Yes, METATARSI is a Scrabble word!

Letter values in Scrabble US: M 3, E 1, T 1, A 1, T 1, A 1, R 1, S 1, I 1.

Is it a valid word?

METATARSI is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the skeleton of the human foot between the toes and the tarsus; the corresponding part of the foot in birds or of the hind foot in quadrupeds