Abstract
The World Health Organisation estimates only 33% of the world's population has local access to diagnostic imaging. Doctors operating in austere locations in Canada and Australia are using point-of-care ultrasound to differentiate between bone injury and soft tissue injury. Studies have demonstrated ultrasound to be a highly sensitive diagnostic tool for bone fracture. We present an ultrasound pictorial review of various bone fractures to demonstrate its value as an extension of the clinical examination in identifying fracture and to support the need for further imaging. Innovative and affordable ultrasound devices have been developed, which will improve accessibility to imaging.
Introduction
Primary care clinicians working in remote locations in Canada and Australia are using point-of-care ultrasound (PoCUS) to differentiate between bone injury and soft tissue injury.1,2 Accordingly, PoCUS is being used as a triaging tool to determine which patients need to travel long distances for radiographs as opposed to those who can be treated locally with rest, ice, compression and elevation.
According to the World Health Organization, only a third of the world’s population has local access to diagnostic imaging; 3 thus over five billion people do not. However, high-quality, affordable ultrasound devices have been developed, which will improve accessibility to diagnostic imaging and may help to fill this gap.
We present an ultrasound pictorial review of bone fractures to demonstrate its value as an extension of the clinical examination in identifying fracture and the need for further imaging. Studies have demonstrated ultrasound to be both sensitive and specific for the diagnosis of bone fracture.4–6
Ultrasound features of fracture
Ultrasound feature of diaphyseal fracture
Traditionally, bone has not been considered amenable to ultrasound because of the high reflectivity at its surface; however, when a bone is fractured it bleeds, and this periosteal fluid can be visualised with PoCUS (Figure 1).
Ultrasound of intact bone cortex. Normal bone is made of dense material containing calcium; bone is highly reflective to ultrasound waves and the cortex of bone appears as a bright white line (arrowheads) with no image beyond.
Figure 2 demonstrates a discontinuation in the bright white, highly reflective cortical line. There is a semicircular black area surrounding the region of the cortical break. Fluid transmits ultrasound waves and is seen as black areas on ultrasound. This is blood from the fracture site and is limited by the periosteum. This is called a periosteal lift and is a diagnostic sign of fracture.
PoCUS in diaphyseal fractures. Ultrasound of diaphyseal fractures demonstrating clearly a periosteal lift; loss of continuity of the cortex with a periosteal haematoma.
Ultrasound features of intra-articular bone fractures
The concept of using periosteal fluid as a surrogate for fractures is well established. Elbow effusions and lipohaemathrosis of the knee are commonly used to diagnose intra-articular fractures on radiographs. The presence of increased joint fluid in a traumatised joint points towards a probable associated bone or joint injury and should direct further investigations. This principle can be applied to any joint such as the hip, knee and elbow (Figure 3).
Periosteal fluid signs. (a) Traumatic elbow effusions are seen by lifting of the anterior fat pad sign.(b) Fat fluid level lipohaemarthrosis of the traumatised knee is used to diagnose intra-articular fractures on radiograph. (c) A hip effusion (starred) in the presence of trauma would indicate an intra-articular fracture of the hip – ‘anterior fat pad sign of the hip’ and would prompt further imaging.
Examples of fractures
Rib fractures
Blunt injury to the trunk is a common presentation to secondary care and can be an area of diagnostic difficulty. PoCUS is a quick, simple and direct imaging method which can help to distinguish between soft tissue injury and rib fracture in blunt thoracic trauma. It allows easier visualisation of a possible rib fracture and therefore the administration of prompt analgesia.
Ribs can be imaged with high-frequency PoCUS and the cortex of the bone can be seen directly (Figure 4). Minor bone displacement, periosteal haematomas and fractures can be demonstrated. In a cross-sectional study by Pishbin et al., 7 ultrasound detected 98% of rib fractures and was quick to perform with an average of 12 minutes to diagnosis. Non-displaced rib fractures are not visible on chest radiographs.
Ultrasound demonstrating disruption in the bone cortex in traumatic rib fracture.
Sternal fractures
Approximately 10% of patients admitted with blunt trauma injuries will have a sternal fracture, and ultrasound has been shown to be 100% sensitive and specific for diagnosing sternal fractures. 5
Figure 5 demonstrates clearly a minimally displaced sternal fracture on ultrasound, which is also visible on computed tomography (CT). Non-displaced sternal fractures are not visible on radiographs.
CT and ultrasound image of a fracture of the sternum. (a) A minimally displaced fracture of the sternum on sagittal CT. (b) The same fracture on ultrasound via a corresponding step in the bright white cortical lines.
