It was decided to change the study from a cohort to a randomized controlled trial.

This study evaluates the ability of a newly designed splint called "Sup-ER Splint" to improve the arm function and anatomy of children with birth related brachial plexus injuries.

The brachial plexus is a group of 5 nerves from the spinal cord that provide the movement and sensation of an upper extremity. In some difficult deliveries, traction on the shoulder may lead to damage to the brachial plexus and will result in an arm that is paralyzed. This is called 'birth related brachial plexus injury' (BRBPI). This may occur in up to 1/1000 births and the nerves may be injured minimally to severely. About 2/3 of children with this injury will recover to quite functional levels simply by maintaining looseness of joints while their nerves slowly heal. Some children have nerve injuries severe enough that they require surgical reconstruction with nerve grafts and nerve transfers to achieve even adequate function. One almost universally common outcome, even in children with otherwise "good" recovery, is that the motions of external rotation of the shoulder and supination of the forearm are weaker, later to recover, and often incomplete. Even beyond these direct functional weaknesses, because the arm is positioned poorly, joint contractures and imbalance of these motions can interfere with other upper extremity movements like elbow flexion, even when elbow flexion itself is well recovered. More importantly, lack of full motion leads to long term changes in the structure, growth, and posture of the shoulder requiring further musculoskeletal surgery, or a child with permanent deformity or disability. Surgery cannot completely correct this deformity. Any gains in active and passive range of motion during the first year of life may improve these long-term shoulder outcomes. The investigators have instituted a program of early passive repositioning mostly using a custom Sup-ER (Supination and External Rotation) splint during early growth and development to improve arm position and range of motion where ER and Sup are weak. In compliant patients in a pilot study, the speed and strength of recovery of ER and Supination are improved compared to historical controls. It is a novel splint and protocol designed by the investigators and has significantly changed the care received by patients in BC. This study will evaluate the use of Sup-ER splint in multiple centres over a five year period by assessing the arm function at common time points in recovery.

Inclusion Criteria:

• Diagnosis of brachial plexus injury at birth.
• Significant deficit in external rotation and/or supination of the affected limb based on clinical assessment using the Toronto Active Movement Scale at 6 weeks of age: External Rotation ≤ 2 and/or Supination ≤ 2
• Tightness in Passive Range of Motion of external rotation: any angle of less than 180°.
• Age 6-8 weeks for complete protocol fulfillment.

Exclusion Criteria:

• Neuromuscular disorder.
• Unwillingness or inability to comply with the requirements of this protocol.