Arthrogryposis Multiplex Congenita in Pediatric Age: Correlation Between MUScular MRI and Functional Evaluation

Arthrogryposis multiplex congenita (AMC) is a group of rare diseases characterized by joint contractures at two or more distinct joint levels at birth. More than 400 causes are currently known. The prevalence is estimated at 1/3000 to 1/2000. Joint limitations are not progressive, but the functional consequences have a lifelong impact on patients.

Correlations between fibro-adipous infiltration and muscular deficits have already been studied in other neuromuscular diseases such as Pompe disease or Duchenne muscular dystrophy. These studies concluded on a good correlation between disease progression and severity, muscle strength, and fatty infiltration assessed by Mercuri score. The investigators concluded that muscular MRI can be used as a non-invasive biomarker and a tool to follow the progression of neuromuscular disease and help evaluate the potential effects of therapies.

The aim of this project is to define whether MRI could also be used as a tool, through the assessment of muscle fatty infiltration, to help predict the functional abilities of our patients with AMC, and more specifically the two most frequent types, Amyoplasia and distal arthrogryposis.

The investigators will analyze fatty infiltration measured by muscle MRI and quantify it using the MERCURI score which was developed by Mercuri et al. (Mercuri et al. 2002) as a semi-quantitative score to quantify fibro-adipose muscle infiltration on muscle MRI.

The investigators will evaluate musculoskeletal deficiencies and limitations of activity from data obtained from patients followed in our AMC reference center at the University Hospital Grenoble Alpes (CHUGA).

The investigators will include data from 220 children, 97 of whom have had a complete check-up including a muscle MRI. The investigators will study the existence of a correlation between this score and the deficiencies and limitations of activity.

The investigators will then evaluate the potential predictive role of fatty infiltration measured on MRI in the functional abilities of the patients.

This characterization will help to better determine and anticipate the functional capacities of our patients from the beginning of their treatment to improve their functional prognosis.

This initial work could enhance the reflection on the biomechanical modeling of joints and key functions such as standing and the acquisition of walking, in order to pave the way for rehabilitation and compensation methods that are better adapted to patient's needs.

Inclusion criteria

• age < 18 at the first clinical evaluation or follow up exclusively in CHUGA pediatric rehabilitation unit
• Clinical or molecular diagnosis of AMC established by geneticists at CHUGA
• functional evaluation during consultation and follow-up in CHUGA pediatric rehabilitation unit
• Muscle MRI of upper limbs, lower limbs and trunk performed at CHUGA pediatric radiology unit

Exclusion criteria

• Contra indication MRI.
• MRI non exploitable.
• Patient under guardianship or deprived of liberty