Another Reason to Keep the Weight Off: Knee Pain and the Risk of Surgery

Aaron Litz, National Center for Health Research

It seems like the list of health risks linked to obesity keeps growing.  A 2013 study of thousands of people with artificial hips or knees has found that men and women who had their knees replaced before age 65 were much more likely to be obese than older people getting that same surgery.[1] When it comes to knees giving out or having problems, it turns out that excess weight is just as bad as or maybe worse than getting older.

While surgeries for first-time knee replacement doubled in less than ten years (from 313,618 in 2001[2] to more than 620,000 in 2009[3]), they tripled among people 45 to 64. Experts believe that obesity is a major reason for the increase in this age group.

In the 2013 study of 9,000 men and women with knee replacements, 55% of the patients under 65 were obese (with a BMI of 30 or higher) compared to 43% of the patients 65 and over. The younger knee replacement patients were also twice as likely to be “morbidly obese,” which is the term for obesity that is the greatest threat to health (BMI over 40): 11% vs. 5% of the older patients. As expected, given the impact of obesity on knee damage, both groups are more likely to be obese than people of the same age who do not need knee replacement surgery. In comparison, knee replacement patients ages 65 and over are only slightly more obese than their age group in the general population (43% and approximately 40%, respectively), and knee patients ages 45-64 are considerably more obese than their age group in the general population (55% and 36%).[4]

How does being overweight hurt the knees?

Extra pounds stress our knees in three different ways:

  • Mechanical stress: the constant stress of excess weight makes the joints work harder and causes strain. Although “weight-bearing exercise,” such as walking and lifting weights, helps strengthen bones, carrying extra weight throughout your body is harmful.
  • Biomechanical stress: The excess weight puts pressure on cells in the knee joint that are supposed to send out signals to the body for cell growth. With the excess weight, these cells do not send out the right signals, and cells in the knee joint do not get repaired.[5]
  • Fat is not just stored energy sitting in the body waiting to be used; it also communicates with the body. For instance, fatty (adipose) tissue sends out messages that affect the way the body functions.[6] Cell-signaling proteins, called adipokines, slow down blood vessel growth, causing knee joints to deteriorate and be painful.

When fat takes its toll, the cartilage on the end of our bones wears away leaving bone to scrape against bone. This kind of wear-and-tear is called osteoarthritis, which is different from rheumatoid arthritis. Patients who develop osteoarthritis in their knees find that walking and most forms of exercise (other than swimming) become increasingly painful. As a result, they become less active and put on more weight, which causes their knee joints to deteriorate more! It’s a vicious cycle, so it’s no wonder that patients with osteoarthritis report a lower quality of life,[7] and obese patients even more so,[8] leading their doctors to recommend knee surgery.

Coping with pain and delaying surgery 

So, if you’re overweight and starting to experience knee problems, what are some things you can do to improve your “knee health” and delay knee surgery?

Shed some pounds. Losing weight can make a big difference.  In a study of 399 men and women, a 10% decrease in weight helped people have less knee pain, and the more weight they lost, the less pain they had.[9] Small changes in diet and exercise were the best ways to lose weight, and reduce pain.  The people who felt less pain reported a better quality of life.

Exercise Therapy. Some studies show exercise therapy helps reduce knee pain, but other studies show it has no effect.  Resistance exercise, where people lift or push weights, helps strengthen and regrow muscles and cartilage around the knee.[10] Besides being able to move better, patients with stronger muscles and cartilage around the knee feel less pain. Some studies suggest that walking is just as helpful as resistance exercise.[11] It is not clear what types of exercise are most effective, or whether exercise in the water are more effective than those on land. In the absence of clear proof of what works best, adopt an exercise plan that helps you reduce pain and, if possible, lose weight.

When researchers reviewed over 130 studies comparing home-based exercise to center-based exercise, they found that although the knees of both groups improved, the people in the center-based group were twice as likely to stick with their exercise plan.[12] The researchers suggest that even a few visits to a fitness center mixed in with a home-based exercise plan can help patients stay on track. You may not need a personal trainer or fitness club — a group of friends at a community center or local gym can help keep you following your recommended exercise plan.

