Around 312.9 million operations were carried out across the globe in 2012.
According to the World Health Organization (WHO), there were approximately 312.9 million operations carried out worldwide in 2012, increasing from 226.4 million in 2004.
It goes without saying that each and every one of these surgeries can improve or save a person's life, but there are some procedures that are so complex and unusual that they really bring home just how much surgery has progressed since the first heart transplant.
In this article, we take a look at five of the most bizarre and incredible surgical procedures to date.
1) Rotationplasty: Turning an ankle into a knee
Rotationplasty is an extraordinary form of reconstructive surgery that enables the ankle to be used as a knee joint.
The procedure involves the surgical removal of the bottom of the femur, the knee, and the upper tibia. The lower part of the leg is then rotated 180 degrees and attached to the thigh.
Put simply, the foot is attached to the knee backward. Once a prosthesis is fitted, the ankle of the foot functions as a knee.
The main aim of rotationplasty is to fully remove the tumor, but in a way that allows a child to have an active lifestyle, which would not be possible with complete amputation.
One amazing example of the procedure's success involves 14-year-old Gabi Shull from Missouri.
In the video below, Gabi explains how rotationplasty has changed her life:
At the age of 9, Gabi was diagnosed with osteosarcoma of the knee. The tumor was inoperable, and after 12 weeks of chemotherapy, Gabi and her parents decided on rotationplasty as the best treatment option.
"We talked about it with Gabi and we started looking at videos of kids roller blading, rock climbing, water skiing after having a rotationplasty," Gabi's mother Debbie told The Daily Mail earlier this year.
"We learned that there is absolutely no cons to rotationplasty except the way it looks and if you can get past that and focus on your quality of life then you've gained everything and have lost nothing," she added.
Just 1 year after the procedure, Gabi was able to walk again, and 2 years on, she is a competitive dancer. "The surgery has allowed me to do so much more than I expected and I would never go back and change it," she told The Daily Mail.
2) Osteo-odonto-keratoprosthesis: Restoring sight with a tooth
Often referred to as "tooth-in-eye" surgery, osteo-odonto-keratoprosthesis (OOKP) is just that - using a tooth to restore a patient's sight.
First described in the early 1960s by Prof. Benedetto Strampelli, of San Camillo Hospital in Italy, OOKP may be used for patients whose blindness is caused by irreversible damage to the cornea - the outer layer of the eye - and for whom other treatment methods have failed.
OOKP involves using a patient's tooth to restore vision.
The procedure involves the removal of a patient's canine or premolar tooth and the surrounding bone; the technique uses the patient's own tooth as the body is unlikely to reject it. A hole is then drilled in the tooth and a plastic lens is inserted.
The lens-tooth structure is then implanted into the patient's cheek, where it grows new blood vessels over a few months. The structure is then removed from the cheek and implanted into the eye. Light is able to travel through the lens, restoring the patient's vision.
In 2013, The Telegraph reported on a British man who regained his vision after undergoing OOKP.
In 1999, Ian Tibbetts lost hist sight completely through eye problems first triggered by an accident at work, whereby a piece of scrap metal struck his right eye and damaged his cornea.
In December 2012, Ian underwent OOKP at the Sussex Eye Hospital - the only hospital in the United Kingdom that performs the procedure - and was able to see his children clearly for the first time.
"I have my independence back now and I can start looking after the kids while my wife is out at work. Before, the kids were just shapes. I couldn't make them out," Ian told The Telegraph. "I had a picture in my head of what they looked like but they were better. I gave them a big hug and a kiss."
3) Hemispherectomy: Removing half of the brain to treat seizures
The brain is the most complex organ of the human body, containing billions of nerve cells that act as the command center for physical and psychological functions.
With this in mind, it seems beyond belief that removing half of the brain can be a feasible, effective surgical procedure for certain neurological conditions, but in some cases, it is. Such a procedure is known as hemispherectomy.
Hemispherectomy involves the partial or total removal or disconnection of one of the two hemispheres of the brain. It is considered a radical procedure, which can take as long as 12 hours to complete.
