Thigh Muscle Specific-Strength and the Risk of Incident Knee Osteoarthritis: The Influence of Sex and Greater Body Mass Index.
To determine whether lower thigh muscle specific-strength increases the risk of incident radiographic knee osteoarthritis (RKOA), and whether there exists a sex-specific relationship between thigh muscle specific-strength and body mass index (BMI).



A total of 161 Osteoarthritis Initiative participants (62% female) with incident RKOA (Kellgren/Lawrence grade 0/1 at baseline, developing an osteophyte and joint space narrowing grade ≥1 by year 4) were matched to 186 controls (58% female) without incident RKOA. Thigh muscle anatomical cross-sectional areas (ACSAs) were determined at baseline using axial magnetic resonance imaging scans. Isometric extensor and flexor muscle strength was measured at baseline, and specific strength (strength ÷ ACSA) was calculated. Logistic regression assessed the risk of incident RKOA associated with muscle specific-strength (with and without adjustment for BMI).



Lower knee extensor- and flexor-specific strength significantly increased the risk of incident RKOA in women but not in men (odds ratio 1.47 [95% confidence interval (95% CI) 1.10-1.96] and 1.41 [95% CI 1.06-1.89], respectively). The significant relationship in women was lost after adjustment for BMI. Lower specific strength was associated with higher BMI in women (r = -0.29, P < 0.001), but not in men, whereas absolute strength was associated with BMI in men (r = 0.28, P = 0.001), but not in women.



Lower thigh muscle specific-strength predicts incident RKOA in women, with this relationship being confounded by BMI. The sex-specific relationship between muscle specific-strength and BMI provides a possible explanation why women with muscle-strength deficits typically have a poorer prognosis than men with similar strength deficits.
Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria, and La Trobe University, Bundoora, Victoria, Australia.
Adam G
AG
Culvenor
Boston University School of Medicine, Boston, Massachusetts, and University of Manchester and Central Manchester NHS Foundation Trust, Manchester, UK.
David T
DT
Felson
Boston University School of Medicine, Boston, Massachusetts.
Jingbo
J
Niu
Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria.
Wolfgang
W
Wirth
Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria.
Martina
M
Sattler
Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria.
Torben
T
Dannhauer
Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria.
Felix
F
Eckstein
D000368:Aged; D015992:Body Mass Index; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000000981:diagnostic imaging* / Q000502:physiology*; D012307:Risk Factors; D012737:Sex Factors; D013848:Thigh / Q000000981:diagnostic imaging / Q000502:physiology