Section: Canada Category: Imaging Radiology

Radiographic Pitfalls In Lower Extremity Trauma

Marlena Jbara, MD

Marlena Jbara, MD discusses common radiographic pitfalls in lower extremity trauma. Dr Jbara also discusses strategies for dealing with the common radiographic pitfalls in lower extremity trauma.

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Goals and Objectives
  1. Explain common radiographic pitfalls in lower extremity trauma
  2. Propose strategies for dealing with them
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  • CPME (Credits: 0.75)

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  • Author
  • Marlena Jbara, MD

    Assistant Professor Radiology
    SIUH Northwell Health
    Staten Island, NY

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  • Lecture Transcript
  • TAPE STARTS – [00:00]

    Marlena Jbara: Hi, my name is Marlena Jbara and I'm going to discuss radiographic pitfalls in lower extremity trauma. Welcome. I or related party have no financial relationships to disclose. Objectives: We are going to examine common radiographic pitfalls in lower extremity trauma and discuss strategies for dealing with them. Insufficient views, our first pitfall. So many fractures are visible only on a single view and if other views are not obtained, you are going to get false negatives. In our institution, pretty much it's standard that for any joints that will be three views and for any long bone that's at least two views, if there is an exceptionally long tibia fibula or femur, it may require several cassettes up to four views. So at the University of Washington, one of the major trauma centers in our country, there is published guidelines for the body part of hip that you would receive an anteroposterior and cross-table or frog-leg lateral of the affected hip. For the femur, you would take an anteroposterior and lateral. For the knee, anteroposterior, lateral and both obliques. For the tibia and fibula, an anteroposterior and lateral. For the ankle, again three views, the anteroposterior, oblique or ankle mortis view and lateral. For the foot, the anteroposterior, oblique and lateral. And lastly for the calcaneus, a lateral and axial or Harris Beath view would be indicated.


    Insufficient views: In this example, a patella fracture may not be evident unless an axial view is obtained. So in this case, you can see the multiple avulsion fragments below the medial patella facet not visible on either the AP or lateral projections. Insufficient views, lack of weightbearing. So lack of weightbearing can lead to false negative results in dealing with Lisfranc or Chopart joint injuries. So areas of bony structures where there is multiple overlapping shadows, it may be difficult to ascertain whether there is a fracture. Stress views may be needed to show injury to the ankle mortise or syndesmotic diastasis. So if the x-rays are initially negative but there is a high clinical suspicion, you may want to go on to advanced imaging such as CT or MRI. MRI is better at identifying soft tissue injuries that may have clinical importance and may guide treatment one way or the other. Improperly positioned or technically imperfect radiographs is another pitfall. So having insufficient tube current will lead to an underexposed radiographs with just less information available. The monitors are going to present to the image with expected gray scale, contrast and brightness. You are not going to know the difference. So false negative can result. For proper positioning and exposure, it's crucial to maintain standards for accurate image interpretation. In this example of the same patient obtained with two different techniques, one can see in the normal technique that you have fractures to the second and third mid metatarsal diaphysis, which cannot be seen on this under-penetrated examination with improper tube angulation.


    Notice the lack of soft tissue differentiation and the whole gray scale being just smudged out and less contrasty. In addition, along the lines of improperly positioned or technically imperfect radiographs, image compression and use of substandard handheld displays may impeded your ability to see something. Clearly, the viewing monitor of an iPhone is not as good as one of the barcode dedicated DICOM readers. And in addition, bright light, glare and reflection reduce diagnostic interpretation and there are usually advanced imaging tools that are built in to the PACS system which allow us to manipulate the image, which has greater sensitivities and specificities to manipulate the image to bring out the pathology. For nondisplaced fractures, they may be clinically apparent but x-rays remain negative even when the x-ray is properly positioned and technically perfect. So fracture detection actually requires a minimal degree of displacement. And if you have a high clinical index suspicion for fracture, someone is not walking, something very swollen, you can always go on to have additional imaging to corroborate your suspicion or be able to treat conservatively and confidently. For nondisplaced fractures, when imaging effect will affect the patient management, a thorough evaluation should be ascertained.


