What are the known risks of breast reconstruction?

Depends on Method. The two types of reconstruction are "flap" procedures, where tissue is transferred from the abdomen or back to the chest, or implants. Both have low risks of bleeding, infection, fluid build-up, etc. The flap procedure runs the small risk of failure; the implants can cause hardening around the capsule or even rupture. In general, these are low-risk procedures in healthy women.
Risks. The risks of flaps and implants are similar, bleeding, infection, numbness, pain, scarring, asymmetry, fluid collections, wound breakdown, need for further operation, injury to underlying structures. With implants, there is also the risk of rupture and capsular contracture. This is a discussion that must be had with you plastic surgeon prior to any operation so that you are informed.
Reconstruction risks. The risks of reconstruction (specifically implants), are infection, collections of blood or fluid, implant failure, wound healing problems, skin flap circulation problems, reaction to either the implants or skin substitute (i.e. Allograft), asymmetry, scarring, or need for further surgery. By knowing the possible risks, your surgeon is better prepared to avoid them.
Reconstruction Risks. The risks of breast reconstruction include bleeding, infection, wound separation, scar, hematoma, seroma, altered sensation, loss of tissue or implants, flap loss, donor site complications, implant rupture, capsular contracture, displacement, asymmetry, dissatisfaction with your cosmetic result, and need for revision in the future. Your board certified plastic surgeon should review these carefully.
Reconstruction. The risks of each surgery are general interns of skin infections, bleeding in the surgical site, fluid build up in surgical site(s) and scarring. Each technique used has different concerns. In fat grafting you are more worried about how much fat survives. With implants it is infection and scarring. With flaps it is a rare blood vessel problem that leads to partial or total loss.
Not that risky. Biggest risk is infection which in the past usually required implant removal but w recent techniques can usu be salvaged. These techniques have also markedly decreased the risk of capsular contracture.Fewer are doing flaps which have distinct own risks. Most complic'ns can be worked thru so the most significant would've the pr disappointed in result. Too much to answer herein.
Depends on procedure. There are general risks and risks that are specific to the type of reconstruction. General risks include failure of the reconstruction, infection, bleeding, changes in sensation, asymmetry, blood clots, ugly scarring, dissatisfaction with the cosmetic results and need for more procedures. Implant reconstruction is also associated with hardening, rippling, rupture, and need for implant replacement.