Lower leg fracture
Figure 6(a) demonstrates a depressed cortical comminuted fracture of the neck of the fibula. Figure 6(b) is an ultrasound image of the same fracture. The ultrasound image again demonstrates a loss of continuity of the bright white cortical line with black fluid anterior to the cortical steps as shown by the arrows. Figure 7 demonstrates a cortical break in the distal tibia on PoCUS. A study of 122 patients with ankle trauma used ultrasound performed by junior orthopaedic surgeons who had undergone a 30-minute basic ultrasound training session to guide triage. 8 In this study, PoCUS was used as an extension of the Ottawa ankle rules to exclude ankle fractures and demonstrated that, with limited standardized training, ultrasound guided triage can be used to exclude at least significant ankle fractures and identify those requiring further imaging.
X-ray and ultrasound image of a comminuted fibula neck fracture.
Distal tibia and fibula fracture. Top row: X-ray demonstrates a non-displaced distal tibia and fibula fracture. Middle row: ultrasound demonstrates an obvious cortical break of the distal tibia. Bottom row: X-ray reveals the distal tibia and fibula fracture after displacement.
Metatarsal fracture
Radiographic and ultrasonic images of a patient’s third metatarsal are shown in Figure 8(a) and (b). The ultrasound examination was performed due to the patient complaining of ongoing forefoot pain in the region of the neck of the third metatarsal. Ultrasound at the site of pain demonstrated a periosteal irregularity, which was a healing stress fracture. This is seen indicated with the arrows on the radiograph of the neck of the third metatarsal.
Radiograph and ultrasound image of the third metatarsal in a case of ongoing forefoot pain.
PoCUS has been found to have a significant sensitivity 87.3% (95% confidence interval (CI) = 77.5%–93.4%) and specificity 96.4% (95% CI = 93.1%–98.2%) for the diagnosis of fifth metatarsal, lateral and medial malleolus fractures in a study of 246 patients presenting with a foot and/or ankle sprain. 4
Hip fracture
PoCUS shows promise in selecting out hip trauma patients for magnetic resonance imaging (MRI) examination. A study by Safran et al. 6 demonstrated that sonography screening for occult hip fractures was 100% sensitive. In total, 30 patients with low-energy trauma to the hips and inconclusive hip radiographs were recruited to the study and had a PoCUS scan of the hip, followed by MRI. PoCUS successfully identified trauma in all patients with subsequent confirmed fracture on MRI (n = 10) and seven additional – three of which demonstrated pubic rami fracture and four false positives. Therefore, their results indicate that PoCUS can aid in the clinical exclusion of intra-articular trauma and a positive finding should be followed up with more advanced imaging techniques such as MRI. Figure 9 is an example of a PoCUS captured image demonstrating hip effusion and the corresponding radiograph.
Fifty-year-old male involved in a road traffic accident complains of hip pain. PoCUS effectively demonstrates hip effusion, which in the presence of trauma is most likely fracture.
Approximately 15% of hip fractures are impacted neck of femur fractures (often in a sub-capital position), are non-displaced and are not visible using X-ray. This is because in non-displaced hip fractures, there is often no fracture line visible, with preservation of Shenton’s line plus the hip trabeculae may also be intact. Moreover, it is recognised that some patients with non-displaced hip fracture can weight-bear, straight-leg raise and demonstrate normal axial compression on initial presentation. PoCUS can be used in this situation as an extension of the clinical examination to guide the need for further imaging.
Figure 10 is a set of radiographic images of a 70-year-old woman who had a fall onto her left side and was admitted with severe left hip pain. Figure 10(a) is the initial radiograph taken on admission. She failed to mobilise well on the ward and so repeat pelvic radiography was performed three days later (Figure 10(b)) followed by CT (Figure 10(c)).
Non-displaced sub-capital fracture. (a) Left occult hip fracture demonstrating preservation of Shenton’s line and hip trabeculae. (b) Hip radiograph three days later demonstrating displaced left hip fracture. (c) CT of the left hip demonstrating fracture.
Hip ultrasound is a quick and easy screening tool for hip effusions and each side can be compared. The presence of a joint effusion in a traumatised hip is often associated with fracture and should prompt further definitive imaging techniques.
Conclusion
PoCUS is being used in remote areas of Australia and Canada as an initial screening tool to differentiate between soft tissue injury and bone injury – an extension of the clinical examination. For the two-thirds of the world’s population without access to basic diagnostic imaging, this would be of great use to identify the need for further imaging. The emergency department in secondary care settings would also benefit from PoCUS of minor trauma preventing missed fractures and increasing the accuracy and appropriateness of referrals to fracture clinics.
PoCUS is cheap, safe and quick to perform and is easy to learn and become competent in its operation and interpretation.
Footnotes
Acknowledgements
Dr Hylton Meire and Professor Paul Sidhu (Consultant Radiologists at Kings College Hospital, London).
Contributors
Hammad Qadi (International Committee of Medical Journal Editors criteria 1, 2, and 3); Juliet Davidson (ICMJE criteria 1 and 2); Michael Trauer (ICJME criteria 1 and 2); and Richard Beese (ICMJE criteria 1, 2, and 3).
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Ethics Approval
Not applicable.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Guarantor
Richard Beese.
