Complex sentence: While working at the Northern Pacific Hospital in Missoula, Watkins sustained severe burns on his left arm from the use of an old X-ray machine, which limited his physical capacity to continue his medical practice and resulted in his "virtual retirement" in approximately 1934.
Split into simpler sentences: While working at the Northern Pacific Hospital in Missoula, Watkins sustained "severe burns" on his left arm from the use of an old X-ray machine. The burns later limited his physical capacity to continue his medical practice and resulted in his "virtual retirement" in approximately 1934.