Obesity and Joint Replacement Surgery
Obesity is major problem facing our affluent society. In 2014-2015, a staggering 63.4 percent of Australian adults were overweight or obese -- well over half of our nation's population. That's almost two in three adults. This is an increase from 1995, which was 56.3 percent, illustrating that the problem is getting worse.
Orthopaedic surgery deals with the treatment of Joints and Bone predominantly. In the last 30yrs major advances have taken place in the field of major Joint replacement, Namely the Hip, Knee and the Shoulder. As far as the Hip and Knee go the major function is to bear weight and allow ambulation. 
The Surfaces of the joint is covered by a soft, very smooth gristle called Cartilage. This cartilage has very durable wear characteristics but unfortunately does not have the capacity to regenerate like other tissues in the body. In most large joint the cartilage sits in a bed of avascular matrix. In the Hip and Knee the cartilage type is called hyaline. Once this cartilage starts to wear it gets replaced by Fibro-Cartilage which does not share the same were characteristic as Hyaline.
The cartilage wear is a product of force (load) over time and also amount of work done (movement) over time. If you work very hard loading your knees with heavy loads your cartilage will wear over time. Now take obesity into this equation and you will find that the amount of work done may stay the same or decrease but as the load increases the wear rate will increase and lead to total loss of cartilage. This is call arthritis.
Osteoarthrits is the most common reason for Hip and Knee Replacements in the world. There are obviously other factors that come into play when looking at arthritis in the general population eg , Knee Trauma, Hereditary factors, Previous Surgery, Inflammatory conditions like Rheumatoid, etc etc. However unfortunately some of these factors we may not be able to control . However Obesity is definitely a factor that is totally under our control. There is no doubt that if you carry excess weight on your lower limbs for a prolonged period to time you will cause cartilage wear leading to Arthritis which may require replacement Surgery.
Attached is a link to an article written by an orthopaedic surgeon summarising the effects of obesity on orthopaedic surgery and the preoperative complication. Unfortunately Bariatric Surgery is not available in the Public Health Sector and i m aware that the out of pocket expanses can be prohibitive for a lot of obese patients who have failed conventional weight loss methods.