Keywords ultrasound - Computed tomography - Radial head fracture
Introduction
Indirect elbow trauma is caused by a fall onto the extended arm, which results in spraining of the elbow joint. The axial force is transmitted to all 3 bones involved in the joint. In case of a resulting fracture or dislocation, patients usually hold the affected elbow and forearm fixed with the opposite hand, so that movement of the injured joint is avoided.
The elbow joint is easily accessible for sonographic examination [1 ]
[2 ]
[3 ]
[4 ]. In addition to the disruption of osseous surfaces, hemarthrosis in the anterior and posterior joint areas can also be diagnosed very easily [5 ]. Such a hemarthrosis corresponds to the so-called “fat pad sign” on the conventional lateral radiograph and is considered an indirect fracture sign.
X-rays (XR) are currently the standard modality for the diagnosis of bone fractures in the lower or upper limbs in emergency departments (ED). However, point-of-care ultrasonography (POCUS) is a diagnostic alternative with some obvious advantages, especially in the ED setting. It does not require the patient to fix the bone of interest in a stable and uncomfortable position, allows observation of the bone and joints under movement by the patient or the sonographer, can be performed directly at bedside, and avoids exposure to radiation. Indeed, POCUS is the standard modality for the diagnosis of bone fractures in the extremities in children, which is also supported by empirical evidence [6 ]
[7 ]
[8 ].
Recently, there has been increased focus on the role of POCUS in adult fracture detection, which is evident in overview papers, systematic reviews, and guidelines [9 ]
[10 ]
[11 ]
[12 ]
[13 ]
[14 ]. A systematic review [10 ] still concludes that the current evidence is too limited to support the use of US as an initial diagnostic tool for fractures in adults.
When performing comparisons between XR and POCUS, computer tomography (CT) is typically used as the reference standard. This choice reflects the implicit assumption that POCUS is not superior to CT. The case series presented in this paper tries to provide a more nuanced picture about the diagnostic information provided by POCUS and CT, respectively.
Elbow fractures are a specific group of fractures with high relevance for ED settings. The most common fracture among these injuries is a radial head fracture by far, as the axial force exerted by the capitulum humeri during indirect compression trauma leads to a bursting effect at the radial head. If there is no displacement of the radial head fragments, patients can still move the elbow to some extent. Often it is only later, after a hemarthrosis has formed, that significant limitations in mobility occur. As a result, patients frequently seek care in the ED hours later. In this emergency setting, an accurate diagnosis is essential for initiating appropriate treatment. Frequently, a conventional XR series of the elbow (ap/lateral view and Norman view) is initially performed, and in cases of uncertainty, CT or magnetic resonance imaging is often employed.
In our ED, XR and/or US are routinely used as the primary diagnostic tool for all patients with indirect elbow trauma. The choice depends on the personal US skills of the emergency physician in charge. In addition, a cone beam CT (CBCT) examination is often performed, if fracture signs are visible on US or XR. Plain radiographs and CBCT are evaluated routinely by the radiology department, whereas US is evaluated directly by the emergency physician. This provided our ED staff with the opportunity to gain experience regarding the diagnostic utility of all 3 modalities.
Our emergency physicians noticed cases in which radial head fractures were just as clearly visible on US as on CBCT, while these fractures were not visible on XR ([Fig. 1 ]). In addition, they observed that US can be more informative than CBCT or that the knowledge of the US image can change the interpretation of CBCT images. We decided to systematically identify cases illustrating these points in order to share this experience with the scientific community.
Fig. 1 Illustration of a radial head fracture detected on US examination (indicated by yellow arrows), not yet visible on XR. The sole indirect indicator of the fracture on XR is the fat pad sign. H = hemarthrosis.
Methods
Sonographic examination
The sonographic examination of an injured elbow is performed in our ED as shown in Figures 2–4. The patient’s forearm is comfortably positioned on a horizontal surface, with the elbow joint not resting on it. The displayed images depict the physiological conditions of an uninjured elbow. The fossa olecrani shown in [Fig. 2 ] contains no fluid in this case and appears sonographically hyperechoic. [Fig. 3 ]a shows the circumference of the radial head in the short-axis view (SAX). If the pain level allows, the hand of the affected arm can be rotated gently to observe whether the radial head moves within the annular ligament ([Fig. 3 ]b). [Fig. 4 ] depicts the longitudinal position of the ultrasound probe (long-axis view, LAX), allowing assessment of both the radial head and neck. In this position as well, the hand can be rotated gently to visualize all sides of the radial head and neck.
Fig. 2 Clinical situation and LAX-US image of the dorsal side of the elbow: physiological representation without hemarthrosis in the olecranon fossa.
Fig. 3
a Clinical situation and SAX-US image of the radial head: smooth bone surface of the circumference beneath the annular ligament. b SAX examination of the radial head: careful rotation of the hand shows the rotation of the radial head.
Fig. 4 Clinical situation and LAX-US image of the radial head, the radial neck, and the capitulum of the humerus.
