The Chunichi Dragons announced today that Toshiya Okada had surgery on his left hand (血管外膜剥離術) at a hospital in Gunma.
[UPDATE 6/14 @ 1:32am]
Okada was discharged from the hospital on June 9 with a cast. He will have to wear the cast for one to two weeks. He began his rehab on June 10. He might be ready to begin throwing some time in August.
Source: Sponichi 6/13/2017