殿筋 is read as でんきん (denkin) and means gluteus.
でんきん
denkin
だいでんきん
gluteus maximus
でんかく
palace
ふっきん
sit-up (exercise)
すじ
(Edo period) counter for hundreds of mon (obsolete unit of currency)
てっきん
reinforced concrete
あらすじ
outline
おおすじ
ひとすじ
one bloodline
しんきん
heart muscle
みちすじ
path
しょうそくすじ
informed circles
せすじ
seam down the back (of clothing)