Justin Pol, Christopher McLouth, Mariana Jacobs, Mary Sheppard, Michael A. Samaan. University of Kentucky, Lexington, KY.

BACKGROUND: Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder that negatively impacts the musculoskeletal system. Previous work has shown decreased quadricep/hamstring strength in people with MFS compared to healthy individuals. However, the impact of MFS on activities of daily living such as a sit-to-stand (STS) are not well understood. The purpose of this study was to evaluate joint loading in people with MFS during a STS task. We hypothesize that people with MFS will perform the STS task with abnormal knee joint loading. METHODS: Ten people with MFS (20 limbs, 9F, age:36.5±7.54 yrs) were age, sex and BMI-matched to 10 healthy asymptomatic individuals (20 limbs, 9F, age:29.5±7.34 yrs). Participants were asked to perform 5 repetitions of the STS task at a self-selected pace starting from a seated position. Peak internal hip, knee and ankle joint extensor moments (Nm•kg-1), the total support moment (TSM; Nm•kg-1) and the hip, knee and ankle joint percent contributions to the TSM during the STS task were assessed. In order to account for the correlation between right and left limbs (bilateral samples), a linear mixed model was used to assess group differences in lower extremity joint loading parameters (p<0.05). RESULTS: Compared to healthy individuals, people with MFS exhibit 1.12x higher peak ankle plantarflexor moment (p=0.002), 1.34x higher TSM (p=0.002), 6.3% less hip contribution to TSM, and 9.6% higher ankle contribution to TSM (p=0.007). No differences were observed in hip and knee joint moments or the percent knee joint contribution to the TSM (p>0.05). CONCLUSIONS: People with MFS perform the STS task utilizing altered joint loading patterns compared to healthy individuals. The overall increase in TSM in people with MFS indicates a higher lower extremity muscular demand to successfully perform the STS task. In order to successfully perform the STS task, the MFS group utilized a larger ankle joint contribution to the TSM and higher plantarflexor moment to compensate for the lower hip joint contribution to the TSM. Our study results suggest altered lower extremity mechanics during a STS task in people with MFS that may be associated with abnormal hip and ankle muscle function. Future work will focus on understanding the role of the hip and ankle joint musculature on lower extremity joint loading patterns in people with MFS.

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