The investigators are studying the ability of a novel rapid magnetic resonance imaging (MRI) protocol to provide more accurate and earlier information about whether an infant with brachial plexus birth palsy will require nerve surgery.

Brachial plexus birth palsy (BPBP) affects approximately 1 in 1,000 newborns, and though the majority of infants regain full function of the affected arm without nerve surgery, those with more severe nerve root injuries will require it. Currently, the best way to determine who will need surgery is to measure the trajectory of muscle recovery by serial clinical exams, but the optimal time for nerve surgery (before 3 months of age) is earlier than the time it usually takes to determine whether the infant needs surgery (up to 6 months.) A non-invasive diagnostic test that identifies the more severe injuries that require surgery earlier than serial exams would improve treatment timing, planning, and accuracy, and ultimately outcomes.

The investigators have developed a rapid MRI sequence with high spatial resolution and soft tissue contrast that does not require sedation or injection of a contrast agent, and that appeared to accurately assess the severity of nerve injury in infants with BPBP in a pilot study. This pilot study demonstrated that the protocol distinguishes infants who ultimately needed surgery from those who recovered spontaneously. The purpose of the current study is to enroll 100 infants at 3 centers (Shriners Hospital for Children Northern California, Boston Children's Hospital, and Gillette Children's Hospital) over a 5 year period to validate this imaging protocol as the new "gold standard" to determine whether infants with BPBP need surgery, so that individuals who need it could have surgery earlier when it is more effective, and the parents of the majority who will recover spontaneously could be spared months of worry.

Inclusion Criteria:

• Diagnosis of brachial plexus birth palsy.
• Age at consent ≤4 months

Exclusion Criteria:

• Bilateral brachial plexus birth palsy.
• Age at MRI <28 days or >4 months old (patients can be enrolled prior to 28 days of age, but the imaging must occur in the 28 days to 4 months' time period). The lead PI will need to approve the enrollment of a subject who will have the MRI after 90 days of age.
• Concomitant medical conditions that would preclude performance of or confound interpretation of MRI or any clinical assessment.

This is a multicenter prospective cohort study of patients with BPBP. The study takes place at Shriners Hospitals for Children - Northern California, Boston Children's Hospital, and Gillette Children's Specialty Healthcare. All infants with BPBP between 0 and 12 weeks of age who present for treatment to a participating site will be offered participation in this study. Those infants with concomitant birth injuries that would make positioning in the MRI scanner difficult or painful (such as a birth humerus or clavicle fracture) will have their enrollment deferred. If the injury heals and the MRI can be performed within the required age range, they may be included in the study. If not, they will be excluded. Those infants who attempt to complete or actually complete the MRI scan but end up with unusable images will continue to be followed clinically, but will be removed from participation in this study.

Data will be coded and stored in a secured locked office. PHI will not be reused or disclosed to any other person or entity, except as required by law or for authorized oversight of the research project. Any disseminated data will be aggregated and coded.