Hip Muscle Weakness in Individuals With Medial Knee Osteoarthritis RANA S. HINMAN, MICHAEL A. HUNT, MARK W. CREABY, TIM V. WRIGLEY, FIONA J. MCMANUS, AND KIM L. BENNELL Objective. To compare the strength of the hip musculature in people with symptomatic medial knee osteoarthritis (OA) with asymptomatic controls. Methods. Eighty-nine people with knee OA and 23 controls age >50 years were recruited from the community. The maximal isometric strength (torque relative to body mass) of the hip abductors, adductors, flexors, extensors, and internal and external rotators was evaluated using hand-held dynamometry or a customized force transducer apparatus. Uni- variate linear models with age and sex included as covariates were used to compare muscle strength between groups. Results. In people with knee OA, significant strength deficits were evident for all hip muscle groups evaluated (P < 0.05). Compared with controls, strength deficits ranged from 16% (hip extensors) to 27% (hip external rotators) after accounting for differences in sex and age between groups. Conclusion. People with knee OA demonstrate significant weakness of the hip musculature compared with asymptom- atic controls. It is not clear if hip muscle weakness precedes the onset of knee OA or occurs as a consequence of disease. Findings from this study support the inclusion of hip strengthening exercises in rehabilitation programs. Introduction Knee osteoarthritis (OA) is a chronic problem affecting a significant proportion of older people (1) and is a major cause of pain and disability. Muscle weakness, particu- larly of the quadriceps, is one of the earliest clinical signs of knee OA and has long been recognized as a hallmark of the disease. In fact, muscle weakness may precede disease onset and play a role in knee OA pathogenesis (2). Since muscle strengthening improves pain and function in knee OA (3), strengthening exercise is widely recommended for the condition (4). However, most research has focused on the role of quadriceps strength in knee OA, with little attention given to other lower extremity musculature. A thorough understanding of the impact of knee OA on other muscle groups is required if optimal strengthening pro- grams are to be developed and employed. Increasing research suggests that hip muscle weakness may be associated with knee OA, but little research has evaluated this to date. The medial tibiofemoral compartment is the most com- mon site of disease at the knee, presumably due to greater loads borne across this compartment relative to the lateral compartment, and research evaluating risk factors for me- dial knee OA progression has highlighted the potential importance of hip muscle strength. Chang et al (5) demon- strated that a greater internal hip abduction moment dur- ing gait protected against ipsilateral medial OA progres- sion over a period of 18 months. Chang and colleagues postulated that hip abductor weakness may result in ad- ditional contralateral pelvic drop, shifting the center of mass toward the swing extremity, which therefore in- creases forces across the medial compartment of the stance extremity and hastens disease progression. Although plau- sible, little research has directly evaluated whether people with medial knee OA do, in fact, demonstrate weakness of the hip abductors, or any other hip muscle group, com- pared with asymptomatic controls. This study aimed to compare strength of the hip abduc- tor, adductor, internal rotator, external rotator, flexor and extensor muscles in people with symptomatic medial knee OA and an asymptomatic control group. It was hypothe- sized that participants with knee OA would be signifi- cantly weaker in all hip muscle groups compared with controls. Supported by the National Health and Medical Research Council (grant 454686). Dr. Hunt’s work was supported by a Sir Randal Heymanson Fellowship from the University of Melbourne. Rana S. Hinman, BPhysio, PhD, Michael A. Hunt, BHK, MSc, MPT, PhD, Mark W. Creaby, PhD, BSc(Hons), Tim V. Wrigley, MSc, Fiona J. McManus, BPhysio(Hons), Kim L. Bennell, BAppSci, PhD: Melbourne Physiotherapy School, University of Melbourne, Melbourne, Australia. Address correspondence to Rana S. Hinman, BPhysio, PhD, Center for Health Exercise and Sports Medicine, School of Physiotherapy, The University of Melbourne, Parkville, Victoria, Australia 3010. E-mail: ranash@unimelb. edu.au. Submitted for publication October 22, 2009; accepted in revised form March 11, 2010. Arthritis Care & Research Vol. 62, No. 8, August 2010, pp 1190 –1193 DOI 10.1002/acr.20199 © 2010, American College of Rheumatology CONTRIBUTIONS FROM THE FIELD 1190