Despite the advent of more advanced imaging modalities, radiographs still play a critical role in the evaluation of osteonecrosis of the talus [2]. The body’s response to osteonecrosis is an attempt at repair by means of reossification, revascularization, and resorption of necrotic bone [19]. At initial radiography, necrotic bone and the surrounding viable bone are equal in opacity, and early stages can be missed [20]. As time passes and hyperemia results, healthy bone is resorbed and subsequently becomes osteopenic [20]. Conversely, the lack of blood supply in necrotic bone prevents its resorption, making necrotic bone appear more radiopaque than the surrounding osteopenic bone. At that point, radiographic evidence of osteonecrosis becomes apparent. The opacity of necrotic bone continues to increase as reossification occurs and new bone is laid down over necrotic trabeculae. This process accounts for the typical sclerotic image seen in osteonecrosis of the talus. In addition to reossification, revascularization and resorption also tend to occur around necrotic bone. When these processes occur, a radiolucent rim becomes apparent around the area of osteonecrosis [19, 21]. Radiographs are especially useful following open reduction and internal fixation of displaced talar neck and body fractures [2]. Hawkins’ sign is characterized by subchondral osteopenia on anteroposterior or mortise radiographs [3]. Typically, it is present at 6–8 weeks and results from the resorption of subchondral bone in the setting of disuse and a sufficient vascular supply [3]. Canale and Kelly evaluated the reliability of Hawkins’ sign at 12 weeks postoperatively in 49 patients [4]. They found that 20 of 26 (77 %) fractures that did not have subchondral osteopenia developed osteonecrosis. However, one of 23 cases that had a positive Hawkins’ sign went on to osteonecrosis. Thus Hawkins’ sign is a reliable indicator of talar viability and its presence serves as an early negative predictor of osteonecrosis [2–4]. The absence of Hawkins’ sign, however, does not confirm osteonecrosis, because it has greater sensitivity than specificity [2–4].

MR imaging is the most sensitive technique for detecting osteonecrosis of the talus, especially in the early stages [20]. In addition, MR imaging is considered more anatomically detailed and accurate than radiographs and scintigraphy in its ability to identify the extent of talar body involvement [22]. On MR imaging, osteonecrosis of the talus typically is characterized by low signal on T1-weighted images [2]. On T2-weighted images, osteonecrosis produces a mixed and variable appearance that depends on the contents of the avascular region [2]. However, MR imaging non-contrast enhanced is a problem due to the confusing picture of bone edema and ONT having a similar appearance [23]. We recommend MR imaging with contrast such as gadolinium enhancement for accurate diagnosis on early stage of ONT and should be combined with the clinical findings.

Computer tomography (CT) scans also reveal characteristic osteonecrosis of the talus patterns and can be used to confirm radiographic findings. The CT arthrogram is a especially helpful method to evaluate the volume and location of the remaining dead bone and associated cartilage damage [23]. Coronal CT of the talus is required for viewing the articular surface of the talar dome to rule out subtle depression, collapse, and fragmentation, especially at preoperative assessment [20] (Fig. 56.2).

The presence of osteonecrosis of the talus before collapse is initially treated nonoperatively. The nonoperative treatment options include applying a short-leg cast, ankle-foot orthosis with analgesics, and no weight bearing [25]. Some previous studies recommend extended non-weight bearing [3, 26]. Others have recommended a patella tendon bearing brace until reconstitution of the talar body is complete [27–29]. However, because the creeping substitution of the talar body can require 36 months to occur, patient compliance is rarely possible for 36 months [1, 30]. Penny et al. [31] reported that weight bearing on sclerotic and osteonecrosis of the talus poses no danger for talar dome collapse and found no relation between poor results with osteonecrosis of the talus and time of non-weight bearing. Therefore, the current consensus is to permit weight bearing as soon as tolerable.

Several treatment options are available for osteonecrosis of the talus. However, surgical treatment options for symptomatic osteonecrosis of the talus are limited. These are core decompression, allograft reconstruction, vascularized autograft reconstruction for early precollapse stage, and arthrodesis and arthroplasty for late postcollapse stage [24, 25, 32–38].