THE IE WAS REPLACING A LIFT JACK ON A TRAILER WHEN THE JACK SLIPPED CAUSING THE IE TO JERK HAND AWAY. THE ""JERKING"" MOTION CAUSED THE EMPLOYEE TO STRAIN THEIR R SHOULDER. INITIALLY IT WAS A REPORT ONLY, IE SOUGHT MEDICAL ATTENTION ON 8/14/2023 WHEN EE RECEIVED AN INJECTION MAKING THIS REPORTABLE.