Couple things -
First - he threw 76.33 IP last year, which was his career high. You're supposed to bump by ~30% to avoid risk of injury, so that would put him at around 100 IP this year (99.33 IP to be exact).
Second - he likely won't be back until early to mid June, so he could be inserted into the rotation and give the Sox ~15 starts before he runs into an innings limit. Or, more likely, he throws about 35-40 IP out of the pen in long relief (adios, Mortensen), and picks up about 10 spot starts for DL stints and the such.