Treatment Considerations for Osteoarthritic Knee Pain in Patients with Obesity

| January 21, 2010

by James Choi, MD; Jonathan Schaffer, MD, MBA

Bariatric Times. 2010;7(1):12–14

Abstract
Knee pain is among the most common of health concerns in the population and bariatric patients have a well established positive association with knee osteoarthritis. Treatment for osteoarthritic knee pain is symptom based and relies heavily on the patient’s report of symptoms and functional limitations. Treatment modalities generally do not differ for patients with obesity as compared to their nonobese counterparts and range from nonoperative options, including physical therapy, orally administered analgesia, and knee injections, to operative intervention options with total knee arthroplasty as definitive treatment. Bariatric patients can present additional complexities for osteoarthritic knee pain treatment due to a noted risk for marginal ulceration with nonsteroidal anti-inflammatory drugs use in post-gastric bypass patients and an increased peri-operative risk with increasing body mass indices. Historically, orthopedic surgeons have been reluctant to embrace operative intervention due to the increased perioperative risk as well as concern for longevity and efficacy of the implant. Due to the increasing numbers of the bariatric population, it may be worthwhile to reconsider the current treatment pathways for osteoarthritic knee pain in bariatric patients. Future treatment considerations should include reevaluating criteria for determining successful treatment in bariatric patients while continuing to improve patient perioperative risk and chances for long-term improvement and symptom relief. Potential questions requiring further investigation include the following:

1.    For patients meeting criteria for both bariatric surgery and knee arthroplasty, which procedure should be performed first?
2.    How do we best minimize the exposure of patients to perioperative risk?
3.    Can we better understand the outcomes of post-bariatric procedure patients as compared to their general population and conservatively treated obese controls?
4.    What is the appropriate timing of procedures and should there be absolute body mass index cutoffs?
5.    What are the cost benefits and comparisons as well as quality of life considerations regarding bariatric and arthroplasty procedures?

Further study of outcomes of bariatric patients with osteoarthritic knee pain would be helpful to better delineate appropriate treatment protocols in the future.

Key words
obesity, bariatric surgery, knee pain, osteoarthritis treatment

Introduction
Knee pain is among the most common of health concerns in the population, and the subset of bariatric patients is no exception.[1,2] Independently, in the United States, obesity has prevalence in excess of 33 percent, and a 2006 Centers for Disease Control and Prevention (CDC) survey of adults reported an 18-percent incidence of knee pain within the past 30 days.[3,4] Bariatric patients have a well-established positive association with knee osteoarthritis, and it has been previously noted that body mass index (BMI) in young adulthood, a time when many patients are now choosing to pursue bariatric surgical options, may be a good predictor of subsequent osteoarthritis in later years.[5–7]

While the etiology of knee pain and treatment modalities can be wide ranging, this article will focus on existing medical knowledge of knee pain secondary to osteoarthritis in the bariatric population, considerations of the treatment options available for those afflicted with that diagnosis, and a discussion of the “best questions to address” in terms of future collaboration between and treatment options available to primary care physicians, orthopedic surgeons, and bariatric physicians and surgeons.

Anatomy
The knee is a modified hinge joint that experiences high contact and shear forces during ambulation. There are three alignments commonly observed in the knee: neutral, valgus (knock-knee), and varus (bow-legged).[8] Existing alignment of the knee can be exacerbated or altered by degenerative changes, which can significantly impact force distribution and wear patterns affecting the three compartments of the knee: medial, lateral, and patellofemoral. In level walking, the force experienced by the knee with each step is approximately four times the total weight of the body, and this increases to approximately eight times when ambulating down an incline.[9] In effect, the average bariatric patient’s knees will experience forces comparable to downhill walking at baseline and much higher forces with additional activity. The joint is stabilized by four primary ligaments—anterior cruciate ligament, posterior cruciate ligament, and medial and lateral collateral ligaments, as well as the surrounding musculature. Additionally, the knee is cushioned by synovial fluid and layers of cartilage and meniscus.

Injury or degeneration of any of these components can lead to knee pain. A history of prior injury and the effects of advancing age can lead to degeneration of the cartilage (osteoarthritis) with an unpredictable expression of pain and level of functional impairment. Previous studies have not correlated obesity with radiographic progression of osteoarthritis. Notably, it has been observed that obesity can increase the risk of osteoarthritis progression in those patients with neutral or valgus (knock-knee) alignment, but varus (bow-legged) aligned knees did not show the same risk progression.[10,11]

Evaluation and Therapy Options for Knee Pain
Osteoarthritic pain characteristically worsens with increased activity, particularly weight bearing, and improves with rest. Generally, patients report no systemic symptoms and on physical exam may have decreased range of motion, crepitus, mild joint effusion, and palpable osteophytic changes at the knee joint, though these findings may be more difficult to elucidate in patients with obesity.[12] Pain that continues and progresses warrants radiographic evaluation with joint space narrowing representing cartilage degeneration, characteristic of osteoarthritic changes. Unless there is suspicion of soft tissue injury, there is generally no need for further radiographic evaluation by computed tomography (CT) or magnetic resonance imaging (MRI) modalities.