    For example, a classic area is in the osteoporotic hip. This is a disease that has surgical management and in the presence of diffuse bone demineralization, a nondisplaced fracture may be less visible on x-ray. A negative x-ray with a high pretest probability. For example, an elderly patient with hip pain status post fall. You want to liberally go on to CT or even better MRI for a superior soft tissue contrast. In this example on the left where you have osteopenic bones, there is no fracture seen. And in this example on the right, you have a femoral neck fracture with bone marrow edema and hypointense T1 signal changes from the subcapital femoral to mid cervical femoral neck. And this is an example of how little you can see as possible to see on an x-ray and still have the presence of a fracture. As for nondisplaced fractures, the American College of Radiology currently recommends MRI over CAT scan for middle aged elderly patient with negative x-rays. There is a mixed opinion in the literature regarding CT versus MRI. An MRI is better for detecting bone marrow edema. CT is better for polytrauma screening and sonogram may be useful in the future to evaluate extension of fifth metatarsal fracture imaging. It shows promise but initial focus examination may miss other injuries. Moving on to common location of errors, one important emergency room radiology study found that 51.4% of missed fractures involve the ankle or foot. In a different study, commonly missed lower extremity fractures involve the following regions in decreasing order. Foot, knee, followed by hip and then ankle.


    Providing a systematic approach is going to be important in the use of high-risk areas to guide image interpretation. So understanding the x-ray anatomy is essential. And moving through the bony structures on this image on the left, we can go from medial to lateral and looking at the medial malleolus, the tibial plafond, the talar dome, the lateral malleolus. We can go down the line to the lateral talar process, go across the medial talar process, go to the extensor digitorum brevis attachment at the anterolateral calcaneus. Looking on the oblique image, you get a sense of the lateral talar process and the medial malleolar. You can see this even the fibers of the deltoid ligament. On the lateral, you can see the dorsal talonavicular articulation and it's always important to evaluate the anterior superior calcaneal process. You can also evaluate subtalar joint anatomy moving back along the line to evaluate the syndesmosis. Looking at the lateral tibiofibular clear space going 1 cm from the tibial plafond superior to the distal fibula and assessing the lateral tib-fib clear space for syndesmotic injury. Common location of errors.

    If an ankle is injured, we can assess the proximal fibula looking for maisonneuve fracture, pronation, external rotation injuries and associated distal tibia fibular syndesmotic disruption and proximal fibular fractures. As for calcaneal fractures, there is also association with the lumbar fractures. Posterior malleolar fractures, we can think about association with the distal tibial spiral fracture. It may be a part of trimalleolar fracture complex. So knowing your mechanism of injury and position of foot at the time of injury and then you can look for the probable almost certain features of these injuries. This is an example of a maisonneuve fracture where there is syndesmotic widening and medial malleolar avulsion injury on this oblique view on the left. You can see the widening of the tibial fibular clear space and additional small bony fragments in that space. This example on the right is demonstrating the proximal fibula in the same patient where the force has traveled circumferentially through the ankle ascending through the syndesmosis, tearing the interosseous membrane and exiting the proximal fibula. To further our discussion of easily missed fractures, let's discuss the Tillaux fracture. This is the type of fracture that occurs when the anterior tibiofibular ligament tension overwhelms the tibia resulting in an avulsion fracture of the anterior tibial tubercle. The mechanism results from external rotation and abduction of the foot. And in the oblique view, one can see a vertical fracture line extending proximally and communicating with the line in the axial or horizontal plane of the physis.


    Here, in this example on the left, published in easily missed fractures of the lower extremity in radiologic clinics of North America by Yu in 2015, you can see this oblique diagonal fracture heading towards the metaphysis into the physis. On this example, the sagittal example on your right is a CAT scan reconstructed sagittal image demonstrating the coronal oblique fracture line that occurs in this Tillaux fracture which is demonstrated as an intra-articular gap as noted by the bold white arrows. Easily missed fractures, the lateral talar process fracture is a famous area for missing that type of fracture and that's caused by ankle eversion and dorsiflexion and sometimes ankle inversion. This is also known as snowboarders fracture. And it's apparent only on the frontal view. The tip-off is that the soft tissue swelling is distal to the lateral malleolus. Lateral talar process fracture. You can see in this example, on the frontal view, you can see the cortical irregularity which is even more apparent in the oblique view where you can clearly see the lateral talar process fracture fragment. Easily missed fracture, the posterior talar process fracture. An avulsion fracture of the medial tubercle occurs with forceful dorsiflexion and pronation. A chip fracture can occur with excessive plantar flexion.


