The purpose of this retrospective work is to study the consequences of obstetrical brachial plexus paralysis on the rotator muscles of the shoulder. First of all, the investigators want to study the reproducibility of the isometric contraction forces of the rotator muscles of the shoulder thanks to an isokinetic dynamometer. The investigatorsthen want to compare the measurements obtained from the paralyzed side compared to the healthy side. The preoperative MRI performed will be studied in search of amyotrophy. These data will be compared with those of the isokinetic assessment to identify children requiring muscle transfer of reinforcement of the external rotator muscles.

Obstetrical brachial plexus palsy is caused by arm stretching at birth. Recovery is not complete in a third of cases. The main sequelae is a decrease in the mobility in external rotation (ER) of the shoulder at the clinical examination. This is attributed to an imbalance between the deficient external rotator muscles (mainly infraspinatus), and the internal rotator muscles (subscapularis, pectoralis major, latissimus dorsi). A stiffness would appear because of the permanent vicious attitude of the shoulder. There is a surgical indication for arthroscopic retraction before the age of 2 years. A muscle transfer to strengthen the shoulder RE can be performed secondarily from the age of 3 years in case of persistent sequelae but the investigators lack of objective elements to ask this indication.

1. Study of the reproducibility of the isometric contraction forces of the internal and external rotator muscles obtained by isokinetic apparatus in paralyzed children.

   The isokinetic device is the gold standard for assessing muscle strength. The reproducibility of Peak Torque (PT) and Total Work (TT) will be analyzed in paralyzed children aged 3 to 5 years.

2. Comparison of isometric contraction forces of internal and external rotator muscles obtained by isokinetic device in a group of POPB children.

   Inclusion criteria: patients with obstetrical brachial plexus palsy aged between 3 and 5 years. Investigation of a significant difference in PT and TT with respect to ER and IR on the paralyzed side compared to the healthy side.

3. MRI analysis of muscular atrophy of the shoulders of paralyzed patients. The absence of recovery induces a deformation of the known shoulder joint with criteria to quantify it, but muscular amyotrophy has never been studied on the MRI of patients with brachial plexus palsy. Analysis of bilateral shoulder MRI of paralyzed patients (performed at 1 year of age as part of systematic follow-up if no-shoulder ER): describe and quantify muscle amyotrophy by measuring muscle thickness compared to healthy contralateral side. Index <0.5 in favor of amyotrophy, look for a positive correlation between the presence of muscular atrophy and joint deformity of the shoulder.

4. What are the predictive factors for recovery of external and internal shoulder rotators of children with brachial obstetrical plexus palsy?

By correlating the results of projects 1 to 3, it would be possible to:

• to identify the favorable or unfavorable prognostic factors of shoulder recovery of paralyzed children.
• identify patients with early signs of muscle recovery that do not require muscle transfer.

Perspectives: change of the therapeutic algorithm

• modification of the surgical technique according to the analysis of amyotrophy on the MRI: if subscapularis amyotrophic, more extended release with section of its upper fibers to mitigate its harmful effect on the development of the shoulder
• not to make unnecessary muscle transfer in patients with recovery of external rotator muscles masked by subscapularis fibrosis. Transfer performed if necessary secondarily according to the testing of muscular strength at the age of 3 years by isokinetic device.

Inclusion criteria:

- children with obstetrical brachial plexus palsy

Exclusion criteria:

- other neurological disorders, post-traumatic shoulder stiffness

children with obstetrical brachial plexus palsy

NC