Treatment for osteoarthritic knee pain is symptom based and relies heavily on the patient’s report of symptoms and functional limitations. There is not a predictive correlation between a patient’s complaint of symptoms to radiographic evaluation of osteoarthritis. The dependence on patient-reported symptoms for treatment action makes the understanding of pain reporting especially helpful. The results of the Swedish obese subjects study[13] indicate that patients with a higher BMI tend to have a higher prevalence of work-restricting pain (including the knees) than their general population counterparts. This same study also noted that postoperative female bariatric patients reported a greater level of improvement in their symptoms as compared to their nonoperative peers and that work-restricting knee, hip, and ankle pain was more responsive than axial musculoskeletal complaints.[13]

At present, treatment of osteoarthritic knee pain is based upon relief of symptoms beginning with nonoperative options, and treatment modalities generally do not differ for patients with obesity as compared to their nonobese counterparts. Pharmacologic therapy is primarily targeted at analgesia, and periodic use of analgesics can be effective for intermittent and mild-to-moderate symptoms. Nonsteroidal anti-inflammatory drugs (NSAIDS) are often effective for osteoarthritis pain.[14] The use of NSAIDS is complicated in the gastric bypass patient population due to an increased risk of adverse gastrointestinal side effects, which include development of marginal ulcers at the previously created anastomosis sites. NSAIDs should be used with caution and possibly with proton pump inhibitor therapy.[15] In the gastric bypass population, there has been little definitive guidance on the most effective pharmacologic alternatives given the risks of NSAID use in this patient subset. Narcotics are generally considered a pharmacologic last option for advanced osteoarthritis pain that is refractory to other treatments, and systemic corticosteroids have not been shown to be effective for pain relief although localized injections that are discussed later can be effective for relief of symptoms.[14] Physical therapy targeted at the surrounding musculature, specifically quadriceps strengthening, can be effective in providing pain relief.[16]

Among more invasive interventions, knee injections fall under two categories: corticosteroid and viscosupplementation. Corticosteroid injections reduce the inflammatory response within the knee joint and can provide good relief of variable duration of weeks to months, but rarely are more than two or three intra-articular injections to the same joint administered per year for concern of potentially progressive cartilage damage.[14] Additionally, recent studies have demonstrated that bupivacaine, a commonly used intra-articular local anesthetic often combined with a corticosteroid, has a significantly increased in-vitro toxicity to human articular chondrocytes when compared to ropivacaine, and further research on long-term effects should be followed closely.[17] Viscosupplementation of hyaluronates is intended to counteract the reduction of concentration and size of hyaluronan, a key component of synovial fluid, which occurs in osteoarthritis. Clinical trials of viscosupplementation have yielded highly variable results ranging from no effect to improvement in symptoms lasting up to one year.

Physicians should also be aware of patient-directed therapies as well. In the context of osteoarthritis, this primarily consists of the nutritional supplements glucosamine and chondroitin, and National Institute of Health-sponsored research studies to date have not shown significant efficacy in symptom relief.[14,18]

The end-stage therapy for osteoarthritic knee pain is surgical intervention, including arthroscopy, osteotomy, partial knee arthroplasty, and total knee arthroplasty.19 Should this be required, total knee arthroplasty is the definitive treatment. Other operative modalities that can potentially be offered include a partial knee arthroplasty, including patello-femoral arthroplasty for patients with specifically isolated compartment osteoarthritis. Knee arthroplasty is generally regarded as a highly successful procedure with predictably good outcomes. Historically, orthopedic surgery has been somewhat reticent to embrace operative treatment for patients with high BMIs. This is perhaps no better exemplified than by the decision of the East Suffolk (UK) health board to prioritize lower extremity arthroplasty for those patients that are not overweight or obese. The two most cited reasons for not proceeding with arthroplasty in the obese patient set are a high rate of perioperative complications (e.g., wound healing and infections) and concern for the longevity and efficacy of the implant. Winiarsky et al[20] showed a significantly increased postoperative infection rate (26% vs. 2%) for patients with morbid obesity undergoing a total knee arthroplasty. A review article by Gillespie and Porteous21 showed a trend of increasing complication rates with increasing BMI though no definitive cutoff could be determined. A study by Amin et al[23] in 2006 showed that arthroplasty patients with BMIs greater than 40kg/m2 had clinical outcome scores significantly lower than the control group and a higher rate of revision and perioperative complications. Amin et al recommended that patients lose weight and maintain that weight loss prior to arthroplasty and should be counseled about the potential for inferior results without weight loss.[22] In 2000, Parvizi et al[24] reported seeing excellent hip and knee arthroplasty results in patients who were postoperative from bariatric procedures with a mean BMI change from 49kg/m2 to 29kg/m2.

