Résumé :
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Ankle strength is one of the functions primarily affected in several neuromuscular disorders such as Charcot-Marie-Tooth disease or Myotonic Dystrophy type 1. In order to accurately follow the evolution of the disease and quantify effects of new therapies on this particular function, it is essential to have a device enabling to accurately and reliably measure both ankle dorsiflexion and plantarflexion strength. A new dynamometer has been developed to measure the isometric torque generated around the ankle joint. The device is designed with two load cells on which the subject applies strain through a strap. The nominal force measured by the device is 200 daN with a precision of 0.1 daN. The objectives of the study were to validate the reliability of the device, to establish norms and predictive equations on a population of healthy subjects. 346 healthy subjects aged from 5 to 80 years old were included. Subjects performed several trials to achieve their maximal voluntary isometric contraction for dorsiflexion and plantarflexion measurements on each side. The level arm between the ankle joint and the force application point was recorded to deduce a measurement of torque. A retest session was performed by 78 subjects. The applicability to weak patients was tested on several patients suffering from various neuromuscular disorders.The intraclass correlation coefficients were 0.94 for dorsiflexion measurements and 0.88 for plantarflexion measurements with a coefficient of variation of 11% between test and retest session for both functions. Norms were established separately for men and women. Predictive equations were established separately for children and adults. Height was the main predictor of strength for children using a polynomial model. For adults, ankle torques were best predicted by height, sex and, age. In conclusion, the developed dynamometer was proven to be reliable, able to measure both ankle dorsiflexion and plantarflexion from a wide range of values (from 2 to 200 Nm). Its usability for weak patient added to the norms and predicted models presented should enable its use to accurately assess deficit ankle dorsiflexion and plantarflexion torques in neuromuscular disorders.
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