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Musculoskeletal Imaging |
1 Department of Radiology, Helsinki University Central Hospital,
Töölö Trauma Center, Topeliuksenkatu 5, Helsinki FIN-00029,
Finland.
2 Research Institute of Military Medicine, Mannerheimintie 164, Helsinki
FIN-00300, Finland.
Received December 9, 2003; accepted after revision March 1, 2004.
Address correspondence to S. K. Koskinen
(Seppo.Koskinen{at}hus.fi).
OBJECTIVE. The purpose of our study was to assess MDCT findings and the advantages of MDCT compared with radiography in patients referred to a level 1 trauma center for diagnostic evaluation of acute ankle and foot trauma.
MATERIALS AND METHODS. During a period of 37 months, 388 patients underwent MDCT of the ankle and foot due to an acute trauma. Imaging studies (MDCT and radiography) were retrospectively reevaluated with respect to fracture location, fracture type, and mechanism of injury, and findings from the primary radiographs of the ankle and foot were compared with MDCT findings.
RESULTS. Of the 388 patients, 344 (89%) had one or more fractures in the ankle or foot. A total of 517 fractures were found in all anatomic regions: ankle, calcaneus, talus, midfoot, and forefoot. The three most common occult fractures in the ankle not detected on primary radiography were isolated fractures of the posterior and medial malleolus and Tillaux fractures. The calcaneus was the most commonly fractured bone, and the sensitivity of radiography in the detection of calcaneal fractures was 87%. The sensitivity of radiography in the detection of talar fractures was 78%, whereas it was only 25–33% in the detection of midfoot fractures. A Lisfranc fracture–dislocation was not detected on primary radiography in five (24%) of 21 cases. The three main injury mechanisms were falling from a height (164 patients [48%]), a simple fall (68 patients [20%]), and a traffic accident (47 patients [14%]).
CONCLUSION. In patients with injuries from high-energy polytrauma and in those with complex ankle and foot fractures, the sensitivity of radiography is only moderate to poor; in these cases, MDCT is recommended as the primary imaging technique.
Conventional radiography has had and still has an essential and dominant role in the diagnostic evaluation of patients with acute ankle and foot trauma. In patients with complex ankle and foot fractures, however, CT is a commonly used imaging technique after radiography. The prevalence of complex injuries of the ankle and foot seems to be increasing as a result of the increased use of automobile safety devices, such as seat belts and air bags, that decrease mortality and protect the trunk but not necessarily the lower extremities [1].
As a result of technical breakthroughs, MDCT is faster and has better temporal, spatial, and contrast resolution than conventional helical CT [2]. Also, 2D reformats (multiplanar reconstructions) and 3D surface renderings are of excellent quality; and because the image processing is fast, these images can be made almost instantly. The purpose of our study was to assess the MDCT findings and the advantages of MDCT compared with radiography in patients referred to a level 1 trauma center for evaluation of acute ankle and foot trauma.
Materials and Methods
This retrospective study took place at the Töölö Trauma Center in Helsinki, Finland. It serves as the only level 1 trauma center for a population of 1.4 million people and is the leading level 1 trauma center in Finland. In addition, some of the most difficult cases of orthopedic and neurosurgical trauma are referred to the Töölö Trauma Center from all over the country. Pediatric patients, those under the age of 16 years, are primarily taken to Children's Hospital and therefore were not included in the present study.
Using the PACS at our hospital, we retrieved all emergency department CT requests dating from the installation of a 4-MDCT scanner in August 2000 to the end of August 2003. A total of 7,139 MDCT examinations were performed during this 37-month period at the request of emergency department physicians. Patients with an acute ankle and foot injury and who underwent ankle and foot MDCT in the primary phase were included in the study. The ankle and foot MDCT examinations were requested by emergency department physicians mainly to reveal complex fracture anatomy or to rule out a fracture.