Selection of patients for the case series
All 91 patients diagnosed in our ED with a radial head fracture between January 2021 and November 2022 were identified. Forty-five patients were diagnosed using US, and 18 of these patients also received a CT scan. The first author reviewed the US, XR, and CBCT images of these patients and selected examples illustrating the variation in coincidence and discrepancy between US and CBCT. Ten patients were asked for consent to publish their images, and 8 gave their consent.
Structure of case descriptions
The routine description of the US findings by the emergency physician was compared with the routine description of the CBCT scan by the radiologist. In the following, we first present for each patient the diagnostic findings from US under the heading “US” and then report the coincidences and discrepancies with the routine description under the heading “r-CBCT”. If a reevaluation of the CBCT examination performed by us with knowledge of the US findings allowed confirmation of additional US findings, they are reported under the heading “CBCT+”. Completely new findings are noted under the heading “CBCT++”.
Case descriptions
Fig. 5 Case 1: Three selected views of the US examination and slices of the CBCT examination. Signs of hemarthrosis are marked with H. A radial neck fracture can be diagnosed on CBCT (red arrow).
This 24-year-old patient fell off his bike the day before and landed on his left arm. The left elbow was swollen and had bluish discoloration. There was tenderness over the radial head, and limited pronation and supination of the hand. US: Pronounced fresh hemarthrosis in the olecranon fossa and bony contour disruption of the circumference of the radial head, which, however, rotated easily in the annular ligament. In addition, there was a periosteal hematoma at the radial neck as a sign of fracture extension to the radial neck. r-CBCT: Only the fracture of the radial head but not that of the neck was diagnosed. CBCT+: Osseous step of the radial neck (red arrow in sagittal view).
Fig. 6 Case 2: Three selected views of the US examination and slices of the CBCT examination. Hemarthrosis is marked with H. The fracture of the radial circumference can be diagnosed on CBCT (red arrow).
A 41-year-old patient fell off her bike 9 days ago and landed on her right elbow. X-rays taken on the same day at an external ED showed no pathology. Due to persistent pain and limited movement of the elbow, she presented at our ED. US: Distinct but already hypoechoic hemarthrosis in the olecranon fossa and 0.7mm step in the circumference of the radial head, which rotated easily in the annular ligament. r-CBCT: Only a subcapital radial neck fracture was diagnosed without involvement of the articular surface (arrow in the sagittal view), which was not seen on US. CBCT+: Step in the circumference of the radial head (red arrow in the axial view).
Fig. 7 Case 3: Three selected views of the US examination and slices of the CBCT examination. Hemarthrosis is marked with H. Consistent findings of US and CBCT.
A 48-year-old patient was referred to our ED by a general practitioner after slipping and falling on her right arm. The painful right elbow had previously been X-rayed and found to be inconspicuous. The elbow showed no external abnormalities, but joint mobility was slightly restricted in every direction. US: Pronounced hemarthrosis in the olecranon fossa and the coronoid fossa, as well as a chimney phenomenon and minimal osseous contour interruption of the circumference of the radial head. r-CBCT: Confirmation of the non-displaced intra-articular radial head fracture and joint effusion.
Fig. 8 Case 4: Three selected views of the US examination and slices of the CBCT examination. Hemarthrosis is marked with H. The extension of the fracture into the radial neck can been diagnosed on CBCT (red arrow).
A 38-year-old patient who fell off his skateboard and landed on his right arm. The elbow showed no external injuries but was painful with movement restriction in every direction. US: Pronounced hemarthrosis over the trochlea humeri and in the olecranon fossa, as well as minimal contour interruption of the circumference of the radial head with a small chimney phenomenon. r-CBCT: Diagnosis of a non-displaced intra-articular radial head fracture. CBCT++. Extension of the fracture into the radial neck (red arrow in the coronal view).
Fig. 9 Case 5: Three selected views of the US examination and slices of the CBCT examination. Hemarthrosis is marked with H. Consistent findings of US and CBCT.
A 77-year-old patient stumbled over a curb and caught herself with her left arm, resulting in an elbow extension deficit. She presented at our ED several hours later. US: Significant hyperechoic hemarthrosis in the olecranon fossa, as well as an irregularity of the radial neck. The circumference of the radial head was unaffected. r-CBCT: The subcapital, non-intraarticular fracture of the radial head was confirmed.
Fig. 10 Case 6: Three selected views of the US examination and slices of the CBCT examination. Hemarthrosis is marked with H. A radial neck fracture can be diagnosed on CBCT (red arrow).
This 63-year-old patient fell off her bicycle and caught herself with her left arm, resulting in increasing restriction of movement and pain in the left elbow. US: Hemarthrosis in the olecranon fossa, small step in the area of the collum radii, and an undisplaced contour interruption of the circumference of the radial head. r-CBCT: Only the intraarticular fracture of the radial head could be confirmed, but it was described as mildly displaced and impacted. CBCT+: Fissure in the radial neck (red arrow in the coronal view).
Fig. 11 Case 7: Three selected views of the US examination and slices of the CBCT examination. Hemarthrosis is marked with H. Bony avulsions from the humeral radial epicondyle can be diagnosed on CBCT (red arrow).
