There are many studies proving the powerful connection between our thoughts, our physical body, and how one can help the other heal. Hypnosis is a powerful way of thinking these thoughts.
If the experiencing part of your brain is led to a place where it can super focus in the very details of a healing process, it can actually create that process, part of it, or a different process with a similar outcome. It is called placebo. The opposite is true as well; thinking repeated and super focused negative thoughts in detail can lead to just that, or something aligned with it.
Learning about hypnosis is learning how the painter, director and script writer in your subconscious works, and training them.
Here is a study about "knee surgery" to inspire you.
Many patients report symptomatic relief after undergoing arthroscopy of the knee for osteoarthritis, but it is unclear how the procedure achieves this result. We conducted a randomized, placebo-controlled trial to evaluate the efficacy of arthroscopy for osteoarthritis of the knee.
A total of 180 patients with osteoarthritis of the knee were randomly assigned to receive arthroscopic débridement, arthroscopic lavage, or placebo surgery. Patients in the placebo group received skin incisions and underwent a simulated débridement without insertion of the arthroscope. Patients and assessors of outcome were blinded to the treatment-group assignment. Outcomes were assessed at multiple points over a 24-month period with the use of five self-reported scores--three on scales for pain and two on scales for function--and one objective test of walking and stair climbing. A total of 165 patients completed the trial.
At no point did either of the intervention groups report less pain or better function than the placebo group.