This column is written by medical students and is dedicated to reviewing the science behind obesity and bariatric surgery.
Column Editor: Daniel B. Jones, MD, MS, FASMBS Professor of Surgery, Harvard Medical School Vice Chair, Beth Israel Deaconess Medical Center Boston, Massachusetts
This month: The Effects of Weight Loss and Bariatric Surgery on Knee Osteoarthritis
by Brian W. Yang
Medical Student, Harvard Medical School Boston, Massachusetts
Bariatric Times. 2017;14(2):18–20.
Knee osteoarthritis (OA) is an important cause of morbidity in the United States. One of the most significant risk factors for osteoarthritis is obesity. Both nonoperative weight loss management and weight loss surgeries, including the Roux-en-Y gastric bypass, adjustable gastric band, and others have been demonstrated to improve knee pain, function, and biomechanics in individuals with obesity. This column reviews the current medical literature underlying the roles that nonoperative weight loss and operative weight loss surgery play in the improvement of knee osteoarthritis symptoms.
Osteoarthritis is the most common type of joint disorder in the United States, caused by the progressive mechanical wear of cartilage within the joint space.1 In the knee, this leads to pain, swelling, and decreased function. More than half of adults in the United States diagnosed with knee osteoarthritis will have severe pain that fails nonsurgical treatment and subsequently require a total knee replacement. Risk factors for knee osteoarthritis include advanced age, female gender, repetitive joint injury, joint malalignment, and chronic knee laxity. However, one of the most significant modifiable risk factors for osteoarthritis is obesity., In a recent meta-analysis, a five-unit increase in body mass index (BMI) was associated with a 35-percent increased risk of knee osteoarthritis.
Increased weight places mechanical increased strain on the knee joint. Data have shown that each pound of weight lost corresponds to a four-fold reduction in force applied to the knee joint. However, mechanisms underlying the connection between weight and osteoarthritis are still varied, including changes in cartilage structure, increased knee joint load,,, and knee joint space narrowing., When considered in combination, models suggest that persons aged 50 to 84 lose 10 to 25 percent of their remaining quality-adjusted life expectancy due to knee osteoarthritis and/or obesity, with Hispanic and black women showing disproportionately high losses. Furthermore, weight loss has been associated with increased longevity of primary total knee replacements, improved functional scores after total knee replacement, and decreased rates of total knee replacement revision.[11–13] Bariatric surgery prior to total knee replacement has also been associated with fewer postoperative complications.
Bariatric weight loss surgery has been demonstrated to improve multiple comorbidities associated with obesity, including hypertension, hyperlipidemia, diabetes, and gastroesophageal reflux disease. This article reviews the literature assessing the effects of nonoperative weight loss on knee osteoarthritis and, more specifically, the role that weight loss surgery plays in the improvement of knee osteoarthritis symptoms.
Nonoperative weight loss and its effects on knee osteoarthritis
Several randomized control trials have evaluated the effects of nonoperative weight loss on the symptoms and effects of knee osteoarthritis. In the randomized Arthritis, Diet, and Activity Promotion Trial (ADAPT), Messier et al studied 316 adults with overweight and obesity with knee osteoarthritis to determine if exercise and dietary weight loss, either in combination or separate, was more effective than a healthy lifestyle control group in improving self-reported knee physical function as measured by the western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Results showed that diet and exercise combined resulted in statistically significant improvements in WOMAC self-reported physical function, distance walked in six minutes, stair-climb time, and WOMAC knee pain scores. However, the diet only group did not show any significant differences when compared to the healthy lifestyle controls and the exercise only group only showed an improvement in distance walked in six minutes.
In a more recent study, Christensen et al assessed the effects of weight reduction through a low-energy diet on the symptoms of knee osteoarthritis. Eighty patients with BMIs ranging from 35.9 to 62.6kg/m2 were randomized into either a low-energy diet group or control diet group, with the WOMAC index used to measure the effects on knee osteoarthritis symptoms. Results showed that a weight reduction of 10 percent improved knee function by 28 percent. Interestingly, reduction in body fat percent was shown to be the best predictor of change in WOMAC index, with every percent of body fat reduced corresponding to a 9.4-percent improvement in WOMAC. This relationship between body fat percentage and knee osteoarthritis relief is corroborated by a randomized control trial by Toda et al. In their study, 22 patients with knee osteoarthritis and a BMI over 26.4kg/m2 were treated with a low calorie diet, appetite suppressant, and nonsteroidal antiinflammatory drugs (NSAIDs) for six weeks. Data showed a significant correlation between reduction in body fat as well as number of steps per day with decreases in knee osteoarthritis symptoms. Remarkably, weight loss was not independently correlated with symptomatic relief of knee osteoarthritis in their study. Finally, in a randomized control trial of 24 participants with overweight/obesity with radiographic evidence of knee osteoarthritis comparing exercise and diet against exercise alone, both exercise and combined exercise and diet interventions improved knee pain, disability, and performance scores at six months. Furthermore, the combined exercise and diet group demonstrated significantly greater maximum braking force and loading rates on biomechanical gait testing, indicating that the combination of exercise and diet may have further benefits on improved gait function when compared to exercise alone.
Taken together, a recent systematic review and meta-analysis showed that weight loss of over five percent, at a rate of 0.25 percent per week, could result in significant improvement in disability due to knee osteoarthritis over a 20-week period.