    And fractures of either the posterior medial or posterior lateral tubercle is best seen in the lateral view. In the lateral view with negative x-rays and high clinical suspicion, it's recommended to go on to CT and you may need to get an externally rotated view if you are going to continue along looking for it on an x-ray. And here example of posterior talar process fractures. In this example A, you have posterior lateral fracture where you can see that there is a fracture line through the posterior process of the talus and also posterior medial process fracture where you see another fracture line to the posterior medial talus. As for easily missed fractures, the anterior calcaneal process fracture is the result of the bifurcate ligament tension in inversion and plantarflexion. It can also be caused by anterior process compression and eversion and dorsiflexion injuries and this is often accompanying missed fracture in car accidents when the foot is jammed into the brake. The best view is on lateral and if it's indeterminate, you can get an oblique view. And what you are looking for is a break in the cortex which is vital to identify the correct diagnosis. And here is an example of an anterior calcaneal process fracture. You really can't see it as well on this example on the left where the anterior process overlies the junction of the anterior subtalar joint which includes the talocalcaneal and navicular articulations. By using an oblique projection, we can remove the navicular from the confounding shadow and we can now identify the oblique fracture which is essentially nondisplaced to the anterior process.


    Easily missed fractures in addition, extensor digitorum brevis avulsion fractures where there is forceful inversion at the dorsal lateral calcaneus and bone fragmentation and this is best visualized in the AP view and you can look for soft tissue swelling distal to the lateral malleolus. And in this example of extensor digitorum brevis avulsion fracture, we can see in this osteopenic patient, a bony fragment that's about 1.5 cm distal to the tip of the lateral malleolus with adjacent swelling consistent with an extensor digitorum brevis avulsion fracture. Other common location of errors that even with the best imaging technique misses might include osteochondral lesions of the talar dome, lesions of the talus, fractures of the cubiod, the cuneiforms, Lisfranc joint and of course regions of complex overlapping anatomy on CT or MRI. Looking at this example to the left of a comminuted medial talar body fracture where identifying on this frontal view of the ankle, medial talar cortical irregularity with the displaced fracture and soft tissue swelling. You cannot see this on a lateral projection though there is a small ankle effusion and possibly a small what's apparent as an os fibula or bone fragment. On the lateral projection, you also then don't notice that when we take the CAT scan, we can see additional fractures, we see a nondisplaced talar neck Hawkins type 1 fracture.


    And we also see a medial talar process avulsion injury noted here at the posterior deep deltoid attachment. The cuboid fracture may be difficult to see on x-ray. Given its overlapping confluence of shadows as identified on this lateral x-ray, it's very hard to see what's clearly seen on a companion CT as an intra-articular cuboid fracture here. And so that brings us to the cost of the delayed diagnosis and the cost may be significant in terms of return to work or inability to maintain your comfortability with running. So in terms of the cost of delayed diagnosis, this can be seen in the imaging through nonunion of fracture sites, secondary osteoarthritis that occurs with joint impaction at the times of injury, the presence of psuedoarthrosis, avascular necrosis from situations like Hawkin's displaced talar neck fracture and of course neuropathic joints and the fragmentation dislocation and debris that accompanies this pathology. So little avulsion fractures may result in big trauma. So it may be just a little indication of what's really going on in there. So in terms of seeing a posterior malleolar fracture, what that means is that the distal fibula was laterally displaced by forceful abnormal talar motion.


    And it almost invariably requires that the rupture -- the syndesmosis has ruptured and the anterior tibiofibular ligament is torn. This strong posterior tibiofibular ligament remains intact but generally avulses off the posterior tibia. And if the ankle reduction occurs prior to the x-ray, an avulsion may be missed. And here is an example of a posterior malleolar fracture and it's important to assess the degree of intra-articular extension and distal tibial plafond involvement. Particularly, large areas of step-off are going to be surgically reduced. Other little avulsion fractures that result from big trauma or associated injuries, no discussion of the lower extremity would be complete without the discussion of the Segond fracture, which is a fracture, sliver fracture that's along the central third of capsule at the lateral tibia invariably associated or almost 75% to 100% associated with ACL injuries and about three quarters of the time associated with meniscal injuries. Segond fractures. So in these two examples, this MRI example on the left demonstrating a lateral tibia plateau fracture. There is bone marrow edema identified and you can see the cortical avulsion at the attachment of the central third of capsule. And you can also identify on this coronal T -- I'm sorry, it's probably a proton density or fluid sensitive sequence.


