New Modification to the Hawkins Classification Scheme Is More Predictive of Osteonecrosis: Commentary on an article by Heather A. Vallier, MD, et al.: “A New Look at the Hawkins Classification for Talar Neck Fractures: Which Features of Injury and Treat

Sheldon S. Lin,Nicholas J. Montemurro

Talar neck fractures are rare injuries that are typically the result of high-velocity traumas. Because of the high rate of osteonecrosis and posttraumatic arthritis associated with talar neck fractures, application of current classification systems for prognostication of the development of talar osteonecrosis and posttraumatic arthritis has been challenging. In a large retrospective review of talar fractures, Halvorson et al. reported the overall rate of posttraumatic talar osteonecrosis in a series of 848 patients to be 33.3% (282 patients). Additional analysis revealed that osteonecrosis occurred in 5.7% (nine) of 159 Hawkins type-I fractures, 18.4% (fifty-eight) of 314 Hawkins type-II fractures, 44.7% (102) of 228 Hawkins type-III fractures, and 12.1% (four) of thirty-three Hawkins type-IV fractures. In another study, Vallier et al. revealed that osteonecrosis occurred in approximately 39% of Hawkins type-II fractures and 64% of Hawkins type-III fractures. Several areas of controversy exist, specifically the wide range of osteonecrosis for Hawkins type-II fractures and potentially the timing of operative fixation.

First, one key observation was the wide range of rates of osteonecrosis for Hawkins type-II fractures, with a rate of 39% reported by Vallier et al. and 18.4% reported by Halvorson et al.. This observation may reflect the vascularity of the talus; knowledge of the blood supply to the talus is critical information in understanding the cause and likelihood of osteonecrosis following talar neck fractures classified according to the Hawkins system. Following a talar neck fracture, the intraosseous branches and artery to the tarsal canal (the blood supply to the inferior surface of the talar body) are ruptured. With this vascularity compromised, the sole vasculature to the talar body is the deltoid branch of the tibial artery that supplies the posteromedial aspect of the talar body. The reported difference in rates of osteonecrosis between Hawkins type-IIA and IIB can be explained by the compromised blood supply that accompanies a type-IIB fracture with a subtalar dislocation. Since the deltoid branch of the tibial artery is less likely to be damaged with a type-IIA fracture with subluxation, there is less chance for vascular compromise and hence lower rates of osteonecrosis. The authors’ modification of the Hawkins classification system by separating fractures with subluxation (type IIA) and with dislocation (type IIB) clarifies the discrepancy in the rates of osteonecrosis. This study demonstrated that zero (0%) of nineteen Hawkins type-IIA fractures developed osteonecrosis in contrast to four (25%) of sixteen Hawkins type-IIB and eleven (41%) of twenty-seven Hawkins type-III fractures that developed osteonecrosis. This modification demonstrates an increased risk of osteonecrosis after talar neck fracture with subtalar dislocation and allows for a more reliable prediction of this adverse event.

Second, previous studies have suggested no association between delayed fracture fixation of talar neck fractures and an increased rate of osteonecrosis. The present study confirms that a delay in definitive fixation has no significant association with the development of osteonecrosis. Forty-six fractures (57%) were treated with definitive fixation with a mean time to fixation of 10.1 hours after injury, and thirty-five fractures were treated with delayed fixation with a mean time to fixation of 10.6 days. The delayed fixation group included ten Hawkins type-IIB and ten Hawkins type-III fractures. Only one (5%) of the twenty fractures in the delayed fixation group developed osteonecrosis. These findings indicate that delaying definitive fixation does not increase the risk of osteonecrosis.

The reader must note several limitations of this study. One shortcoming is that 21% of the original patients were lost to follow-up. The retrospective design and the small number of Hawkins type-II fractures (forty-four) are some additional potential weaknesses of this study. The study was conducted only at a single level-I trauma center between 2001 and 2011. Expansion of the investigation to a multicenter collaborative study would improve the power and validity of the findings. Despite these shortcomings, the present study is the first, to our knowledge, to point out the discrepancy in the Hawkins type-II classification. It also provides further insight into these fractures with the use of the modification to the classification scheme and resolves the controversy with respect to the timing of definitive fixation in the reduction of a talar neck fracture.