The Effects of Bariatric Weight Loss Surgery on Knee Osteoarthritis
While there have been no randomized control trials assessing the effects of weight loss surgery on knee osteoarthritis, multiple studies have shed light on the significant role that bariatric surgery can play.,,
Roux-en-Y gastric bypass. Several studies have assessed the effects of the Roux-en-Y Gastric Bypass (RYGB) on knee osteoarthritis symptoms. In a 2013 prospective follow-up study assessing the effects of bariatric surgery-induced weight loss on physical function and muscle structure, 16 patients who underwent RYGB showed statistically significant improvements in WOMAC stiffness and function scores, with an average increase of around 10 degrees in knee flexion range motion after 8.8 months.
A larger 2013 prospective follow-up study of 71 patients with obesity who underwent RYGB assessed the improvement in health-related quality of life factors including diabetes, hypertension, sleep apnea, and knee pain at 3, 6, and 12 months after surgery. At 12 months follow up, the number of patients with reportable knee pain decreased from 43 to 20, a statistically significant amount when analyzed by McNemar’s test.
Furthermore, a 2007 study assessed the effects of bariatric weight loss surgery on painful musculoskeletal conditions, including neck, shoulder, elbow, lower back, hip, and knee pain and function, in 48 subjects with obesity who underwent RYGB at an academic medical center. Of note, 47 of the subjects in this study were women. Of the 35 patients who initially reported knee pain, only 21 continued to report knee pain at 6 to 12 month follow up, statistically significant by paired t-test. Furthermore, not only did the number of individuals reporting knee pain decrease, but the intensity of the knee pain, the knee’s physical function, and knee stiffness all showed statistically significant improvement as assessed by the WOMAC index.
Laparoscopic Adjustable Gastric Banding. In addition to the effects of RYGB on knee osteoarthritis, multiple studies have investigated the effect of laparoscopic adjustable gastric banding (LAGB) on the symptoms of knee osteoarthritis as well. A 2007 study assessing the effect of LAGB on obesity-associated diseases, including diabetes, pulmonary disease, knee pain, and others in 145 patients with morbid obesity who underwent LAGB showed a decrease in the prevalence of knee pain from 47 percent to 38 percent over a 3 to 8 year follow-up period.
Not only has research demonstrated subjective improvements in knee pain and function from LAGB, but radiographic improvements have been shown as well. In a study of 64 patients undergoing LAGB with knee osteoarthritis, radiographic data showed an increase in medial joint space from 4.6mm to 5.25mm three months post-surgery. In addition, knee pain and function showed significant clinical improvement as measured by the American Knee Society Score index over the three-month period.
In a Chinese cohort assessing 10 patients who underwent LAGB to treat morbid obesity, knee pain resolved in the two patients that reported initial knee pain problems over a median follow-up period of 12 months.
Vertical Banded Gastroplasty. Although no longer commonly performed due to the advent of newer and more effective weight loss surgery procedures, in 1990, McGoey et al demonstrated a reduction in reported knee pain from 57 percent to 14 percent in a cohort of 105 consecutive patients undergoing vertical banded gastroplasty.
Mixed Groups. Studies examining the effect of weight loss surgery, without delineating surgery type, have also shown promise. In a study of 24 patients undergoing weight loss surgery, including RYGB, gastric banding, and sleeve gastrectomy, patients showed statistically significantly improved scores in knee pain, knee stiffness, and physical function in both activities of daily living and sports and recreation when assessed using the WOMAC index and the Knee Injury and Osteoarthritis Outcome Score at six months follow-up.
In a 2012 study following 25 patients that either underwent RYGB or LAGB three months post-surgery, the severity of knee pain decreased by 34 percent, walking speed increased by 15 percent, and step length increased by 4.8cm. These differences were all statistically significant when compared to a nonsurgical control group, demonstrating the potential benefits weight loss surgery could provide symptomatically as well as biomechanically.
The link between knee osteoarthritis and obesity has been well established in the medical literature. However, while the effects of both nonoperative and operative bariatric weight loss surgery have been shown to improve knee pain, function, and biomechanics, the quality of data in surgical management currently lags behind that of nonoperative options. While multiple randomized control trials demonstrate the benefits of diet and exercise on knee symptoms, surgical outcomes are currently limited to mostly prospective follow-up studies.8 In addition, no study to date has conducted a randomized control trial assigning patients with obesity with knee osteoarthritis to either nonoperative or operative weight loss management. As a result, direct comparisons between the benefits of nonoperative weight loss and surgical weight loss options on improvement in knee osteoarthritis symptoms cannot currently be made.
Future directions in the field would benefit from dedicated assessment into the effect of sleeve gastrectomy, a procedure growing in popularity, on knee osteoarthritis symptoms. The current available studies took place at times when LAGB and RYGB were more popular. Furthermore, it would be beneficial to define the relationship between body fat percentage lost after bariatric weight loss surgery and knee osteoarthritis. While this interesting association has been addressed in the nonoperative management literature, currently no weight loss surgery literature addresses the connection between body fat percentage lost through bariatric surgery and its effects on knee osteoarthritis. Improving these areas of research will be beneficial to future bariatric patients as they explore the possibilities of weight loss surgery.
Mr. Yang would like to thank Ayesha Abdeen, MD, FRCSC, for her assistance with reviewing this article. Dr. Abdeen is Instructor, Harvard Medical School; Director of Quality Assurance, Department of Orthopaedic Surgery; Chief, Division of Arthroplasty, Beth Israel Deaconess Medical Center, Boston, Massachusetts.
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FUNDING: No funding was provided.
FINANCIAL DISCLOSURES: The author reports no conflicts of interest relevant to the content of this article. address for correspondence: Brian W. Yang, E-mail: firstname.lastname@example.org