In July 2009, Yoshiki had surgery on his continuing neck problems, of which his doctor claimed he is still steadily recovering from. However, he still has numbness on his left hand and therefore he had an epidural injection on the morning of May 27th(local time) at Cedars-Sinai Medical Center in L.A. The procedure was successful and he is doing well. X JAPAN will appear at Lollapalooza and Yokohama as scheduled.

You can find more information about the procedure on YOSHIKI's website.
More information around the topic you can find on Wikipedia for instance.

Sources: TV Asahi, Oricon, Yahoo, Sanspo