Complex sentence: However, the idea that SCI was untreatable remained predominant until the early 20th century; it was not until the latter half of the century that breakthroughs in imaging, surgery, medical care, and rehabilitation medicine contributed to a substantial improvement in SCI care.
Split into simpler sentences: However, the idea that SCI was untreatable remained predominant until the early 20th century. It was not until the latter half of the century that breakthroughs in imaging, surgery, medical care, and rehabilitation medicine contributed to a substantial improvement in SCI care.