Sarcopenia’s Role in Knee OA Progression
OrthoBuzz occasionally receives posts from guest bloggers. This guest post comes from Jeffrey Stambough, MD, in response to a recent study in Arthritis & Rheumatology.
The incidence of total knee arthroplasty to treat end-stage knee osteoarthritis (OA) continues to rise even in the face of patient risk-stratification tools and alternative payment models. Consequently, payers, patients, and their doctors are placing a premium on methods to prolong the native knee joint and delay or avoid surgery. This partly explains the explosion of interest in biologics and the subsequent checkreins being put in place regarding their use.
As the AAOS clinical practice guidelines for the management of knee arthritis clearly state, the best management for symptoms of knee arthritis remains weight loss and self-directed physical activity. However, there is uncertainty regarding which subtypes of patients are likely to achieve OA symptom benefits with different weight-loss strategies.
A recent large, multicenter cohort study published in Arthritis & Rheumatology attempted to further characterize patient body composition and its association with knee OA. Using whole-body dual x-ray absorptiometry (DXA) measures of fat and muscle mass, researchers classified patients into one of four categories: nonobese nonsarcopenic, sarcopenenic nonobese, nonsarcopenic obese, or sarcopenic obese. Sarcopenia is the general loss of muscle mass associated with aging. If orthopaedic surgeons better understand how fat and muscle metabolism change with time and affect inflammation and chronic disease, they may be able to provide patients with additional insight into preventive measures.
Using DXA-derived calculations, the authors observed that among older adults, the relative risk of developing clinically significant knee osteoarthritis (Kellgren-Lawrence grade ≥2) at 5 years was about 2 times greater in both sarcopenic and nonsarcopenic obese male and female patients compared to nonobese, nonsarcopenic patients. Sarcopenia alone was not associated with risk of knee OA in women or men. In a sensitivity analysis focusing on BMI, men showed a 3-fold greater risk of knee OA if they were sarcopenic and obese, relative to nonobese nonsarcopenic patients.
The takeaway from this study is that focusing solely on fat/weight loss may overlook a valuable opportunity to slow the progression of knee arthritis in some patients. Further studies are needed to validate the contribution of low muscle mass to the development and progression of symptomatic knee arthritis.
Read this related OrthoBuzz post about sarcopenia’s relationship to mortality in elderly patients with acetabular fractures.
Jeffrey B. Stambough, MD is an orthopaedic hip and knee surgeon, an assistant professor of orthopaedic surgery at University of Arkansas for Medical Sciences, and a member of the JBJS Social Media Advisory Board.
Sarcopenia: An Independent Predictor of Mortality in Geriatric Acetabular Fractures
OrthoBuzz occasionally receives posts from guest bloggers. This guest post comes from Matthew Herring, MD, in response to a recent study in the Journal of Orthopaedic Trauma.
Fractures in the elderly are a growing problem in developed countries and generally carry a significant morbidity and mortality burden. When considering treatment strategies and making prognoses in this patient population, our ability to stratify patient frailty may be just as or more important than classifying the fracture. In a recent study in the Journal of Orthopaedic Trauma, Mitchell et al. evaluate the role of sarcopenia, an age-related loss of muscle mass, in predicting 1-year mortality among elderly patients with acetabular fractures.1
The authors performed a retrospective review of nearly 150 patients >60 years of age who sustained an acetabular fracture between 2003 and 2014. The authors used the lowest quartile of the psoas:lumbar vertebral index (PLVI) in the cohort as a surrogate for sarcopenia. The PLVI is calculated by measuring the cross-sectional area of the psoas muscle bellies at the L4 level and dividing that number by the cross-sectional area of the L4 vertebral body measured at the superior endplate (see image). Lower PLVIs represent greater loss of muscle mass.
After controlling for confounding variables, the authors found that sarcopenia was an independent risk factor for 1-year mortality. Specifically, patients with sarcopenia had a 32.4% 1-year mortality rate compared to a rate of 11.0% in patients without sarcopenia. Age and injury severity score (ISS) were also predictive of 1-year mortality, and patients with all 3 factors (age >75 years, ISS >14, and sarcopenia) had a mortality rate of 90%.
This article highlights the importance of risk-stratifying patients in ways that account for more than their presenting injuries. In the elderly population, chronologic age is only one of many indicators of frailty. Sarcopenia may be another marker that we can use to better understand the general well-being of our patients. As Mitchell et al. mention, more research must be done to precisely define a PLVI cutoff for sarcopenia to make this index a clinically useful tool. Ultimately, doing so will allow us to offer elderly patients and their families more thoughtful and evidence-based counseling regarding treatment and prognosis.
Matthew Herring, MD is a senior orthopaedic resident at the University of Minnesota and a member of the JBJS Social Media Advisory Board.
Reference
- Mitchell, Phillip M., et al., Sarcopenia is Predictive of 1-year Mortality After Acetabular Fractures in Elderly Patients.” Journal of Orthopaedic Trauma, June 2018; 32 (6) : 278-282.
JBJS Editor’s Choice: Sarcopenia + Acetabular Fracture = Increased Mortality
In the February 1, 2017 edition of The Journal, Deren et al. provide an important analysis of muscle mass as it relates to mortality in older patients with an acetabular fracture. Among 99 fracture patients studied retrospectively, 42% had sarcopenia, defined in this study as a skeletal muscle index at the L3 vertebral body of <55.4 cm2/m2 for men and <38.5 cm2/m2 for women.
Deren et al. found that low BMI was associated with sarcopenia and that patients with sarcopenia were significantly more likely than patients without sarcopenia to sustain their skeletal injury from a low-energy mechanism. Sarcopenia was also associated with a higher risk of 1-year mortality, especially when in-hospital deaths were excluded. While the authors note that there’s no consensus definition for clinically diagnosing sarcopenia, they conclude that “sarcopenia based on the skeletal muscle index may be a better predictor of mortality than other commonly used classification
systems.”
There are important subtextual messages in this study for all physicians who manage geriatric patients. Maintenance of muscle mass by resistance exercise (lifting weights, isometrics, etc.) is of critical importance in limiting fall risk and maintaining good balance and bone density. Dietary considerations are intertwined with exercise in maintaining muscle mass among older patients. Resistance training and cardio exercise help to maintain appetite, and adequate protein intake is of utmost importance. When families and medical teams work together, the risk of sarcopenia can be minimized, resulting in lower rates of falls, fewer low-energy fractures, and less mortality.
Marc Swiontkowski, MD
JBJS Editor-in-Chief
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