    You can see the ACL has interstitial high signal within it and on the sagittal image, you can see the disruption of the ACL distal to the mid substance without tibial translation at this time. Little avulsion fractures, that means big trauma, other sites to consider would be to using MRI to assess the soft tissue injury looking at the medial and lateral femoral condyles, the median eminence of the tibia, the fibular head, the medial lateral malleoli, the anterolateral distal tibia, the dorsal talar neck, anterior calcaneal process and bases of second and fifth metatarsals. Moving on to a section regarding sesamoids. Differentiating a bipartite sesamoid versus fracture often proposes a unique challenge to imagers and clinicians alike. Sesamoid bones frequently are multipartite and it's difficult to distinguish fracture versus normal anatomy. Ankle and MTP joints are hot spots for accessory bones. And one must rely on clinical presentation and knowledge of predictable anatomy in order to assess this. Of course runners with forefoot pain, think possible sesamoid stress fracture or stress reaction. Here is an example of bipartite medial sesamoid with an additional transverse avulsion fracture, that's scattered all in that picture.


    And locations of sesamoid vary. This example on the right showing the location variety of sesamoid bones and accessory bones that could be seen. You want to take a history and physical, look at the x-ray for a linear lucency. If it's bipartite, at times it may be curvilinear with sclerosis. Sometimes, you can see periostitis which is seen in sesamoiditis. There can be superimposed sclerosis from AVN. Of course bone erosion with osteomyelitis. And even bone crystals, you can see crystallization and mineralization in the soft tissue and sesamoid and CPPD or calcium pyrophosphate dehydrogenase arthropathy. Sesamoid anatomy is represented here on this rendition of the hallux MTP and sesamoid complex with all the tendons and ligamentous capsular reflection removed. Note the two sesamoid formed in articulation with the hallux called the sesamoid hallucal articulation. They are secured to one another to the intersesamoidal ligament and the plantar capsule is reflected from the attachments of the Abductor and Adductor hallucis musculature and the two heads of the flexor hallucis brevis. Note the plate and lateral collateral ligament complex here denoted with illustration on your right. Regarding the fracture line, we can see the fracture line initially as seen and there is a widening within six weeks as a fracture line osteoclastic activity increases and fibrous layer emerges and then a scaffolding of osseous layer will then heal that bone. Looking at this fracture with -- this chronic fracture evolution. In six months of pain, here we are seeing tibial sesamoid sclerosis.


    And on the MRI, you can see the stress response as noted by bone marrow edema within the two portions of the healed bony bridge. Note the small joint effusion and slight thickening of the sesamoidal phalangeal ligament which remains intact. In this example of sesamoid AVN just to include the complete differential, we are noticing that the sesamoid in this axial view, there is sclerosis at the plantar aspect. And on MRI, you are noticing that there is a geographic T2 line sign and this is part of the spectrum of sesamoid pathologies. In sesamoid osteomyelitis, you can see bony erosion adjacent to soft tissue ulceration which lead to a high clinical suspicion and when you do the MRI, you can see where the red label of S is replaced and this is geographic T1 marrow replacement in a patient who has sesamoid osteomyelitis. In terms of sesamoid crystal deposition, there is erosion and crystal mineralization regarding the proximal pole of the sesamoid as seen in calcium pyrophosphate dehydrogenase. In satisfaction of search, abnormal findings are missed because other ones are found. So your eye just says okay, good and we miss those other ones that you might have to search a little carefully for. And one study showed that initial findings affect the ocurrence of errors. In the presence of nondisplaced fractures, there will often be missed findings whereas severe fractures with high morbidity, there is almost no missed findings. So it's affected by abnormalities and frequency, time pressures and expectation of the findings. Once a particular expected abnormality is found, continue to look for less common ones. In polytrauma status post motor vehicle collusion, you can see multiple fracture dislocation in a satisfaction of search where we may miss the MTP dislocation if we are only focusing on the bases of the metatarsals and of course looking at all views is essential even the soft tissue to notice the gas within the soft tissue and presence of an open fracture. Fractures after hardware placement, overlapping metal can limit hardware and periprosthetic bone fracture visualization. So oblique views may be helpful in this area. Any trauma with forces concentrated at the implant bone interface can be ascertained and fractures typically start at these interface and propagate away. In summary, most missed fractures are result of recognition of errors in predictable regions and careful attention to these regions is important to increase fracture detection. Mechanisms of injury and clinical findings can be very helpful in guiding image interpretation. And further imaging may be needed if results will affect patient management. A list of references is available for review. And I thank you for your time and generous attention.

    TAPE ENDS - [29:45]