I have an ac joint separation of 12 mm how long until i can play rugby 100% again?

Depends: Non-operative approach to this would be 3 months or so. An operative approach may be even longer. Most would take non-operative approach and slow return to sports. Long-term success is high with non-operative approach.

Grade III AC injury : You describe what is called a grade iii AC separation. Either operative or nonoperative treatment may be indicated in such situations. Symptoms of local pain, swelling, and decreased motion should subside on the order of weeks to a month. Once motion and strength are reasonably back to normal, rugby play can resume. Reinjury or persistent pain that prevents a return o play may warrant surgery.

AC SEPARATION: Typically an AC JOINT separation can be treated conservatively when it is only a type 2 or 3. Treatment consists of therapy to regain motion after a short period in a sling. If pain persists or you have pain with activities then sometimes surgical intervention is warranted. Consult an Orthopaedic surgeon for a complete work up. Hope this information is helpful. Take care. Wilsonshoulder.com