fractures into undisplaced, displaced but non-comminuted, and comminuted, and showed that severity corelated with outcome and response to surgery.
The main CT classification is that of Sanders (1993). The main axis of classification is into
- type-1 fractures, in which the articular fragments are displaced less than 2mm relative to one another
- type-2 fractures, in which there are two articular fragments which are displaced at least 2mm relative to one another
- type-3 fractures, in which there are three articular fragments which are displaced at least 2mm relative to one another
- type-4 fractures, in which there are four or more articular fragments which are displaced at least 2mm relative to one another
The type-2 and 3 fractures are subdivided on the position of the articular fracture lines, producing types 2A, 2B and 2C, and types 3AB, 3AC and 3BC.
The basis of the Sanders classification.The groups are denoted by the number of main fragments and the approximate main fracture lines as marked
A two-part fracture with the main fracture line through the mid-part of the joint - type 2B
A three-part fracture with the main fracture lines lateral and central - type 3AB
A four-part fracture with fracture lines lateral, medial and central - type 4ABC
The main typings have been shown to influence prognosis and surgical complexity (Sanders 1993), and overall benefit from surgery (Buckley et al 2002). Rubino (2009) found that the Sanders and Regazzoni (AO) calssifications were best corelated with typical foot and ankle outcome measures.
Furey (2003) studied interobserver variability using the Sanders classification and found moderate agreement with a weighted kappa value of 0.48 for the main classes and 0.56 including the subclasses. De Souza et al (2004) found 37/150 calcaneal fractures that could not be classified according to Sanders and described additional types and appropriate surgical strategies. Schepers (2009) also found kappa values of around 0.5 for the Sanders, Essex-Lopresti and Crosby/Fitzgibbons classification when these were applied by trauma surgeons, but less for radiologists. Sayed-Noor (2011) and Howells (2013) produced even lower values for agreement, suggesting that a critical revision of existing classification systems is required.