Discussion/Conclusions
Although the connection between these two morbidities is strong, the course of treatment is not well defined. From the orthopedist’s perspective, a high BMI may be viewed as potentially exclusionary from surgical treatment of osteoarthritis, at least until the patient achieves some degree of stable and sustained weight loss. Looking from the bariatric surgeon’s perspective, bariatric procedures have not historically promoted any efficacy in improving musculoskeletal concerns to the extent that has been the case for improving cardiovascular and endocrine morbidities. In the literature today, there is a paucity of publications addressing the long-term outcomes of joint arthroplasty in the context of osteopenia that is generated by the malabsorptive state created by a gastric bypass procedure. This leads us to a number of questions as to the appropriate path of care for the patient with obesity and progressive knee osteoarthritis.

1.    For patients meeting criteria for both bariatric surgery and knee arthroplasty, which procedure should be performed first?
2.    How do we best minimize the exposure of patients to perioperative risk?
3.    Can we better understand the outcomes of post-bariatric procedure patients as compared to their general population and conservatively treated obese controls?
4.    What is the appropriate timing of procedures? Should there be absolute BMI cutoffs?
5.    What are the cost benefits and comparisons as well as quality of life considerations regarding bariatric and arthroplasty procedures?

Some points for future consideration include the following: 1) understanding noncongruence in age of the typical bariatric versus arthroplasty patient; 2) determining whether or not primary care physicians and orthopedists who have patients with BMIs of greater than 35 presenting to their clinic with knee pain should consider referring those patients for evaluation by a bariatric clinic; and 3) determining when a “suboptimal” arthroplasty procedure is in the best interest of the patient. Bariatric patients tend to present at a younger age than the typical arthroplasty candidate. The youngest bariatric patients would generally not be considered for arthroplasty; however, patients progressing into their 40s to 50s may be a potential subset for future outcomes studies. If weight loss through invasive restrictive procedures or nonoperative methods can improve symptoms and delay the need for a primary orthopedic procedure, it may be worthwhile to further investigate outcomes of each population group as well as gain a better understanding of the pain response and symptom reporting as compared to current weight for bariatric patients. It may also be worthwhile to consider the appropriateness of arthroplasty in specific high BMI patients. Amin et al[23] demonstrated a significant difference in Knee Society Scores between patients with obesity and control patients; however, an additional consideration may be that the arthroplasty patient with obesity may not need to generate the same quantitative score to experience an improvement in function and decrease in pain. Is it acceptable to expect less than standard results from the surgeon’s perspective as long as the patient is aware of the increased risks and diminished benefits when compared to patients with lower BMIs?

There is evidence that correlation exists between obesity and progression of knee pain.[5–7] In the patient population with BMI in excess of 40, research indicates that these patients tend to have suboptimal postoperative arthroplasty results and a higher incidence of perioperative complications than their knee pain control peers. A gray area exists for patients with BMIs between 30 and 40 with a noted increasing trend to suboptimal results and higher complication rates but no definitive cutoff mark. In limited studies, patients who require knee arthroplasty after bariatric surgery have done well, and long-term follow up of those patients will yield useful information. Presently, it may be worthwhile to consider a referral to a bariatric surgeon by a primary care physician or orthopedic surgeon for patients with obesity presenting with knee pain. After undergoing bariatric surgery, these patients may see improvement in the common comorbidities of high BMI patients as well as improvement in their osteoarthritic knee pain symptoms. This also generates the potential for delaying the need for any orthopedic surgical intervention and reducing the likelihood of perioperative complications and need for revision surgery should there be a need for arthroplasty in the future. Further study of outcomes of bariatric patients with osteoarthritic knee pain would be helpful to further delineate appropriate treatment protocols in the future.

References
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Funding:
The authors have no financial disclosures relevant to the content of this article.

Author affiliation:
Dr. Choi, is from the Department of Orthopaedic Surgery, Massachusetts General Hospital, Boston, Massachusetts. Dr. Schaffer is from the Orthopaedic and Rheumatologic Institute, Cleveland Clinc, Cleveland, Ohio.

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