Avulsion Fracture of the Calcaneal Tuberosity: Classification and Its Characteristics

BACKGROUND: Not much is known regarding avulsion fractures of the calcaneal tuberosity. We propose a modified classification scheme that presents the four types of calcaneal avulsion fracture as described by surgical and magnetic resonance imaging (MRI) findings, and evaluation of their specific features. METHODS: Out of 764 cases of calcaneal fractures, we examined 20 cases (2.6%) that involved the tuberosity of the calcaneus. Each case was classified depending on the avulsed fracture patterns as follows; type I is a 'simple extra-articular avulsion' fracture, type II is the 'beak' fracture, type III is an infrabursal avulsion fracture from the middle third of the posterior tuberosity, and finally in type IV there is the 'beak', but a small triangular fragment is separated from the upper border of the tuberosity. We examined the features of each avulsed type according to several criteria including patient age, gender, anatomical variances of the Achilles tendon, the fibers involved and the mechanism of injury. RESULTS: The type I fracture (8/20 cases) was the most common and likely to occur in elderly women. However, in other types, they were more common in relatively younger male patients. Type I were usually caused due to an accidental trip causing a fall by the patient. However, the dominant cause of type II (5/20 cases) fractures a direct blow or hit directly to the bone. Type III (4/20 cases) and IV (3/20 cases) fractures were likely to occur due to falling. All fibers within the Achilles tendon are involved in both type I and II fractures. However, only the superficial fibers are involved in type III fractures, whereas the deep fibers are involved in type IV fractures. CONCLUSIONS: The avulsion patterns of the calcaneal tuberosity fractures are the result of several factors including the bony density level, the mechanism of injury and the fibers of the Achilles tendon that transmit the force. Accurate diagnosis of type III and IV is dependant on MRI technology to confirm the specific location of the injury and provide proper patient treatment therapeutics.