Obesity and degenerative diseases like Osteoarthritis have a complex relationship. It is believed that overweight or obesity can act as both a trigger for osteoarthritis and a risk factor for the faster degeneration of the joint. Excess weight puts a greater pressure on a joint that is already undergoing damage due to Osteoarthritis, leading to a more rapid disease progression. When the disease progresses to a stage where all other conservative treatment options fail, a joint replacement surgery becomes inevitable.
Though any surgery comes with certain risks, increasingly, obesity itself is seen as a risk factor for higher complications and relatively poorer outcomes. While there are still differing views among leading Orthopedic surgeons on the level of emphasis given to Obesity as a risk factor, evidence from several studies has begun pointing that on a relative scale, obese patients have a higher postoperative complications risk rate. Further, the longevity of the replaced joint is also lower when compared to the normal weight patients.
As recently as December 2015, the American Association of Orthopedic Surgeons has qualified BMI as a factor for relatively poorer functional outcomes after TKA. Functional outcomes pertain to criteria such as those measured by the WOMAC index and measure outcomes such as pain sensation, mobility to name a few. It is important to clarify that the AAOS guidelines do not mention if Obesity also leads to a higher post-surgery complication rates.
Obesity Debate for TKA
The debate continues among the orthopedic surgeons on whether or not, Obesity poses any additional risks with regards to post-surgery complications.
A study carried out by the Department of Orthopaedic Surgery at New York-Presbyterian at Columbia University Medical Center tried to answer this question using an approach based on measuring the total surgery time. As few research studies have demonstrated that a longer surgery time is positively correlated with a higher post-surgery complications rate, this study aimed to analyze if obesity had any impact on the overall surgery time.
A cohort of 273 patients who underwent a primary TKA was classified into four groups as normal (18.5-24.9 KG/m2), overweight (25 – 29.9 KG/m2), obese class I (30 -34.9 KG/m2), obese class II (35-39.9 KG/m2) and obese class III (> 40 KG/m2). Here are some useful findings from the study.
- The average age of non-obese patients at the time of surgery was ~ 69 years whereas the average age for obese group patients was ~ 63 years. This finding indicates that the disease progression is quicker in obese patients as compared to the normal weight patients.
- Operative time increased for obese patients ranging from 105 to 114 minutes on average, compared to about 97 minutes for the normal group.
- Of the various types of post-surgery complications, skin or wound infection rate was higher for Obese Class II and Obese Class III patients, i.e. between 6% -7 % as compared to 4% for the normal group.
This study focused on assessing the early patient post-operative complications only, and not the overall long-term success rates. While no clear relationship has emerged about the impact of Obesity on immediate post-operative complications, except for a higher percentage of skin or wound infection, the effects of obesity on the long-term outcomes cannot be ignored.
Obesity and Long-Term Impact after TKA
Obesity may not directly lead to adverse outcomes, but in the event of any minor errors or misalignment in TKA, obesity results in much quicker degeneration of the replaced joint, creating a need for a quicker revision surgery.  A research published in Journal of Bone and Joint Surgery found that while failure rate for joint replacement was only 0.65% among normal weight patients, it was 2.5 times higher in obese patients (27 to 40 KG/m2) and almost 10 times greater in morbidly obese patients (>41 KG/m2) 
Given evidence such as above, a view is taking hold among few orthopaedic surgeons that obesity, and, in particular, morbid obesity can be considered a contra-indication for TKA, and if possible, measures should be taken to address the excess weight issue before conducting a TKA. News published in the Science Daily has even talked about a patient undergoing bariatric surgery to lose weight before undergoing a TKR.
Key takeaway for patients
As a patient, and especially if one belongs to an obese category, it is worthwhile to know that while obesity does not directly pose any immediate post-surgery risks that are significantly greater compared to normal weight patients, it may subsequently lead to outcomes that are not as good as others. Therefore, consulting with your surgeon about whether losing some weight before the surgery would be beneficial. It is also important for those who are diagnosed with early-stage Osteoarthritis to know that weight loss can reduce the rate of deterioration of your knee or hip joint.
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- Higher Body Mass Index Leads to Longer Operative Time in Total Knee Arthroplasty; Liabaud, Barthelemy; Patrick, David A.; Geller, Jeffrey A; The Journal of Arthroplasty, Volume 28 (4) – Apr 1, 2013
- Malposition and mal-orientation after total knee replacement, Tomoyuki Matsumoto and Ryosuke Kuroda
- Ritter Miller A, Kenneth E, Meding John B, Pierson Jeffrey L, Berend Michael E, Malinzak Robert A, The effect of alignment and BMI on failure of total knee replacement, Journal of Bone and Joint Surgery, Volume 93 (17) – Sep 7, 2011