Association Among Neuromuscular and Anatomic Measures for Patients With Knee Osteoarthritis Trevor B. Birmingham, PhD, John F. Kramer, PhD, Alexandra Kirkley, MD, J. Timothy Inglis, PhD, Sandi J. Spaulding, PhD, Anthony A. Vandervoort, PhD ABSTRACT. Birmingham TB, Kramer JF, Kirkley A, Inglis JT, Spaulding SJ, Vandervoot AA. Association among neuromuscular and anatomic measures for patients with knee osteoarthritis. Arch Phys Med Rehabil 2001;82:1115-8. Objective: To investigate neuromuscular and anatomic fac- tors involved in varus gonarthrosis by identifying measures associated with degenerative changes. Design: Descriptive study. Individual measures that ex- plained substantial portions of the variability in ratings of knee joint– degenerative changes in patients with knee medial com- partment osteoarthritis. Setting: Outpatient orthopedic clinic and biomechanics and muscular assessment laboratory. Patients: Volunteer sample of 20 subjects (age range, 59  9yr) with no history of neurologic disease. Interventions: Not applicable. Main Outcome Measures: We assessed degenerative changes, varus alignment, standing balance, and knee proprio- ception. Weight-bearing radiographs were used to assess the extent of degenerative changes and the degree of varus align- ment. Single-limb standing balance control was assessed through tests performed on a force platform. Knee propriocep- tion was assessed with an isokinetic dynamometer, using a joint angle replication test. Results: Forward-stepwise multiple linear regression indi- cated that the extent of degenerative changes could be best predicted from a linear combination of the independent vari- ables, varus alignment, and standing balance (R = .80, F 2,17 = 14.81, p = .0002). Sixty-four percent of the variability in ratings of degenerative changes was explained by alignment and standing balance measures (37% by varus alignment, 27% by standing balance). Alignment and balance measures were poorly correlated (r = .12, p = .63), further suggesting that they provided different information about gonarthrosis. Conclusions: Although varus alignment is widely accepted as a clinically important factor in gonarthrosis, and is the focus of many treatment efforts, our results suggest that objective measures of standing balance are also important. As a result, the potential impact of rehabilitation to improve the control of standing balance should be further evaluated in this patient population. Key Words: Balance; Knee joint; Osteoarthritis, knee; Re- habilitation. © 2001 by the American Congress of Rehabilitation Medi- cine and the American Academy of Physical Medicine and Rehabilitation A NATOMIC AND NEUROMUSCULAR measures have been identified as factors that may initiate or accelerate knee joint degenerative changes. A well-known example of the importance of anatomic characteristics is the development of medial gonarthrosis in excessive varus alignment. 1,2 Although less clearly understood, deficits in neuromuscular processes, such as postural control and knee proprioception, have also been proposed as potentially important and often overlooked components of osteoarthritis. 3-6 Based on various assessment techniques, gonoarthrosis com- promises the control of standing balance and knee propriocep- tion. 7-13 Although deficits in those specific aspects of neuro- muscular performance may be apparent when patients are compared with control groups that have healthy knees, 2,7,9,14-17 the clinical importance of those findings is unclear because the extent to which those measures are related to other disease characteristics is unknown. Determining the association among the extent of knee joint degenerative changes, varus alignment, standing balance, and proprioception would help establish the relative importance of these measures, as well as their potential as assessment tools and outcome measures. Our objective in this study was to gain a better understanding of the neuromuscular and anatomic factors involved in varus gonarthrosis by identifying measures associated with degener- ative changes. While causation cannot be inferred from the study design, the construct evaluated was that measures that explain substantial portions of the variability in ratings of degenerative changes can be considered important for this patient population. METHODS Subjects Twenty patients (table 1) diagnosed with varus gonarthrosis by an orthopedic surgeon at the University of Western Ontario Fowler Kennedy Clinic were studied. All had varus alignment of greater than 0°, complained of pain localized primarily to the medial compartment, and met the criteria suggested by Altman et al 14 for the diagnosis of osteoarthritis. These criteria included knee pain, age of more than 18 years, osteophytes seen on radiographs, and at least 1 of the following: age more than 50 years, morning stiffness lasting longer than 30 minutes, or crepitus with active knee motion. Subjects were excluded if they had a neurologic disorder, surgery on either knee in the last 6 months, or symptomatic disease of the hip, ankle, or foot. Subjects were recruited from a consecutive sample of patients with varus gonarthrosis presenting at the outpatient orthopedic clinic, or were selected from individuals answering an adver- tisement in the local newspaper. From the Faculties of Health Sciences (Birmingham, Kramer, Kirkley, Spaulding, Vandervoort) and Medicine (Kirkley), University of Western Ontario, London, Ont; and School of Human Kinetics, University of British Columbia (Inglis), Vancouver, BC, Canada. Accepted in revised form September 20, 2000. Supported in part by the Medical Research Council and Physiotherapy Foundation of Canada. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Trevor B. Birmingham, PhD, Elborn College, Schl of Physical Therapy, Faculty of Health Sciences, University of Western Ontario, London, Ont N6G 1H1, Canada, e-mail: tbirming@julian.uwo.ca. 0003-9993/01/8208-6324$35.00/0 doi:10.1053/apmr.2001.24306 1115 Arch Phys Med Rehabil Vol 82, August 2001