P.1.14 Knee extensor muscle force correlates with and may predict sit to stand ability in congenital muscular dystrophy

Abstract

Congenital muscular dystrophies (CMD) are early onset disorders of muscle associated with weakness and functional impairments. Two common subtypes are caused by mutations in the LAMA2 gene and Collagen VI genes (COL6a1, COL6a2, COL6a3) and present clinically as hypotonia and weakness, distal joint hyperextensibility (Collagen VI), progressive joint contractures, scoliosis, and often limited ambulation. Functional thresholds related to muscle force are limited in the literature and correlation between knee extension force or mobility and sit to stand ability in CMD are not established. We aimed to define the relationship between knee extension force and range with ability to stand from sitting, and to identify functional thresholds required to stand. We retrospectively analyzed data from 37 patients, aged 5–22, with Collagen VI or LAMA2-related CMD, assessed between 2010 and 2012. Age, gender, height, weight, knee extension force and range, and sit to stand scores of the Motor Function Measure were analyzed. Analysis showed strong Pearson correlation between mean knee extensor force (<i>r</i>=0.826 <i>p</i><0.001, <i>n</i>=37), and moderate correlation between knee extension range (<i>r</i>=0.522, <i>p</i>=0.0009, <i>n</i>=32) and sit to stand scores. Results also indicated 96% probability (<i>n</i>=22) of a sit to stand score of 0 (cannot stand up) for myometry measures below 40N, and 99% probability (<i>n</i>=14) for knee extension range less than −15°. Sit to stand correlation was greater with raw myometry [(N), <i>r</i>=0.826, <i>p</i><0.0001, <i>n</i>=37] versus normalized myometry [(%), <i>r</i>=0.770, <i>p</i><0.001, <i>n</i>=33)], indicating normalization may be inappropriate for this group due to varied effects of disease progression. Our data sample implicates a strong relationship between knee extension and standing ability in individuals with Collagen VI or LAMA2 CMD. Knee extension may be used to predict probability of sit to stand scores, with force <40N and range <−15° associated with inability to stand from sitting in this population.