What about Supplements like Glucosamine and Chondrotin?

A well designed study of the dietary supplements glucosamine and chondroitin, funded by the U.S. government, found that the supplements did not provide pain relief or slow the loss of cartilage, whether the two ingredients were in one combination pill or in separate pills.[13] But, to the researchers’ great surprise, participants did unusually well on placebo, far better than in other studies!  While the supplements were no better than placebo, it is difficult to ignore the fact that both the placebo and the supplement group did better than expected.  In addition, there was a small group of patients with moderate to severe knee pain who had a statistically significant reduction in pain when they took glucosamine and chondroitin daily, compared to placebo.[14] Unfortunately, the number who benefited was too small for researchers to figure out how they were different from other patients (male, female, young, old, overweight or not, etc.). So, while it is impossible to be enthusiastic about the benefits of these supplements, they do no harm and possibly they might do some good.  In the study, participants took their 1500 mgs of glucosamine a day in 3 doses of 500 mgs and their 1200 mgs of chondroitin sulfate in 3 doses of 400 mgs.[13]

Knee Replacement Surgery 

When you can no longer get around without pain, and exercise and dieting hasn’t helped, it’s time for knee replacement surgery, which is called total knee arthroplasty (TKA). A surgeon attaches a new joint to the ends of the bones that are grinding against each other. The new joint has two parts that fit together and are supposed to glide like a healthy knee joint. Typically, patients need six weeks of recovery before walking again, and many months before their muscle strength returns.

In 2010, there were 719,000 knee replacement surgeries in the U.S.[15] By 2030 that number is expected to rise to about 3.4 million![16] A little less than half of the knee replacement surgeries (334,000) done in 2010 were on people under 65. An estimated 10% of the 719,000 knee replacements were revision surgeries—operations to fix complications from a previous knee surgery, or to replace knee implants that had worn out? Interestingly, most of the revision surgery is being performed on people under 65[17][18]

While some medical centers claim that most knee replacements last for 20 years,[19] we don’t actually know how long artificial knees last So far, the longest any study has followed knee surgery patients for is 10 years,[20] and most studies have only followed patients for 5 years after surgery.[21] And, since implant companies frequently make changes to their knees, it is impossible to know if the knee you get today will last as long as similar knee joints sold 10 years ago.  We do know, however, that while some knee implants last 20 years, some require a second surgery much sooner—sometimes within a year.[22]

Some of the reasons for revision knee surgery include:[23] [24]

Infection: The new joint is a foreign object in the body with spaces where infections can grow. Knee revision is sometimes needed to clean the area and prevent the infection from spreading. Infections account for about 25% of all revision surgery

Instability: Sometimes the body’s soft tissue can’t get a strong hold on the joint, making it hard to control joint movements. Instability can also be caused from mechanical loosening of the joint. This accounts for about 12% of all revisions, and occurs when the joint parts do not fit together correctly.

Aseptic loosening happens when particle debris from the artificial joint flakes off.  The debris can be from the metal or the plastic of the artificial joint; either way, the body may respond to these foreign particles with protector and fighter cells. The cells loosen the connection that the artificial joint makes with the body’s bones and tissues.

Most people think that once they have their knees replaced they are “done,” and won’t have to deal with knee problems for a long time or maybe ever again. Unfortunately, artificial knees don’t come with warranties or guarantees: not one manufacturer of artificial knees refunds the patient or insurance company when the knee fails or pays for the needed revision surgery.[25]

More Knee Surgery Means More Problems

The younger a person is when she gets her knee(s) replaced, the more likely she is to need additional knee surgeries in her lifetime.[26] Each consecutive surgery becomes more difficult and the recovery time longer, as more and more of the body’s original tissue and bone are damaged. With the first surgery, a surgeon tries to attach the joint to tissue and bone within the body for stability. In revision surgery, a surgeon must go back in and remove scar tissue and other debris that may be causing pain. After “cleaning up” from the first surgery, a surgeon can begin to replace the non-working joint with a new joint. Each time a surgeon goes back into the body, more damage occurs to the area surrounding the joint, as more bone and tissue are removed. Undergoing repeat surgeries isn’t easy for anyone, but it’s particularly difficult for someone who is very overweight and possibly diabetic or with heart problems as a result.