Of these patients, 388 patients (282 males and 106 females; age range, 16–89 years; mean age, 40 years) met the inclusion criteria. All patients underwent CT on a 4-MDCT scanner (LightSpeed QX/i, GE Healthcare). Routine MDCT examinations of the ankle and foot were performed as follows: 4 x 1.25 mm collimation, 0.625-mm interval, and 3.75-mm table speed. Routine 2D reformats were performed in standard coronal and sagittal planes with a slice thickness of 1.0 mm and a reconstruction increment of 1.0 mm.
In this study, the diagnosis of acute traumatic ankle or foot fracture was based on MDCT, which was regarded as the gold standard. Two radiologists experienced in musculoskeletal imaging reevaluated retrospectively and by consensus the imaging studies (MDCT and radiography) by fracture location, fracture type, and injury mechanism. Primary radiographs of the ankle (anteroposterior, 20° internal oblique [mortise], and lateral views) and of the foot (anteroposterior, oblique, and lateral views), when available, were reevaluated by consensus and were then compared with MDCT images.
Results
Of the 388 patients, 344 (89%) had one or more fractures in ankle or foot. A total of 517 fractures were found in all five anatomic regions: ankle, calcaneus, talus, midfoot (navicular, cuboid, or cuneiform bones), and forefoot (metatarsal bones). The number of the patients and number of fractures according to anatomic location are shown in Table 1. Nine patients (3%) had a talocrural fracture–dislocation, and 12 patients (3%) had luxation of Chopart's joint (one case was bilateral). Twenty-four patients (7%) had a Lisfranc fracture–dislocation and two of these patients also had a bilateral tarsometatarsal fracture–dislocation.
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Primary radiographs were available for 296 patients (86%) with fractures. The number of the fractures detected on MDCT versus on primary radiography is shown according to location in Table 2. The three most common occult fractures in the ankle not detected on primary radiography were the isolated fractures of the posterior and medial malleolus and the lateral margin of the distal tibia (Tillaux fracture), for which the sensitivity of primary radiography was 50–72% (Figs. 1A, 1B, 1C, 1D, 1E, 1F and 2A, 2B, 2C, 2D). The calcaneus was the most commonly fractured bone in the present study, and the overall sensitivity of primary radiography compared with MDCT was 87% in this fracture group (Table 2). Especially in cases of complex intraarticular fracture patterns, MDCT with coronal and sagittal multiplanar reconstructions revealed the extent of the fractures and the position of the dislocated posterior calcaneal facet better than conventional radiography (Figs. 3A, 3B, 3C, 3D, 3E, 3F, 3G, and 3H).
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The overall sensitivity of conventional radiography for the detection of talar fractures was 78% compared with MDCT (Table 2). MDCT with multiplanar reconstructions was most helpful in detecting isolated fractures of the talar trochlea because these fractures were shown on conventional radiographs in only 34 (68%) of 50 cases. Eight talar fractures (11%) were associated with a subtalar joint dislocation, and the intraarticular fracture was detected in seven of eight cases on primary radiography. The total number of luxations of Chopart's joint was 13 (3%), and five cases were associated with navicular intraarticular fracture; no fractures of the corresponding talar joint facet were seen in the patients with Chopart's joint luxation. Only one of four intraarticular navicular bone fractures was shown on conventional radiographs. Therefore, intraarticular fractures in subtalar or talonavicular dislocations were seen on conventional radiography in eight of 12 cases.
In the detection of midfoot fractures, the sensitivity of primary radiography was 24–33% compared with MDCT (Table 2). The total number of Lisfranc fracture–dislocations was 26 (5%), and an occult Lisfranc fracture–dislocation was detected in five cases (24%) on MDCT because primary radiographs were available in 21 cases. MDCT with multiplanar reconstructions provided better visualization of the complex fracture anatomy and of even minimal joint malalignment of the Lisfranc joint without superimposed structures. The extent of the fractures and of the dislocated joint facets of all Lisfranc fracture–dislocations was better evaluated on multiplanar reconstructions than on radiographs (Figs. 4A, 4B, 4C, and 4D).