In hemispherectomy, one of the two hemispheres of the brain are removed or disconnected.
The procedure is usually performed on individuals who have neurological disorders that cause seizures on one side of the brain.
Such disorders include severe epilepsy, perinatal stroke, hemimegalencephaly (where one side of the brain is larger than the other), Sturge-Weber-Dimitri disease (characterized by facial birthmarks, glaucoma, and seizures), and Rasmussen's encephalitis (inflammation of the cerebral cortex).
According to The Hemispherectomy Foundation, hemispherectomy is most effective among children, as the remaining half of their brain can compensate for the some of the functions lost by removal of the other half.
Patients who undergo hemispherectomy will have some paralysis on the side of their body opposite to their removed hemisphere, and they normally lose sensation or function in the hands and fingers.
However, in many cases, the benefits of the surgery outweigh the risks and side effects.
One example of a successful hemispherectomy involves a 17-year-old girl called Karley Miller from Australia, who underwent the procedure to stop daily seizures caused by epilepsy. Her decision to have the radical operation was prompted by one seizure that lasted 9 ½ hours.
"I couldn't go anywhere without mum being a few steps behind, I couldn't even have a shower with the door locked in case I had a seizure and no-one could get to me," Karley told The Daily Mail earlier this year.
While Karley did experience some side effects from hemispherectomy, she no longer has seizures and is living a more happy, fulfilling life.
4) Heterotopic heart transplant: Two hearts may be better than one
Traditionally, a heart transplant involves removing a patient's damaged heart and replacing it with a healthy donor heart. This valuable procedure saves around 2,000 lives in the U.S. every year.
But what if a recipient's body is likely to reject a donor heart, or the donor heart is unable to function alone? This is where heterotopic heart transplantation may come in.
Heterotopic heart transplantation - also known as "piggyback" heart transplantation - involves implanting a healthy donor heart on the right side of the recipient's damaged heart. Both hearts are surgically attached, allowing blood from the damaged heart to flow into the new heart. The new heart can then pump blood around the body.
"Even though Mr. Smith was facing death, he could not have a standard heart transplant," explains Dr. Michael Madani, of the University of California-San Diego Sulpizio Cardiovascular Center.
"Removing the old heart and replacing it with a new heart would have caused the new heart to fail, because resistance to flow in his lungs - called pulmonary hypertension - was so high. But together, the two hearts share the work and get the job done," he added.
5) Head transplant: A possible cure for paralysis
In 2013, Italian neurosurgeon Dr. Sergio Canavero announced proposals to perform the world's first ever human head transplant - a procedure he believes has the potential to treat paralysis caused by neurological or muscle-wasting diseases.
The procedure - named HEAVEN-GEMINI - will involve removing the heads of the recipient and a healthy donor using an "ultra-sharp blade," in order to avoid spinal cord damage.
The world's first human head transplant is set to take place in December 2017.
The recipient's head and the donor body will then be placed into deep hypothermia for around 45 minutes to reduce nerve damage. The recipient's head will then be attached to the donor body using spinal cord fusion.
All in all, the operation is expected to take around 36 hours and $11 million to complete, and it will require the skills of around 150 surgeons and nurses.
After the procedure is complete, the recipient will be kept in a coma for 3-4 weeks, in order to minimize movement and ensure the nerve connections between the neck and the spine have time to fuse together.
While this extreme procedure might sound like the makings of science fiction, it is set to become a reality. In October last year, Dr. Canavero told Medical News Today that the first human head transplant will be performed in December 2017.
A number of individuals have already volunteered to have the procedure, including Valery Spiridonov, a 31-year-old man from Russia who has a muscle-wasting condition called Werdnig-Hoffman disease, which has left him paralyzed from the neck down.
Unsurprisingly, the prospect of the first human head transplant has been met with much criticism, but Dr. Canavero is confident the procedure will be a triumph.
"It will be a success," he told MNT. "There is a detailed plan - we are not just concocting this in some secret Frankenstein lab. We are way ahead now into the project, everything is moving - it is no longer science fiction."