It is difficult to tell without a better idea of how severe the injuries were and any other injuries. Assuming he doesn't have any other serious injuries (neck, internal injuries etc) I would suspect he would be feeling fairly good in 6-12 weeks and within 3-6 months he would be "back to normal" as far as activities.
A LOT of it depends on his motivation to get better and cooperation with and effort he puts forth in rehabilitation (physical therapy)
This may be helpful
http://www.orthop.washington.edu/uw/tabID__3374/print__full/ItemID__153/mid__10326/Articles/Default.aspx
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