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In our patient population, the three main injury mechanisms were falling from a height (164 patients [48%]), a simple fall (68 patients [20%]), and a traffic accident (47 patients [14%]). Eighty-eight patients (26%) also had serious injuries in other parts of the body. The three most common injuries elsewhere were thoracic fractures with hemo- and pneumothorax and pulmonary contusions (29 patients [33%] patients), multiple pelvic fractures (24 patients [27%]), and lumbar vertebral fractures (20 patients [23%]). In these patients with polytrauma, the injury mechanism was associated more frequently with falling from a height or traffic accidents. Fractures in 223 patients (65%) were surgically managed, and ankle fractures were the most common type of fracture to be surgically treated. A fall from a height was the main single injury mechanism in all fracture groups, especially for the talus, calcaneus, and midfoot fractures (Table 3).
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Ninety-nine patients (29%) had multiple fractures of the ankle or foot. The four most common combinations of multiple fractures were forefoot and midfoot fractures in 21 patients (21%), ankle and calcaneus fractures in 12 patients (12%), ankle and talus fractures in 11 patients (11%), and talus and calcaneus fractures in 10 patients (10%).
Forty-four patients (11%) had negative MDCT findings. In 29 patients (7%) a fracture was suspected on the primary radiograph, but these cases were proven to be false-positive on the basis of MDCT findings. A suspected fracture of the talus was the most common false-positive diagnosis on primary radiography in 12 patients (41%). Fifteen patients (4%) with no fractures in the ankle or foot underwent MDCT because clinical and primary radiographic signs were inconclusive and the surgeon wanted to rule out an occult fracture.
Discussion
The ankle is the most commonly injured joint in the body, and ankle fractures are the most common types of fractures treated by orthopedic surgeons [3]. An occult posterior malleolus fracture can be potentially harmful and can cause complications if not detected and accurately managed because internal fixation of the posterior malleolus is recommended if the reduced fragment constitutes more than one fourth to one third of the tibial articular surface [1]. Obtaining an internal oblique view in addition to the anteroposterior and lateral projections increases the sensitivity of conventional radiography in the detection of ankle fractures [4], but in patients with polytrauma and in those with severe comminuted ankle fractures, the appropriate positioning of the ankle is difficult. On MDCT, the position of the ankle is not crucial because of the high quality of the reformats. The patterns of articular fracture in the distal part of the tibia, especially in comminuted pilon fractures, can be difficult to manage and therefore MDCT scans with multiplanar reconstructions enhance the preoperative assessment of the fracture and operative decision making.
The calcaneus is the most commonly fractured foot bone [5]. Calcaneal fractures are the result of high-energy trauma, usually due to a fall from a height or to a motor vehicle accident [6], which was also seen in the present study. Nonoperative treatment is best reserved for nondisplaced calcaneal fractures; however, for patients who have displaced intraarticular fracture fragments, nonoperative treatment offers little chance of a return to normal function because a calcaneal malunion will develop [6–8]. In intraarticular calcaneal fractures, the degree of the depression of the posterior calcaneal facet may often be underestimated on lateral radiographs and also on coronal CT images [9, 10]. Multiplanar reconstructions in sagittal and coronal planes show the exact position of the posterior facet and joint malalignment without superimposed structures, thus helping decision making between operative and nonoperative treatments.
