Objective Greater quadriceps strength has been found to reduce risk for symptomatic knee osteoarthritis (SxKOA) and knee joint space narrowing (JSN). However, this finding could relate to muscle mass or activation pattern. The purpose of this study was to assess whether greater thigh muscle mass protects against (1) incident radiographic (RKOA), (2) incident SxKOA or (3) worsening of knee JSN by 30-month follow-up. Design Multicenter Knee Osteoarthritis (MOST) study participants, who underwent dual energy x-ray absorptiometry (DXA) at the Iowa site were included. Thigh muscle mass was calculated from DXA image sub-regions. Sex-stratified, knee-based analyses controlled for incomplete independence between limbs within subjects. The effect of thigh lean mass and specific strength as predictors of ipsilateral RKOA, SxKOA and worsening of JSN were assessed, while controlling for age, BMI, and history of knee surgery. Results A total of 519 men (948 knees) and 784 women (1453 knees) were included. Mean age and BMI were 62 years and 30 kg/m2. Thigh muscle mass was not associated with risk for RKOA, SxKOA or knee JSN. However, in comparison with the lowest tertile, those in the highest and middle tertiles of knee extensor specific strength had a lower risk for SxKOA and JSN (OR 0.29–0.68). Conclusions Thigh muscle mass does not appear to confer protection against incident or worsening knee OA. These findings suggest that future studies of risk for knee OA should focus on the roles of knee extensor neuromuscular activation and muscle physiology, rather than the muscle mass.

Objective To determine the test-retest reliability of knee joint space width (JSW) measurements made using standing CT (SCT) imaging. Subjects and Methods This prospective two-visit study included 50 knees from 30 subjects (66% female; mean ±SD age 58.2 ± 11.3 years; BMI 29.1 ± 5.6 kg/m2; 38% KL grade 0–1). Tibiofemoral geometry was obtained from bilateral approximately 20° fixed-flexed SCT images acquired at visits two weeks apart. For each compartment, the total joint area was defined as the area with a JSW <10mm. The summary measurements of interest were the percent of the total joint area with a JSW less than 0.5mm thresholds between 2.0mm–5.0mm in each tibiofemoral compartment. Test-retest reliability of the summary JSW measurements was assessed by Intraclass Correlation Coefficients (ICC 2,1) for the percent area engaged at each threshold of JSW and root-mean-square errors (RMSE) were calculated to assess reproducibility. Results The ICC were excellent for each threshold assessed, ranging from 0.95–0.97 for the lateral and 0.90–0.97 for the medial compartment. RMSE ranged from 1.1–7.2% for the lateral and from 3.1–9.1% for the medial compartment, with better reproducibility at smaller thresholds of JSW. Conclusion The knee joint positioning protocol used demonstrated high day-to-day reliability for SCT 3D tibiofemoral JSW summary measurements repeated 2 weeks apart. Low-dose SCT provides a great deal of information about the joint while maintaining high reliability, making it a suitable alternative to plain radiographs for evaluating JSW in people with knee OA.

Objective. To determine the degree to which focally elevated tibiofemoral joint contact stress is reduced by using a frontal plane realigning brace. Methods. Fifteen volunteers (9 women) with unicompartmental tibiofemoral osteoarthritis underwent weight-bearing radiographic imaging at 15-208 and 5-108 of knee flexion with and without an UnloaderOne knee brace. Discrete element analysis was used to estimate compartment-specific contact stress distributions. Paired t-tests were used to assess the differences in mean contact stress and contact stress distributions, comparing the braced and unbraced conditions. Results. The mean 6 SD age was 56.1 6 6.4 years and body mass index was 28.4 6 4.5 kg/m 2 . Twelve of 15 participants were fit with braces set to unload the medial compartment. For the 15-208 condition, the mean contact stress in the compartment of interest did not significantly change (0.08 6 0.35 MPa; P 5 0.410). Also at 5-108 flexion, the mean contact stress in the compartment of interest did not significantly change with use of the brace (0.24 6 0.45 MPa; P 5 0.175). Conclusion. This is the first study of the effects of a frontal plane realignment brace on in vivo articular contact stress in native human knees. Using the off-the-shelf brace tested, there were no changes in compartmental tibiofemoral contact stress distributions at either 15-208 or 5-108 of knee flexion, revealing no redistribution of contact stress away from the compartment of interest. These findings indicate that the brace that was studied was ineffective for redistributing tibiofemoral contact stress. Further research is necessary to determine whether double-upright or customized frontal plane braces are effective in redistributing compartmental articular contact stress.

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