X-rays (XR) are today the standard modality for the diagnosis of bone fractures in the lower or upper limbs in the emergency room. Point-of-care ultrasound (POCUS) is an alternative with some obvious advantages especially in the emergency room setting: It does not require the patient to fix the bone of interest in a stable position, allows observing the bone and joints under movement by the patient, can be performed at bedside, and avoids the exposure to radiation.

The advances in ultrasound technology has increased the interest in using POCUS as an alternative to XR in recent years. POCUS is used routinely prior to XR at the ORTHO-NOTFALL of the Merian Iselin Klinik Basel (MIK) in patients with suspicion for an indirect elbow trauma. It is the aim of this project to use this constellation in order to contribute to a systematic comparison of the value of the two modalities with the long-term aim to establish POCUS as the first-line diagnostic tool.

As a fist project, the SONOELB study was initiated. This study aims at a comparison of the diagnostic accuracy between XR and POCUS using CT as reference. The project started in October 2022 and aims at enrolling 130 patients until March 2025. The project is financially supported by the Merian Iselin Science Research PLC.

Objective:

The primary objective is to compare the diagnostic accuracy of POCUS and XR with respect to diagnosing fractures of the elbow after an indirect elbow trauma in the ED setting and to investigate the rate of agreement between the two modalities.

The primary outcome is the difference in diagnostic accuracy between the two modalities with respect to diagnosing a radial head fracture and the degree of agreement between the two modalities.

Secondary outcomes are the difference in diagnostic accuracy between the two modalities and the rate of agreement with respect to the other fracture types, to the decisions "any fracture", and to the decision "any fracture other than radial head".

Experimental Intervention (medical device) POCUS: The ultrasound examination of the injured elbow includes seven standard settings. The probe is placed on the joint in four ventral and in three posterior positions. If hemarthrosis is detected, this is always suspicious of a possible intra-articular fracture. Even the smallest amounts of blood can be detected sonographically.

The surfaces of the bones involved in the joint (humerus, ulna, radius) are accurately displayed in all seven sonography settings. Disrupted bone surface indicates a fracture.

POCUS will be performed according to the local SOP.

Control Intervention (standard/routine/comparator) XR: The conventional radiograph of the injured elbow consists of three standard views: ap, lateral and Norman oblique. This X-ray examination is the most commonly performed technique to date to diagnose an injured elbow.

CBCT (Cone Beam Computed Tomography): The injured elbow is placed in an almost most extended position in the CBCT tube. For this purpose, the affected arm is placed and fixed on a carbon-splint. The examination time is about 40 seconds XR will be performed according to the standard procedures of the ED of the MIK. The same holds for CBCT.

Any of the three diagnostic procedures applied can be discontinued in the case of patient discomfort, harm, or risk of harm according to the standard procedures of the MIK.

Compliance of the staff of the ED with performing the three modalities is supported by SOPs and internal training.

In the case of withdrawal of a patient, the reasons are recorded on the CRF. The data of these patients will not be included in the statistical analysis. The data will not be deleted in the data management system. Patients who withdraw themselves are offered a chat with the PI and further consultations.

Patients included in the trial will follow the standard management at the MIK. There are only two changes:

• a CBCT is performed in addition after having performed both POCUS and XR, if there are no positive findings on POCUS or XR.
• an additional blinded evaluation of all CBCTs will be done by one independent rater.

CBCT will be ordered by the staff of the ED in all patients and may be preliminary evaluated. However, these evaluations will not be documented as part of this study. They are also not accessible for the staff at the Radiology Department in the routine evaluation of the XRs.

Inclusion Criteria:

• Informed Consent signed by the subject
• Suspicion for an indirect elbow trauma as part of the routine management at the ED of the MIK.

Exclusion Criteria:

• Age below 18
• Patients who are lacking capacity of judgment
• Patients with (temporary) cognitive impairment which makes an understanding of the patient information unlikely
• Patients with limited knowledge of German or English which makes an understanding of the patient information unlikely
• Patients with contraindications for US, XR or CT.
• Lack of informed consent

The two modalities to be compared (POCUS and XR) and the reference standard (CBCT) will be applied in a consecutive series of 130 patients with a suspicion of an indirect elbow fracture at the emergency department of a single center. All investigations will be part of the initial, single visit of the patient at the emergency department.

The modalities will be evaluated blinded for each other. The design is well known as a comparative, paired accuracy study. The design allows to estimate the accuracy of the two diagnostic modalities and the corresponding difference as well as the agreement between the two modalities.