What is the subject of Bilah""?
Ri Kara: It is Shevet Evraso (1). Only now it explains what the staff does.
What is the meaning of "Bilah"?
Rashi #1: This is like "l'Vul Etz" (Yeshayah 44:19, i.e. corrosion).
Rashi #2: This is like "veha'Aretz ka'Beged Tivleh" (Yeshayah 51:6) - "Shachvu la'Aretz Chutzos Na'ar v'Zaken" (2:21). They did not have pillows or blankets; their flesh wore out when they were exiled.
Why does the verse distinguish bones from flesh and skin?
Ibn Ezra: Flesh and skin feel; it suffices for them to decay (Magihah in Toras Chayim - the person is pained). Bones do not feel, so they were broken.
Palgei Mayim: If a bone is broken, if the skin and flesh are not intact, it cannot heal. So, my Tzadikim were taken from me; my hope to heal is lost.