Specific muscle strength is reduced in female knees with incidcence radiographic osteoarthritis

Abstract

s / Osteoarthritis and Cartilage 21 (2013) S63–S312 S220 415 SPECIFIC MUSCLE STRENGTH IS REDUCED IN FEMALE KNEES WITH INCIDCENCE RADIOGRAPHIC OSTEOARTHRITIS M. Sattler y, J. Niu z, T. Dannhauer y, W. Wirth y, D. Felson z, F. Eckstein y. y Paracelsus Med. Univ., Salzburg, Austria; zClin. Epidemiology Res. & Training Unit, Boston Univ. Sch. of Med., Boston, MA, USA Purpose: Quadriceps strength plays an important role in knee biomechanics. Quadriceps weakness has been shown to be related to the onset of knee symptoms in women, but has not been associated with incident radiographic knee OA (KOA). However, previous studies have not examined muscle specific strength, a potentially more physiologically relevant measure of strength that accounts for the individual cross sectional area (CSA) of muscles. Here we explore whether specific strength differs between knees with incident radiographic KOA vs. nonincident controls. Methods: Of 4796 Osteoarthritis Initiative participants, we studied knees that showed incident radiographic KOA (central readings, fixed flexion radiographs). These were defined as Kellgren and Lawrence grade (KLG) 0 or 1 knees at baseline, in which the combination of a definite osteophyte AND joint space loss (OARSI JSN>grade1) developed by 48 month follow up. These knees were matched by baseline KLG0/KLG1 frequency (w30%/70%) to control knees without incident KOA at 48M. Of 447 case and control knees, 342 had axial T1weighted spinecho MRIs of the thigh AND maximal isometric strength measures of the extensors and flexors (Good Strength Chair, Metitur). To determine CSAs of the quads, hamstrings and adductors, we selected an MRI slice located at 30% femoral length (distal to proximal) based on an estimate derived from body height. Strength was normalized to weight (norm_strength1⁄4strength/weight). Muscle quality was evaluated by computing spec_strength (the primary analysis), and by the mean and standard deviation (SD) of the T1weighted thigh muscle MRI signal intensity (as a proxy of fatty infiltration). Cases and controls were compared using conditional logistic regression. Results: Of 179 knees with incident radiographic KOA, 113 were female (age 60.8, BMI 29.2) and 66 male (60.4; 29.4); of 195 non-incident knees, 113 were female (60.8, 27.0) and 82 male (59.4; 27.7). Quad spec_strength was found significantly (-12%) lower in incident vs. nonincident knees (Table 1). Quad strength (-7.1%) and norm_strength (-15%) were also significantly lower, quad CSA significantly greater (+6.5%), and the mean and SD quad MRI signal intensity greater (w5%, not significant) in incident vs. non-incident knees (Table 1). Similar relationships were observed in the flexors and adductors. In male knees, in contrast, the observed thigh muscle spec_strength was greater in incident than in non-incident knees, but the difference did not reach statistical significance. Conclusion: In women (but not in men), incident radiographic KOA is found to be associated with lower muscle strength per unit CSA (spec_strength) and per unit weight (norm_strength). Obesity, which is independently associated with incident radiographic KOA inwomen, may be associated with fatty infiltration of thigh muscles, and may cause an unfavourable ratio between loading and muscular stabilization of the knee. Our findings suggest that important relations of muscle function and risk of radiographic KOA exist and are detected with physiologically relevant measures of strength (i.e. specific strength). Quadriceps muscle status in incident and non-incident female knees Incident Non-incident