How risky is the explantation of a Medpor Chin Implant?

The removal of the implant is straightforward, albeit mildly traumatic to the tissues because of scar ingrowth into the material. The relevant issue is what will happen to the expanded soft tissue of the chin pad once it is removed. You should have a strategy for dealing with the excess soft tissue to avoid a sag of the chin tissues afterward.

The question of risk is not as important as how difficult would trying to remove this type of chin implant would be....

You are right that there are risks associated with the removal of the Medpor implant. I use Implantech silastic curvilinear or Conform implants because if they ever need to be removed for whatever reason they come out easily and safely. However Medpor has a tendency for tissue ingrowth so the removal involves much more dissection and tissue trauma and anxiety about possible nerve injury. As for collapsing of the empty capsule causing a bunching effect....I guess this is possible if a large defect was managed with a large implant and the subsequent dead space after removal is large....however with most medium or small implants this effect is not of any concern. However if you have persistent numbness and/or improper muscle action the implant should be removed and at a later date when the capsule has shrunk a new better sized implant can be reinserted. Whether renewed normal function will now take place at this late date is highly unlikely...but an improper implant should always be removed, problems only get worse as time goes on. There is an excellent surgical procedure to correct the sagging chin ( chin ptosis ) if this should be the case after removal

The risks involved with removal are lip/chin numbness, infection, bleeding; which were the same as putting it in.   They may be a little higher due to scar tissue and difficulty with removal of that type implant, but not with the proper surgeon.  One of the biggest risks is sagging of the chin soft tissues after removal.  If you do not want an implant, you may consider advancement genioplasty with the implant removal;  this would prevent the sagging problem.  Good luck.  Donald R. Nunn MD  Atlanta Plastic Surgeon