The Bottom Line

If you are overweight or obese and have knee pain, changes in diet and exercise can reduce your pain and help you avoid or delay surgery. Surgery is not a “quick fix,” so delay it if you can do so in a healthy way.  Remember that extra pounds mean extra stress on the knees, whether they are the knees you were born with or artificial ones.  Even after knee replacement, being overweight or inactive will cause problems that will result in needing more surgery sooner than you otherwise would – and that subsequent surgery is likely to be worse than the original knee replacement.

All articles on our website have been approved by Dr. Diana Zuckerman and other senior staff. 

  1. Franklin P, Ayers DC, et al. 2013. Findings from FORCE-TJR database. http://www.umassmed.edu/news/2013/research/increasing-rate-of-knee-replacements.aspx Presented at American College of Rheumatology and the Association of Rheumatology Health Professionals meeting on October 30, 2013.
  2. Kim, S. (2008), Changes in surgical loads and economic burden of hip and knee replacements in the US: 1997–2004. Arthritis & Rheumatism, 59: 481–488. doi: 10.1002/art.23525
  3. Weinstein AM, Rome BN, Reichmann WM. 2013. Estimating the burden of total knee replacement in the United States. : J Bone Joint Surg Am. 2013 Mar 6;95(5):385-92. doi: 10.2106/JBJS.L.00206.]
  4. Cynthia L. Ogden, Margaret D. Carroll, Brian K. Kit. 2012. Prevalence of Obesity in the United States, 2009–2010. NCHS Data Brief, Number 82. http://www.cdc.gov/nchs/data/databriefs/db82.pdf
  5. Millward-Sadler SJ, Salter DM. Integrin-dependent signal cascades in chondrocyte mechanotransduction. Ann Biomed Eng2004;32:435–46.
  6. P Pottie, N Presle, B Terlain. 2006. Obesity and osteoarthritis: more complex than predicted! Ann Rheum Dis 2006;65:1403-1405 doi:10.1136/ard.2006.061994 http://ard.bmj.com/content/65/11/1403.full
  7. Lawrence RC, Felson DT, Helmick CG, et al; National Arthritis Data Workgroup. Estimates of the prevalence of arthritis and other rheumatic conditions in the United States: part II. Arthritis Rheum. 2008;58(1):26-35.
  8. Elena Losina, PhD Impact of Obesity and Knee Osteoarthritis on Morbidity and Mortality in Older Americans Ann Intern Med. 2011;154(4):217-226. doi:10.7326/0003-4819-154-4-201102150-00001 Substantial loss of quality life-years from obesity and knee OA
  9. Messier SP, Mihalko SL, Legault C, et al. Effects of Intensive Diet and Exercise on Knee Joint Loads, Inflammation, and Clinical Outcomes Among Overweight and Obese Adults With Knee Osteoarthritis: The IDEA Randomized Clinical Trial. JAMA. 2013;310(12):1263-1273. doi:10.1001/jama.2013.277669
  10. Kevin R. Vincent, MD, PhD and Heather K. Vincent, PhD. 2012. Resistance Exercise for Knee Osteoarthritis. PM & R : the journal of injury, function, and rehabilitation 1 May 2012 volume 4 issue 5 Pages S45-S52 DOI: 10.1016/j.pmrj.2012.01.019
  11. Messier S, Loeser R, Miller G, et al. Exercise and dietary weight loss in overweight and obese older adults with knee osteoarthritis. Arthritis Rheum 2004;50(5):1501–10.
  12. Gail D Deyle, Stephen C Allison, Robert L Matekel. 2005. Physical Therapy Treatment Effectiveness for Osteoarthritis of the Knee: A Randomized Comparison of Supervised Clinical Exercise and Manual Therapy Procedures Versus a Home Exercise Program. Physical Therapy December 2005 vol. 85 no. 12 1301-1317
