Hello! I Recently Had Wrist Surgery To Repair My Ligaments

Hello! I recently had wrist surgery to repair my ligaments in my right wrist, as well as a dislocated ulna. The injury happened last April and the surgery was in September. Since then I have been doing physio and have gained back up and down movement and side to side. However I cannot flip my wrist over from the pronation position to the supine position. The surgeon indicated that I would have to go back for another surgery if I could not do that movement as I am only 20. I am just looking for some clarification as to what has happened to my wrist as well as maybe how the next surgery would help me.

Thank You