Muscle and joint elastic properties during elbow flexion in Duchenne muscular dystrophy

Abstract

Duchenne muscular dystrophy (DMD) is characterized by a direct effect on muscle fibres leading to muscle atrophy and weakness due to a lack of muscle dystrophin. Dystrophin is a sarcolemma cytoskeletal protein whose deficit leads to segmental necrosis of the muscle fibre. DMD is thus characterized by a decrease in the number of muscle fibres, which are progressively replaced by fibroadipose tissue. The first observed clinical signs relate to difficulties in running or climbing stairs and calf hypertrophy. Gait then becomes lordotic and waddling. Between 6 and 11 years of age, limb and torso muscles progressively and steadily decrease in strength. Loss of ambulation occurs (average 10.5 years of age) and all torso and limb muscles decrease in size.The assessment of muscle mechanical properties in DMD patients is mostly limited to a more or less sensitive evaluation of strength production, generally in static conditions and occasionally during a locomotor act. Two kinds of non-invasive technique are generally used to characterize muscle functional properties in DMD patients. (i) Semi-quantitative measurements (manual testing, timed scores during motor acts) are performed in routine clinical practice and afford a functional evaluation (Edwards & Hide, 1977;Brooke et al. 1981;Aitkens et al. 1989). For instance, manual testing (scored from 0 to 5) is based on an international graduated scale of muscle ability: MRC scale (Medical Research Council, 1943) reorganized from 0 to 10 (Brooke et al. 1981).(ii) Quantitative measurements (manual dynamometry) can be performed in some muscle groups and give a maximal voluntary contraction (MVC) measurement (Munsat, 1989).Understanding of the mechanisms responsible for muscle adaptation to altered functional demand (pathology or training) requires quantification of muscle mechanical properties. For instance, muscle contractility and muscle elasticity were experimentally found to be sensitive to periods of hyperactivity as well as hypoactivity (Goubel & Marini, 1987; Almeida Silveira et al. 1994;Canon & Goubel, 1995 1. Maximal voluntary contraction (MVC), series elastic stiffness and total joint stiffness during elbow flexion were investigated in healthy boys and in boys with Duchenne muscular dystrophy (DMD) in order to assess changes in mechanical properties induced by the disease.2. Two methods were used to perform stiffness measurements: (i) the application of sinusoidal perturbations to the joint during flexion efforts, allowing the calculation of total joint stiffness; (ii) the use of quick-release movements of the elbow, which had previously been maintained in isometric contraction, allowing the calculation of series elastic stiffness. In each case, stiffness was linearly related to torque, leading to the calculation of a normalized stiffness index as the slope of this stiffness-torque relationship.3. As expected, mean MVC was found to be much higher for healthy boys (20.02 ± 5.20 N m) than for DMD patients (3.09 ± 2.44 N m). Furthermore, the results showed that it was poss...

New insights on contraction efficiency in patients with Duchenne muscular dystrophy

“…Together, this may contribute to the increased muscle-tendon stiffness reported in humans during quick release movements (7). Using a more direct assessment of stiffness, we found a significant higher BB muscle stiffness in DMD patients compared with healthy controls [2 times higher when the muscle was stretched (Lacourpaille et al, unpublished observations)].…”

An investigation into the variability between different shear wave elastography systems in muscle

“…ICC (1,1) was used for intra-system reliability, whilst ICC (3,1) was used for inter-system reliability; it was assumed that a single acquisition rather than a mean of repeated acquisitions would be used in clinical practice.…”

“…The mechanical properties of muscles can be altered by a range of pathologies, such as muscle dystrophy [1], spasticity [2], and inflammation [3]. Muscle stretch and contraction elastic elements are major determinants of muscle function and efficient locomotion [4,5].…”

Reliable Protocol for Shear Wave Elastography of Lower Limb Muscles at Rest and During Passive Stretching

“…Quick-release method (Cornu et al, 2001) has been investigated to evaluate the elasticity of muscle-tendon unit. This technique cannot isolate the behavior of one muscle and it is difficult to apply on pathologic subjects, due technical difficulties of performing the test on pathological subjects with high joint stiffness or bone deformities.…”