This group received the teaching intervention and was evaluated before and after the intervention. Improvement was compared to their performance prior to the intervention.

Participants were enrolled in a musculoskeletal ultrasound course including 2 components:

• An online course (1-2 hours) to be done before the practical session. The videos were made available one (1) month prior to the practical course. This component reviewed the basics of ultrasonography, as well as the normal and abnormal appearance of relevant musculoskeletal structures (bone, tendon, ligaments, muscles, bursas, and nerves), and the ultrasound anatomy of high yield regions of the musculoskeletal system (shoulder, elbow, knee, ankle)
• A practical session (4-6 hours) done during one of the usual academic days of the orthopedic residency program. This session covered the use of the ultrasound; the examination of the shoulder, elbow, knee, and ankle; ultrasound-guided musculoskeletal injections and aspirations; and ultrasound-guided distal radius fracture reductions. Ample practice time was given to the residents using means such as phantom models, cadavers, and real patients.

A 13 questions written examination was given to the residents using an online platform at each endpoint. The exam covered the basics of ultrasound physics; how to use the machine; the normal and pathologic appearance of tendons, ligaments, and muscles; and ultrasound appearance of the musculoskeletal anatomy described in the course. The score was reported on a scale from 0 to 100, with 100 being the best score.

A 13 questions written examination was given to the residents using an online platform at each endpoint. The exam covered the basics of ultrasound physics; how to use the machine; the normal and pathologic appearance of tendons, ligaments, and muscles; and ultrasound appearance of the musculoskeletal anatomy described in the course. The score was reported on a scale from 0 to 100, with 100 being the best score.

Each participant underwent a practical examination assessing ultrasound proficiency at each endpoint. The residents were assessed by one of the author of the study on their ability to perform a shoulder ultrasound exam as well as the different tasks related to the MSK-US. For each task, the assessor rated the participant on a scale of 0 to 2, where :

• 0 means an inability to perform the task,
• 1 means the task is only partially completed,
• 2 means that the task that is performed correctly.

The final score was then be calculated and reported in percentage (with 100 being a perfect score) for the analysis.

This questionnaire was presented to participants once at the moment of their inclusion in the study. It covered the residents' level of training (post-graduate year), age, sex, the amount of prior exposure to ultrasound (in approximate hours), and the different settings in which the residents have been exposed to MSK-US.