Osteoarthritis Supplement Osteoarthritis in the Disabled Population: A Mechanical Perspective David C. Morgenroth, MD, Alfred C. Gellhorn, MD, Pradeep Suri, MD, MS Abstract: Primary disabling conditions, such as amputation, not only limit mobility, but also predispose individuals to secondary musculoskeletal impairments, such as osteoarthri- tis (OA) of the intact limb joints, that can result in additive disability. Altered gait biomechanics that cause increased loading of the intact limb have been suggested as a cause of the increased prevalence of intact limb knee and hip osteoarthritis in this population. Optimizing socket fit and prosthetic alignment, as well as developing and prescribing prosthetic feet with improved push-off characteristics, can lead to reduced asymmetric loading of the intact limb and therefore are potential strategies to prevent and treat osteoarthritis in the amputee population. Research on disabled populations associated with altered biomechanics offers an opportunity to focus on the mechanical risk factors associ- ated with this condition. Continued research into the causes of secondary disability and the development of preventive strategies are critical to enable optimal rehabilitation practices to maximize function and quality of life in patients with disabilities. PM R 2012;4:S20-S27 INTRODUCTION Osteoarthritis (OA) is a chronic degenerative disorder, characterized by articular cartilage degradation and periarticular bone remodeling. OA causes joint pain and stiffness, and commonly causes functional impairment and reduced independence in older adults [1]. Knee OA is the most common cause of mobility-related disability in the elderly population [2]. OA can be even more functionally devastating to individuals with preexisting disabili- ties. For instance, many individuals with a lower extremity amputation face mobility challenges at baseline secondary to walking with a prosthetic limb. The development of symptomatic OA in the joints of the intact limb can have an additive debilitating effect on mobility and quality of life in this population. The etiology of OA is thought to be multifactorial: a combination of potentially modifi- able factors related to abnormal joint mechanics, superimposed on underlying risk factors including age, gender, race/ethnicity, and other specific genetic factors [3-5]. Factors that cause abnormal joint mechanics thought to be associated with the development and progression of OA include obesity, prior joint trauma, joint deformity and malalignment, abnormal gait mechanics, and certain occupations and sport activities [4,6-12]. Primary disabilities, such as amputation or spinal cord injury, often affect gait or upper extremity mechanics, which cause increased or altered repetitive loading of joints. These mechanical joint loading abnormalities are potentially causative of the higher incidence of OA reported in some disabled populations relative to the general population [13-18]. Research on specific populations with altered biomechanics offers an opportunity to focus on the mechanical risk factors that can otherwise be challenging to distinguish from underlying systemic risk factors in the general population. The purpose of this article is to review, critique, and organize the pertinent literature in an effort to shed light on the biomechanical factors related to the development, prevention, and treatment of OA in the disabled population. This article will focus on knee and hip OA in the lower extremity amputee population, because the vast majority of existing literature on OA in disabled populations relates to this area. D.C.M. RR&D Research Center, Veterans Af- fairs Puget Sound Healthcare System, Seattle, WA; Department of Rehabilitation Medicine, University of Washington, Seattle, WA. Ad- dress correspondence to: D.C.M., VAPSHCS, RCS-117, 1660 S. Columbian Way, Seattle, WA 98108; e-mail: dmorgen@uw.edu Disclosure: 8, VA Career Development Award A.C.G. Department of Rehabilitation Medi- cine, University of Washington, Seattle, WA Disclosure: nothing to disclose P.S. Division of Physical Medicine and Reha- bilitation, Veterans Affairs Boston Healthcare System, Boston, MA; Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, MA; Spaulding Rehabilitation Hospital, Boston, MA; New England Baptist Hospital, Boston, MA Disclosure: 8B, NIH (grant #K12 HD001097) Disclosure Key can be found on the Table of Contents and at www.pmrjournal.org PM&R © 2012 by the American Academy of Physical Medicine and Rehabilitation 1934-1482/12/$36.00 Vol. 4, S20-S27, May 2012 Printed in U.S.A. DOI: 10.1016/j.pmrj.2012.01.003 S20