Fractures of the talus, constituting 3–6% of all foot fractures according to the literature [11, 12], are relatively rare. In the present study, talar fractures constituted 14% of all fractures. This difference is probably because our study population was composed of patients being treated at a level 1 trauma center for injuries caused by high-energy trauma and because patients with more simple foot injuries are treated on the basis of conventional radiographs and do not undergo MDCT. Subtalar joint dislocation is not a common injury [13], but this finding was seen in 11% of all talus fractures in our study; again, this unexpected finding is best explained by the majority of high-energy trauma patients in this study. Subtalar joint dislocations with associated intraarticular fractures involving the subtalar or talonavicular joints can lead to significant subtalar joint arthrosis [14]. The overall sensitivity of conventional radiography in the detection of talar fractures is only moderate, and making the diagnosis of associated intraarticular fractures of the subtalar or talonavicular joint with a subtalar joint dislocation is even more difficult on conventional radiographs [15], as was also seen in our study. The presence of an intraarticular fracture worsens the prognosis [13], and MDCT with multiplanar reconstructions is a recommended complementary examination to reveal a possible occult intraarticular fracture of the talus if subtalar joint dislocation or subluxation is suspected.
In the detection of midfoot fractures, the sensitivity of primary radiography was weak compared with MDCT. These fractures may be potentially harmful and can cause complications if not detected and accurately managed. In the Lisfranc joint, the minimal tarsometatarsal malalignment and fracture lines are difficult to detect on conventional radiographs [16–20], and as many as 20% of Lisfranc joint injuries are estimated to be missed on primary anteroposterior and oblique radiographs [21–23]. In the present study, the percentage of radiographs with false-negative findings was slightly higher. This difference may be because of the patient population: weight-bearing images cannot usually be obtained in patients with polytrauma, and appropriate positioning is also difficult in patients with severe ankle and foot trauma. Operative treatment is usually needed in patients with a Lisfranc fracture–dislocation to achieve anatomic reduction and fixation. Multiplanar reconstructions reveal the extent of the fractures and even minimally dislocated joint facets in these complex fractures better than radiographs, thus helping surgical planning.
CT is a commonly used imaging technique after radiography in the setting of ankle and foot fracture. Compared with conventional helical CT, MDCT is faster and has fewer motion artifacts. It offers reduced partial volume effects, decreased image noise, high-quality multiplanar reconstructions, and isotropic viewing, all of which increase its diagnostic power and benefit patients who present to the emergency department with trauma [2, 24]. The position of the ankle or foot is not crucial because the reformats are of excellent quality. The high-quality multiplanar reconstruction capability is especially useful in analyzing complex ankle and foot fractures. Therefore, in our hospital, sagittal and coronal reformats are routinely included; CT technologists make these standard multiplanar reconstructions; and radiologists, if needed, make the additional multiplanar reconstructions. The average effective radiation dose for an MDCT examination of the extremities, such as ankle and foot, is 1 mSv [25], which of course depends on the size and length of the body part examined and scanning parameters (slice thickness, kilovoltage, current). The effective dose for radiography of the extremities is approximately 0.01 mSv [26]. The radiation dose is higher for the MDCT examination than for the conventional radiography examination, but MDCT examination of the extremities can still be considered a low-dose examination [26].
The sensitivity of conventional radiography is only moderate in the detection of serious ankle and foot injuries. MDCT is an accurate and reliable imaging technique in evaluating patients with ankle and foot traumas. Multiplanar reconstructions are helpful in disclosing fracture patterns, particularly in complex fractures of the ankle and foot, where they enable comprehensive evaluation of fracture components and also reveal occult fractures. These fractures may be potentially harmful and can cause complications if not detected and accurately managed. The degree of dislocated joint facets is better evaluated on MDCT with multiplanar reconstructions than on radiography. Patients known to have multiple injuries from high-energy trauma usually have multiple fractures; therefore, the whole ankle and foot should be scanned if an MDCT examination is planned. As shown in this study, MDCT reveals occult fractures and depicts the exact fracture anatomy in ankle and foot fractures, such as tibial pilon and complex calcaneal fractures.
In conclusion, radiography remains the primary imaging technique in evaluating patients with ankle and foot trauma; however, in patients with multiple injuries from high-energy trauma and in patients with complex fracture patterns the sensitivity of conventional radiography is only moderate to poor. In these cases, MDCT of the whole ankle and foot is recommended as the primary imaging technique.
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