  13. Sawitzke AD, Shi H, Finco MF. 2010. Clinical efficacy and safety of glucosamine, chondroitin sulphate, their combination, celecoxib or placebo taken to treat osteoarthritis of the knee: 2-year results from GAIT. Ann Rheum Dis. 2010 Aug;69(8):1459-64. doi: 10.1136/ard.2009.120469. Epub 2010 Jun 4.
  14. Daniel O. Clegg, M.D., Domenic J. Reda, Ph.D. 2006. Glucosamine, Chondroitin Sulfate, and the Two in Combination for Painful Knee Osteoarthritis. N Engl J Med 2006; 354:795-808February 23, 2006DOI: 10.1056/NEJMoa052771
  15. CDC, National Center for Health Statistics. 2010. Number of all-listed procedures for discharges from short-stay hospitals, by procedure category and age: United States, 2010 http://www.cdc.gov/nchs/data/nhds/4procedures/2010pro4_numberprocedureage.pdf
  16. Kurtz S, Ong K, Lau E, Mowat F, Halpern M. 2007. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am. 2007 Apr;89(4):780-5.
  17. Kevin J. Bozic, MD, MBA, Steven M. Kurtz, PhD, Edmund Lau, MS. 2009. The Epidemiology of Revision Total Knee Arthroplasty in the United States. Published online 2009 June 25. doi: 10.1007/s11999-009-0945-0. Clin Orthop Relat Res. 2010 January; 468(1): 45–51.
  18. Steven M. Kurtz, PhD,1 Edmund Lau, MS,1 Kevin Ong, PhD. 2009. Future Young Patient Demand for Primary and Revision Joint Replacement: National Projections from 2010 to 2030. Clin Orthop Relat Res. 2009 October; 467(10): 2606–2612. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2745453/#!po=35.7143
  19. Cleveland Clinic, Orthopedic and Rheumatologic Institute. 2013. Total Knee Replacement. http://my.clevelandclinic.org/orthopaedics-rheumatology/treatments-procedures/hic-total-knee-replacement-surgery.aspx
  20. Diduch DR, Insall JN, Scott WN. 1997. Total knee replacement in young, active patients. Long-term follow-up and functional outcome. J Bone Joint Surg Am. 1997 Apr;79(4):575-82. http://www.ncbi.nlm.nih.gov/pubmed/9111404
  21. Baker P, Jameson S, Critchley R. 2013. Center and surgeon volume influence the revision rate following unicondylar knee replacement: an analysis of 23,400 medial cemented unicondylar knee replacements. J Bone Joint Surg Am. 2013 Apr 17;95(8):702-9. doi: 10.2106/JBJS.L.00520.http://www.ncbi.nlm.nih.gov/pubmed/23595068
  22. David Culliford, Joe Maskell, Andy Judge 2013. A population-based survival analysis describing the association of body mass index on time to revision for total hip and knee replacements: results from the UK general practice research database. BMJ Open 2013;3:e003614 doi:10.1136/bmjopen-2013-003614
  23. Kevin J. Bozic, MD, MBA, Steven M. Kurtz, PhD, Edmund Lau, MS. 2010. The Epidemiology of Revision Total Knee Arthroplasty in the United States. Clin Orthop Relat Res. 2010 January; 468(1): 45–51.http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2795838/
  24. end Kevin J. Bozic, MD, MBA, Steven M. Kurtz, PhD, Edmund Lau, MS. 2010. The Epidemiology of Revision Total Knee Arthroplasty in the United States. Clin Orthop Relat Res. 2010 January; 468(1): 45–51.http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2795838/
  25. Lisa McGiffert, Safe Patient Project. Sample letter sent to CEO’s of the 6 top volume hip and knee implant makers: Biomet, DePuy, Smith & Nephew, Stryker, Wright Technologies and Zimmer. https://secure.consumersunion.org/site/SPageNavigator/SPP_medicaldevice_CEOletter.html
  26. Kurtz SM, Lau E, Ong K, Zhao K, Kelly M, Bozic KJ. Future young patient demand for primary and revision joint replacement: national projections from 2010 to 2030. Clin Orthop Relat Res. 2009 Oct; 467(10):2606-12.