Original Research A Preliminary Assessment of a Novel Pneumatic Unloading Knee Brace on the Gait Mechanics of Patients With Knee Osteoarthritis Ugo Della Croce, PhD, Fausto Crapanzano, MD, Ling Li, MSPH, Patrick K. Kasi, MS, Benjamin L. Patritti, PhD, Chiara Mancinelli, MS, David J. Hunter, MD, PhD, Dimitrije Stamenovi  c, PhD, William F. Harvey, MD, MSc, FACR, Paolo Bonato, PhD Objectives: To determine whether a knee brace incorporating inflatable air bladders can alter the net peak external knee adduction moment in persons with medial compartment knee osteoarthritis. Design: Prospective cohort study. Setting: Motion analysis laboratory. Participants: Subjects (n ¼ 18) diagnosed with knee osteoarthritis as defined by the Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Methods: Instrumented gait analysis was performed while subjects walked with and without the knee brace. When subjects wore the knee brace, the air bladders were either uninflated or inflated to 7 psi. The net external knee adduction moment was obtained by subtracting the abduction moment produced by the knee brace (estimated using a finite element analysis model) from the external knee adduction moment (estimated using a camera-based motion analysis system). Main Outcome Measurements: The net external knee adduction moment was compared across all testing conditions. Results: A 7.6% decrease in net peak external knee adduction moment was observed when subjects wore the knee brace uninflated compared with when they did not wear the brace. Inflation of the bladders to 7 psi led to a 26.0% decrease in net peak external knee adduction moment. Conclusions: The results of the study suggest that the effects of an unloading knee brace may be enhanced by incorporating inflatable air bladders into the design of the brace, thus leading to an improved correction of the excessive peak external knee adduction moment observed in patients with medial compartment knee osteoarthritis. PM R 2013;-:1-9 INTRODUCTION Malalignment of the lower limb during gait is a well-known mechanical risk factor for knee osteoarthritis (OA) [1]. The external adduction moment at the knee during the stance phase of gait has also been associated with the progression of knee OA [2]. Load distri- bution at the knee is affected by deviations in the alignment of the hip, knee, and ankle— the so-called “loading axis” [3,4]. In a varus deformed knee, this axis passes medially to the knee joint, resulting in an excessive external adduction moment at the knee, which forces the knee toward an increased varus attitude and an increased loading of the medial compartment of the knee [5,6]. The latter has been shown to increase OA progression of the medial knee compartment [5]. In persons with medial knee OA, the peak external knee adduction moment is approx- imately 25% greater (ie, approximately 1% of bodyweight  height [7,8]) than normal values of the peak external knee adduction moment that causes loading of the medial compartment of the knee during gait [8,9]. Previous studies suggest that excessive peak external knee adduction moment values and malalignment of the lower extremity are linked to pain and U.D.C. Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston MA; POLCOMING Department, Information Engineering Unit, University of Sassari, Sassari, Italy Disclosure: nothing to disclose F.C. Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston MA; Physical Rehabilitation Medicine, "San Giovanni di Dio" Hospital, Agrigento, Italy Disclosure: nothing to disclose L.L. Division of Rheumatology, Tufts Medical Center, Boston MA Disclosure: nothing to disclose P.K.K. Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston MA Disclosure: nothing to disclose B.L.P. Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston MA; Department of Rehabilitation and Aged Care, Repatriation General Hospital, Daw Park, Adelaide, South Australia Disclosure: nothing to disclose C.M. Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston MA Disclosure: nothing to disclose D.J.H. Rheumatology Department, Royal North Shore Hospital and Kolling Institute, University of Sydney, Sydney, NSW, Australia Disclosure: nothing to disclose D.S. Department of Biomedical Engineering, Boston University, Boston, MA Disclosure: nothing to disclose W.F.H. Division of Rheumatology, Tufts Med- ical Center, Boston MA Disclosure: nothing to disclose P.B. Physical Medicine and Rehabilitation, Harvard Medical School, 300 First Avenue, Charlestown, MA 02129. Address correspon- dence to: P.B.; e-mail: pbonato@partners.org Disclosure: nothing to disclose Peer reviewers and all others who control content have no relevant financial relation- ships to disclose. Submitted for publication June 2, 2012; accepted June 18, 2013. PM&R 1934-1482/13/$36.00 Printed in U.S.A. ª 2013 by the American Academy of Physical Medicine and Rehabilitation Vol. -, 1-9, - 2013 http://dx.doi.org/10.1016/j.pmrj.2013.06.008 1