According to the results of the interim analysis when 50% of the targeted sample size was reached, a statistically significant benefit was detected with a large effect size in one treatment arm. For this reason, the study was terminated prematurely.

This study is designed as a randomized controlled study. The investigators aim to compare the success of supination-flexion and hyperpronation maneuvers in the treatment of preschool children presenting to the emergency department with radial head subluxation.

All children aged 0-6 years, who are diagnosed with radial head subluxation secondary to traction of the forearm, had no evidence of direct trauma to the arm or fracture in the arm (no deformity, swelling, ecchymosis), had no history of musculoskeletal disease, and are approved to participate in the study by their legal guardians, will be included in the study. Patients who are considered to have radial head subluxation initially but had an X-ray performed by the physician and had a fracture in the arm will be excluded from the study.

In the study, patients will be randomized and assigned to two treatment groups: the supination-flexion group and the hyperpronation group. In the supination-flexion group, the forearm will be supinated first, followed by full flexion of the elbow joint. In the hyperpronation group, the forearm will be pronated with the child's palm facing down. In both groups, maneuvers will be performed by 3 emergency medicine specialists with at least 2 years of experience.

First-attempt failure is determined as the primary outcome of the study. Failure in the second attempt, ultimate failure, recurrence, patient satisfaction during the procedure, pain intensity (assessed by the Face, Legs, Activity, Cry, Consolability - FLACC pain scale), and treatment-related adverse events are determined as secondary outcomes of the study.

The investigators calculated the sample size and decided to include 117 patients in each group.

INTRODUCTION Radial head subluxation also called nursemaid's elbow and pulled elbow, usually results from a sudden pull on the outstretched arm and is the most common cause of upper extremity injuries in preschool children. The diagnosis is made clinically and there is no need for routine imaging. The child complains of pain and refuses to use the affected arm. Radial head subluxation is treated with manual reduction of the subluxated radial head. Among the various reduction maneuvers available, the commonly used methods are supination-flexion and hyperpronation maneuvers.

The issue of which maneuver is more successful is still controversial. Supination-flexion is generally accepted as the standard maneuver and is the most preferred method. However, the hyperpronation technique was reported to be superior in a 2017 Cochrane review with 8 articles. But in a more recent randomized controlled trial on 152 patients it was reported that the supination-flexion maneuver was more successful. Controversial is not just the contradiction of previous study results. In addition, the quality of evidence is also controversial, as previous studies carry a high risk of bias. There is a serious risk of selection bias in most of the studies due to the lack or insufficiency of randomization or allocation concealment. Again, since there is no assessor blinding in the majority of the studies, the risk of detection bias is inevitable. Furthermore, in most of the previous randomized controlled trials, the sample size was not calculated. As a result, as highlighted in the Cochrane review, most previous randomized controlled trials, have a high risk of bias. The investigators think that well-planned, low-bias randomized controlled trials, are needed to answer this clinical question, both due to the high risk of bias in previous studies and conflicting results regarding which maneuver is superior in published reports.

In this randomized controlled study, the investigators aimed to compare the success of supination-flexion and hyperpronation maneuvers in the treatment of preschool children presenting to the emergency department with radial head subluxation.

METHODS This study will be conducted and reported in accordance with the Consolidated Standards of Reporting Trials (CONSORT) 2010 statement.

Design This parallel group open-label randomized controlled trial will be conducted between May 2023 and May 2024 in a tertiary education and research hospital.

Ethics committee approval was obtained from the local ethics committee of Umraniye Training and Research Hospital (Ethics Committee approval date: 21 March 2023, approval number: 211913807).

Population All children aged 0-6 years, who will be diagnosed with radial head subluxation secondary to traction of the forearm, had no evidence of direct trauma to the arm or fracture in the arm (no deformity, swelling, ecchymosis), had no history of musculoskeletal disease, and will be approved to participate in the study by their legal guardians, will be included in the study. Patients who are considered to have radial head subluxation initially but had an X-ray performed by the physician and had a fracture in the arm will be excluded from the study.

Diagnosis The patients will be diagnosed with radial head subluxation clinically, and if the child shows symptoms of pain after traction on the arm and refuses to use the arm on that side, the diagnosis of radial head subluxation will be made. In cases where routine imaging will not be requested, but the history and physical examination are not clear, imaging will be requested at the discretion of the physician managing the patient.

Interventions In the study, patients will be randomized and assigned to two treatment groups: the supination-flexion group and the hyperpronation group. In the supination-flexion group, the forearm will be supinated first, followed by full flexion of the elbow joint. In the hyperpronation group, the forearm will be pronated with the child's palm facing down. In both groups, maneuvers will be performed by 3 emergency medicine specialists with at least 2 years of experience.

Outcome measurements First-attempt failure is determined as the primary outcome of the study. 10 minutes after the procedure, the patient will be re-examined and the success of the treatment will be evaluated. If additional treatment is needed or if the child still avoids using his/her arm after the procedure, it will be considered a treatment failure. If the participant's pain decreases and the participant can use the effected arm easily, the maneuver will be considered successful.

Failure in the second attempt, ultimate failure (failure after the third reduction attempt), recurrence (re-admission with radial head subluxation in the same arm within 72 hours), and pain intensity of the patient (will be assessed by the Face, Legs, Activity, Cry, Consolability pain scale (FLACC)), treatment-related adverse events (fracture of the forearm, hyperemia, vascular injury, nerve injury after the first attempt) are determined as secondary outcomes of the study.

Randomization Randomization will be done via www.randomizer.org and in 6 blocks. Treatment allocation will be concealed and performed by means of a computerized balanced allocation method.

Blinding The study is not suitable for blindness since two different maneuvers will be applied as intervention and therefore it was designed as open-label. However, the accessors will be blinded to the study.

Sample Size Calculation G*Power 3.1.9.6 software was used for sample size calculation. In studies comparing two reduction methods in the literature, the failure rate at the first attempt was reported as 16.2-34.2% in the supination-flexion group and 4.4-20.9% in the hyperpronation group. In addition, in the Cochrane review, which compared both reduction methods and was published in 2017, the failure rate in the supination-flexion group was reported as 26.4%. The supination-flexion group was considered the control group, and a 15% reduction in failure was considered clinically significant. To detect such a difference, it was calculated that 106 patients should be included in each group using a two-sided alpha value of 5% and a power of 80%. Finally, considering the potential data loss of 10%, it is decided to include 117 patients in each group.

Statistical analysis SPSS 26 (IBM Corp. Released 2019. IBM SPSS Statistics for Windows, Version 26.0. Armonk, NY: IBM Corp.) will be used for statistical analysis. The normal distribution of continuous data will be determined by the Shapiro-Wilk test and histograms. Normally distributed data will be expressed as mean and standard deviation and non-normally distributed data will be expressed as median and quartiles. The Student-T test will be used for the comparison between groups for continuous data with normal distribution, and the Mann-Whitney U test for those without normal distribution. Categorical data, such as primary outcome treatment failure rates, will be expressed as frequency and percentage, and the Chi-square test will be used for group comparison for categorical variables (Fisher's exact test where necessary).

A statistically significant level of p<0.05 was accepted.

Inclusion Criteria:

• Clinical diagnosis of radial head subluxation
• No evidence of direct trauma to the arm
• No fracture in the arm
• No history of musculoskeletal disease

Exclusion Criteria:

-Refusing to participate in the study

The primary outcome accessors will be blinded to the study. They will not know which group is supination-flexion group or hyperpronation group from the data set. Group names will be included in the dataset as group 1 and group 2.