Knee pain is present in about 50% of obese people, compared to in 12% of underweight people.6 It is anticipated that obese patients will have patellofemoral pain associated with the use of stairs and chairs; this relatively benign chronic weight-related pain can be managed by weight loss or decreasing patellofemoral activities. Medial and lateral compartment pain is associated with weight-bearing activities and is usually progressive.
Important historical elements are the magnitude of the existing disability and handicap of this chronic affliction that will inevitably worsen. The occurrence of minor trauma and acute exacerbating events causing knee pain are of less concern when a diagnosis of advanced osteoarthritis is made because the presenting event is only the beginning of a longer-term treatment program.
Imaging of obese patients with osteoarthritic symptoms should be limited to plain radiographs. A standing x-ray is the optimum imaging to delineate the magnitude of osteoarthritis, which is associated with a decrease in joint space on weight-bearing films. The role of MRI is negligible in the context of osteoarthritis and this imaging has no use in patients with morbid obesity. Millie’s MRI describes the hallmarks of osteoarthritis; these MRI findings are anticipated from the history and add little to the prognosis or management options.
A full blood count, biochemical profile and liver function tests are warranted investigations in an obese patient with osteoarthritis to provide a baseline. Malnutrition and endocrine abnormalities are the norm for morbidly obese patients.
Approach to management
Morbid obesity and osteoarthritis are both chronic conditions that inevitably erode the patient’s quality of life. It is highly desirable to have the patient work with a health practitioner in a co-operative fashion but many patients fail to appreciate the magnitude of their problems and are often reluctant to confront them. Many obese patients live within a sustained belief of denial and the rapid development of pain and loss of function may be the first time they are confronted with the implications of their being overweight. It is important to establish rapport as many patients will find discussions of their obesity embarrassing, and many have underlying psychological triggers that have initiated the event leading to their pathological weight gain.
The most efficacious treatment for the resolution of knee pain is substantial and sustained weight loss, a treatment that patients find hard to accept at initial consultations. The Framingham study concluded that a decrease in BMI of two points (equivalent to a 5-kg weight loss) led to a 50% reduction in the development of knee arthritis in women at 10 years.7 A useful ploy is to work with the patient in the context of preparing them for future surgical encounters for which the risks are excessive at this time.
Successful and sustained weight loss programs usually involve a multidisciplinary approach. Bariatric surgery has been shown to be a clinically effective and cost-effective intervention for patients with morbid obesity compared with nonsurgical intervention. Conversely, it is a sad disappointment that the common belief that patients will lose weight following knee replacement surgery is untrue, so it can be assumed that knee surgery has no benefit on weight-related medical conditions.
Medical treatment of osteoarthritis is a well-trodden path and the most effective interventions have been well studied. The effect size of placebo is 0.2, thus many patients have successfully encountered nontherapeutic drug and herbal treatments; most of these are futile but harmless. The routine medications of paracetamol and anti-inflammatories each have an effect size of 0.5 and are well recommended with consideration of an individual’s risk–benefit ratio. Opioids are inappropriate in young patients. Unloading painful joints with walking aids is usually successful, and the use of a single stick may unload the limb by 40% although the suggestion of this treatment is often poorly received.