Same pain relief for both the obese and normal weight after joint replacement

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A University of Massachusetts Medical School study finds that obese patients who underwent knee or hip replacement surgery reported virtually the same pain relief and improved function as normal-weight joint replacement patients six months after surgery.

“Our data shows it’s not necessary to ask patients to lose weight prior to surgery,” said Dr Wenjun Li, associate professor of medicine and lead author on the study. “It’s challenging for a patient who is severely overweight and suffering in pain to exercise – often they just can’t do it. Our evidence showed that severe morbidly obese patients can benefit almost equally as normal weight patients in pain relief and gains in physical function.”

The aim of the study was to evaluate the extent of pain relief and functional improvement in total joint replacement patients with various levels of obesity. The researchers concluded that while obesity is associated with a greater risk of early complications, obesity in itself should not be a deterrent to undergoing total joint replacement to relieve symptoms.

Prior research has documented that obesity is associated with a small, but increased likelihood of infection after total knee replacement, which may discourage obese patients from having surgery. “However, in this paper we report that obese patients have comparable pain relief and functional outcomes after surgery,” said Dr Patricia Franklin, professor of orthopedics & physical rehabilitation. “Patients should know that these benefits may outweigh risks.”

Franklin is principal investigator of the Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement (FORCE-TJR) programme from the US Agency for Healthcare Research and Quality. She co-authored the paper with Dr David Ayers, the Arthur M Pappas chair in orthopedics and chair and professor of orthopedics & physical rehabilitation; Dr Jeroan J Allison, vice chair and professor of quantitative health sciences; and colleagues at Hartford Hospital and Geisinger Health Centre.

Preoperative and 6-month post-operative data on function, joint pain and body mass index (BMI) from a national sample of 2,040 patients who had undergone total hip replacement and 2,964 who had undergone total knee replacement from May 2011 to March 2013 was collected. Pre-operative and post-operative function and pain were evaluated according to BMI status, defined as under or of normal weight, overweight, obese, severely obese, or morbidly obese. A greater obesity level was associated with worse pain at baseline but greater post-operative pain relief, with average post-operative pain scores at six months similar across the BMI levels.

“This surprised us a little bit. Past analysis showed that obesity is associated with outcomes to some degree, but here we see the magnitude is so small it won’t make much difference, and severely obese patients can benefit a lot from the surgery,” said Li. “Patients who can lose weight should, but we acknowledge many people can’t, or it will take a long time during which their joints will worsen. If they can get the surgery earlier, once function is restored they can better address obesity.”

“Losing weight by making appropriate dietary changes and increasing the calories burned each day through water exercise programmes and other aerobic, non-weight bearing activities is always appropriate to decrease the risk of complications for overweight patients,” said FORCE-TJR co-investigator Ayers. “This manuscript adds to our collective knowledge regarding the risk benefit ratio of total joint replacement surgery in obese patients. The debate will continue in the morbidly obese patients with BMI over 40, and the super obese with a BMI over 50, regarding what steps can and should be taken to lower the risks before these elective surgical procedures.”

Funded by a $12m grant, the FORCE-TJR research programme has developed a national database of surgical results and patient-reported outcomes from more than 30,000 patients. FORCE-TJR is unique in quantifying patient reported pain and function after surgery in order to assess multiple factors associated with the best results.

“Other registries primarily evaluate implant longevity,” said Franklin. “Thus FORCE-TJR has taken the lead in evaluating patient factors and outcomes.”

Abstract
Background: Obesity has been associated with lower function and more pain before and after total hip or knee replacement (THR or TKR). We examined the changes between preoperative and postoperative function and pain in a large representative U.S. cohort to determine if there was a relationship to obesity status.
Methods: Preoperative and 6-month postoperative data on function (Short Form-36 Physical Component Summary [PCS] score), joint pain (Hip disability and Osteoarthritis Outcome Score and Knee injury and Osteoarthritis Outcome Score), and body mass index (BMI) were collected from a national sample of 2,040 patients who had undergone THR and 2,964 who had undergone TKR from May 2011 to March 2013. Preoperative and postoperative function and pain were evaluated according to BMI status, defined as under or of normal weight, overweight, obese, severely obese, or morbidly obese.
Results: Patients undergoing THR were an average of 65 years of age; 59% were women, 94% were white, and 14% were severely or morbidly obese. A greater obesity level was associated with a lower (worse) PCS score at baseline and 6 months postoperatively. Severely and morbidly obese patients had less postoperative functional gain than the other BMI groups. A greater obesity level was associated with more pain at baseline but greater postoperative pain relief, so the average postoperative pain scores did not differ significantly according to BMI status. Patients undergoing TKR had an average age of 69 years; 61% were women, 93% were white, and 25% were severely or morbidly obese. A greater obesity level was associated with a lower PCS score at baseline and 6 months. The postoperative gain in PCS score did not differ by BMI level. A greater obesity level was associated with worse pain at baseline but greater pain relief at 6 months, so the average pain scores at 6 month were similar across the BMI levels.
Conclusions: Six months after total joint replacement (TJR), severely or morbidly obese patients reported excellent pain relief and substantial functional gain that was similar to the findings in other patients. While obesity is associated with a greater risk of early complications, obesity in itself should not be a deterrent to undergoing TJR to relieve symptoms.

Authors
Li W, Ayers DC, Lewis CG, Bowen TR, Allison JJ, Franklin PD

University of Massachusetts Medical School material
Journal of Bone and Joint Surgery abstract


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