These photos should illustrate why its called the Knuckles. Its the knuckles of a closed fist. The whole range is given the same name.
The Sinhala word for this mountain range is Dumbara Kanduwetiya. i.e. Dum=Smoke/Mist Bara= Heavy/Laden Kanduwetiya= Mountain Range. i.e. A direct translation would be Mist Laden Mountain Range.
Below two photos: View from West (Near Hulu Ganga, MadolKelle) looking east
Below Two photos: View from East (Tennekumbura, Kandy, Mahiyangana Road) looking West