Not sure what is "extreme invasive knee surgery", it's not a medical term to my knowledge. Typically comparisons are made between "open" knee surgery (surgery made by making an incision, exposing the affected area, which in this case is the knee joint) and arthroscopic surgery (a series of several small incisions made to allow the passage of an arthroscopic camera as well as a variety of instruments/trocars to manipulate/sculpt/cauterize/suture the affected joint.
There will be many comparisons in the medical literature on those. You need to narrow your focus to a particular injury and the surgery performed to repair it. For instance, an ACL (anterior cruciate ligament) tear, medial meniscus injury, medial collateral ligament injury (MCL), etc...
Once you picked the particular injury, you need to look into what are considered endpoints for recovery (time in rehab, return to original function, pain-free range of motion (a nice quantitative indicator), to name just a few.
Medical searches are most commonly performed by physicians using Medline searches. A free portal can be found at:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed
These searches are not designed for non-medical professionals, so portions of that will be using anatomical/physiological terms that you may not be familiar with (hence the first two years of torture in medical school learning them). Looking these up in an online medical dictionary should help.
Be very wary of the miriad of online posts which are nothing more than ads for rehab centers, orthopedic practices, chiropracters, Aunt Tillies magic knee fixer-upper, etc... You are looking for research in peer-reviewed journals. Lacking that, it may very well be useless propaganda.
Google searches, answers.com, etc... can be a starting point to learn terms and types of surgery, but you are really looking for review articles in Orthopedic Surgery journals.
Good luck. I hope this is for a science fair project, not for an injured knee.