A 75-year-old patient who slipped on wet ground and fell on her left side. Over the next few hours, she complained of increasing pain in her left elbow. Clinically, tenderness was found over the radial head, and mobility of the joint was restricted in every direction. US: Hemarthrosis in the olecranon fossa, as well as contour interruption of the radial head and step in the radial neck. r-CBCT: Slightly displaced subcapital extra-articular fracture of the radial head, as well as of the circumference. In addition, small bony avulsions from the radial epicondyle as well as a lateral avulsion of the proximal ulna were noted (red arrow in coronal view), which were not seen on US.
Fig. 12 Case 8: Three selected views of the US examination and slices of the CBCT examination. Hemarthrosis is marked with H. Consistent findings of US and CBCT concerning the radial head. A fracture of the radial neck can be diagnosed on CBCT (red arrows).
This 45-year-old patient fell off his bicycle and landed on his right side. Due to painful movement restriction in his right elbow, he came to our ED. Clinically, a contusion mark was found over the radial epicondyle of the humerus as well as tenderness over the head of the radius. Pronation and supination were painful and limited. US: Significant hemarthrosis in all planes, as well as a disruption of the contour of the circumference of the radial head without any disruptions of the radial neck. r-CBCT: A non-displaced subcapital extra-articular fracture of the head confirmed the US finding. In addition, the involvement of the neck of the radius could be diagnosed, which was not seen on US (red arrows in coronal and sagittal views).
Discussion
Accurate diagnosis of indirect elbow injuries is essential in the ED to initiate adequate initial treatment. If patients can still move the painful elbow, albeit with limitations, an initial diagnostic US evaluation can be quite useful. Ultrasound machines are typically available in most EDs today, and even inexperienced emergency physicians can easily diagnose hemarthrosis in the olecranon fossa with US. If such hemarthrosis is present, an intra-articular fracture should be consistently sought.
Barret et al. [4 ] have already demonstrated that immediate sonographic examination of traumatized elbows in EDs by orthopedic specialists is feasible. However, their case series primarily focused on injuries to ligamentous and tendinous structures, which are less relevant for initiating emergency treatment since conservative approaches are generally employed. The examination time in their study was relatively long, ranging from 24 to 30 minutes.
We, therefore, directed our attention to osseous injuries. Our case series highlights that, in the clinical routine of diagnosing elbow fractures, POCUS can be more informative than CBCT or vice versa and that knowledge obtained from the US examination can help to interpret CBCT images correctly. Actually, in 2 patients POCUS was more informative than the routine description of the CBCT (cases 1 and 6), in 2 patients POCUS was less informative (cases 7 and 8), they were equally informative in 3 patients (cases 3, 4, and 5), and each modality made a contribution of its own in one patient (case 2). In addition, knowledge of US findings improved the interpretation of CT images in 3 patients (cases 1, 2 and 6).
This suggests that the joint application of US and CT is advisable if correct diagnosis of the extent and components of the fracture is of uttermost importance. This may apply in research settings. In the clinical setting, the most accurate diagnosis of fracture extent may be less relevant as the choice of treatment will usually remain conservative. Indeed, the clinical consequences would not have been impacted by the choice of the diagnostic modality in any of the 8 cases included in this case series.
It is noteworthy that suspicion of a non-displaced radial head fracture was raised in the routine report based on the CBCT finding in 1 of the 18 patients, while neither hemarthrosis nor any other fracture signs could be depicted sonographically. Only our retrospective analysis revealed that the subtle fracture lines on CBCT were caused by significant motion artifacts during the examination. This highlights the advantage of POCUS which allows an accurate examination of the elbow irrespective of its current movement. Furthermore, the joint can be comfortably positioned during the US examination. In addition, for a CBCT examination, the elbow joint needs to be almost fully extended, which can be associated with significant pain in cases of intra-articular fractures. US can be performed in the flexed position of the elbow, which is preferred by patients. In addition to avoiding radiation exposure, these aspects should be taken into account when comparing the clinical value of both modalities.
However, an absolute prerequisite for sonographic examination is precise anatomical and sonographic knowledge on the part of emergency physicians. This requires corresponding educational efforts [7 ]
[10 ].
With respect to the long-term perspective of using US to detect radial head fractures, the potential role of artificial intelligence (AI) has to be taken into account. Today, AI approaches for detecting fractures on radiographs are already widely available [15 ]. However, investigations with respect to combining AI techniques with sonography are still limited [16 ]
[17 ]. This may reflect that the crucial issue with sonography is less the task of image interpretation and more the art of generating interpretable images. Furthermore, these 2 cited studies compare the reliability of AI-assisted US with conventional X-rays for pediatric radius fractures. CT scans are less relevant in this group, as a radiation-sparing examination method is of utmost importance. Additionally, in the examination of wrist injuries, US can be performed with the forearm completely immobilized. Pronation and supination, as required in our investigations, are not necessary in this context.
To date, there is no reliable study on the use of AI in the US examination of radial head fractures.
