Advances in Skin & Wound Care:
Confounding Variables in Neuromusculoskeletal Function Associated with Self-inflicted Venous Ulcer Disease
Salcido, Richard MD, EdD
Richard “Sal” Salcido, MD, EdD, is the Editor-in-Chief of Advances in Skin & Wound Care and the Course Director for the Annual Clinical Symposium on Advances in Skin & Wound Care. He is the William Erdman Professor, Department of Physical Medicine and Rehabilitation; Senior Fellow, Institute on Aging; and Associate, Institute of Medicine and Bioengineering, at the University of Pennsylvania Health System, Philadelphia, Pennsylvania.
This month’s continuing education activity (page 82) allows us the opportunity to explore the influence a given condition has on a patient’s functional mobility, in this case venous ulcers. Dr Pieper, a content expert on venous ulcer disease, examines patients with intravenous drug abuse. This study examines the functional mobility of patients with self-injection–related venous ulcers (VU+) compared with the mobility of patients without venous ulcers (VU−). The investigators use 2 established mobility functional evaluation tools, the Five-Times-Sit-to-Stand1 and the Timed-Up-and-Go,2 to measure the influence that venous ulcers have on functional mobility. This particular study reveals several interesting questions related to intravenous drug–associated venous disease worth thinking about when reading this issue’s continuing medical education article.
Confounding variables or the “third variable”3,4 are also known as the mediator variable. It is aptly termed because the mediator variable may have a significant influence on the interpretation of the study. The term “confounding” is often described as “interference” by a third variable; this interference distorts the association being studied between 2 other variables4 because of a strong relationship with both of the other variables. In the case of this study, a confounding variable briefly alluded to in the study is the fact that a certain number of patients in the study may have had the manifestations of HIV–AIDS and pain.
HIV-AIDS: Variable in Mobility
The study discussed this diagnosis as having a negative effect on physical performance. Patients with HIV-AIDS may indeed initially present with myalgias, myopathies, neuropathies, pain, and limitations in functional mobility. Moreover, because the disease is now manageable with antiretroviral therapy, patients now have a reduction in opportunistic infections albeit with a shift in chronic diseases of the musculoskeletal system.5 This may negatively impact functional mobility, and the diseases are listed in descending order of prevalence: spinal axis disease, hip disease, knee, and other joints. These joints and muscles are important leverage points along the kinetic chain, which influence functional mobility.5
Arthritic variables include the presence of well-known diseases that impair mobility in the “baby boomer” population.6 They include degenerative joint disease, diabetes, and others. Chronic pain also has a “mediator effect” on physical function and mobility including self-efficacy. Coping or resiliency through self-efficacy or self-evaluation may be a powerful mediator that influences functional ability in and of itself.8
Because the human body has reserve and redundant functional capacity, it is difficult to ascribe a discrete venous ulcer to reduced locomotive function. In addition, we must consider that although we achieve statistical significance, it may not always correlate with clinical or functional significance. The authors appropriately conclude that rehabilitation interventions aimed at improving functional mobility and mitigation of falls and concomitant injury are the main goals.
Richard “Sal” Salcido, MD, EdD
1. Wallmann HW, Evans NS, Day C, Neelly KR . Interrater reliability of the Five-Times-Sit-to-Stand Test. Home Health Care Manage Pract. 2013; 25: 13–7.
2. Sousa N, Sampaio J . Effects of progressive strength training on the performance of the Functional Reach Test and the Timed Get-Up-and-Go Test in an elderly population from the rural north of Portugal. Am J Hum Biol. 2005; 17: 746–51.
3. 3. Mosby’s Medical Dictionary. 8th ed. Philadelphia, PA: Elsevier Inc; 2009; .
4. MacKinnon DP, Fairchild AJ . Current directions in mediation analysis. Curr Dir Psychol Sci. 2009; 18:(1): 16
5. Takhar SS, Hendey GW . Orthopedic illnesses in patients with HIV. Emerg Med Clin North Am. 2010; 28: 335–42.
6. Fowler-Brown A, Wee CC, Marcantonio E, Ngo L, Leveille S . The mediating effect of chronic pain on the relationship between obesity and physical function and disability in older adults. J Am Geriatr Soc. 2013; 61: 2079–86.
7. Judd DL, Thomas AC, Dayton MR, Stevens-Lapsley JE . Strength and functional deficits in individuals with hip osteoarthritis compared to healthy, older adults [published online ahead of print May 9, 2013]. Disabil Rehabil. 2013; .
8. Li F, Fisher KJ, Harmer P, McAuley E . Falls self-efficacy as a mediator of fear of falling in an exercise intervention for older adults. J Gerontol B Psychol Sci Soc Sci. 2005; 60:(1): P34–40.
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