A 44-year-old left-hand dominant carpenter experienced immediate left elbow pain after trying to stop a heavy object from falling two days ago. Figure A shows a clinical image of the patient upon presentation. Physical exam shows full strength with wrist flexion, wrist extension, and pronation, but notable weakness with supination of the forearm. Sensory exam shows no deficits in the forearm or hand. There is a negative milking maneuver test and a positive hook test. Radiographs are shown in Figure B. What is the next most appropriate step in management?