Association of Thigh Muscle Strength With Knee Symptoms and Radiographic Disease Stage of Osteoarthritis: Data From the Osteoarthritis Initiative

Authors

  • Anja Ruhdorfer,

    Corresponding author
    1. Paracelsus Medical University, Salzburg, Austria
    • Institute of Anatomy, Paracelsus Medical University, Strubergasse 21, A5020 Salzburg, Austria. E-mail: anja.ruhdorfer@pmu.ac.at

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  • Wolfgang Wirth,

    1. Paracelsus Medical University, Salzburg, Austria
    2. Chondrometrics GmbH, Ainring, Germany
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    • Dr. Wirth has received consultant fees, speaking fees, and/or honoraria (less than $10,000 each) from Merck Sorono and Geneva, and owns stock and/or stock options in Chondrometrics GmbH.

  • Wolfgang Hitzl,

    1. Paracelsus Medical University, Salzburg, Austria
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  • Michael Nevitt,

    1. University of California, San Francisco
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  • Felix Eckstein,

    1. Paracelsus Medical University, Salzburg, Austria
    2. Chondrometrics GmbH, Ainring, Germany
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    • Dr. Eckstein has received consultant fees, speaking fees, and/or honoraria (less than $10,000 each) from Merck Sorono and AbbVie, and owns stock and/or stock options in Chondrometrics GmbH.

  • for the Osteoarthritis Initiative Investigators


Abstract

Objective

To determine whether thigh muscle strength differs between symptomatic and asymptomatic knees, and/or different radiographic strata of knee osteoarthritis (KOA).

Methods

Isometric extensor and flexor strength were analyzed in 3,809 Osteoarthritis Initiative participants (2,201 women and 1,608 men) with central radiographic Kellgren/Lawrence (K/L) grade readings. Isometric strength measurements were stratified by radiographic disease status (K/L grades 0, 1, 2, and 3/4) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain scores. Age-adjusted, separate-slopes analysis of covariance models was used to compare strength between “symptomatic” (WOMAC score range 5–20) and “asymptomatic” (WOMAC score = 0) legs within and across K/L grade strata. Exploratory analyses focused on strength normalized to body weight and symptom frequency.

Results

Isometric strength was significantly lower in symptomatic than in asymptomatic legs: −11 to −13% for extensor strength and −7 to −16% for flexor strength (P < 0.0001 for both) in men, and −9 to −17% (P = 0.029) for extensor strength, and −10 to −21% (P = 0.049) for flexor strength in women. Similar observations were made for pain frequency strata. Extensor and flexor strength were not significantly different across K/L grade strata in asymptomatic legs in either sex (P ≥ 0.12). However, strength normalized to body weight was lower at higher K/L grades in both sexes (P ≤ 0.02) because the body mass index was greater in participants with more advanced radiographic disease.

Conclusion

Knee symptoms (i.e., pain) appear to be the relevant determinant of isometric knee extensor and flexor strength in KOA, whereas no direct association between strength and radiographic severity was observed. These findings suggest that the reduction in thigh muscle strength in KOA is related to pain but not to the structural (radiographic) disease status.

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