Investigation of the Relationship Between Shoulder Alpha Angle and Humeral Head Displacement Percentage Measured by Ultrasonography in Neonatal Brachial Plexus Palsy Infants With Clinical Parameters

Infants aged 3 months to 1 year with neonatal brachial plexus injury (Narakas Group I-III) will be evaluated at a single pediatric rehabilitation clinic. At each visit, the same physiatrist will perform a standardized clinical examination, including assessment of demographic and obstetric history, subluxation-specific clinical signs (axillary skin fold asymmetry, palpable posterior fullness), passive range of motion, upper extremity length discrepancy, the Active Movement Scale, and the Toronto Test Score. A second physiatrist, blinded to clinical findings, will perform shoulder ultrasonographic evaluation using a posterior approach to measure the alpha angle and the percentage of humeral head displacement (PHHD). Glenohumeral subluxation will be defined as an alpha angle greater than 30 degrees; dislocation will be defined as an alpha angle greater than 30 degrees combined with PHHD greater than 50%. Associations between clinical findings and ultrasonographic subluxation will be analyzed using Generalized Linear Mixed Models to account for repeated measurements per patient, followed by ROC curve analysis to identify optimal predictive thresholds.

Inclusion criteria

• Diagnosis of neonatal brachial plexus injury (NBPI) between 3 months and 1 year of age
• Narakas classification Group I, II, or III
• Absence of nerve root avulsion

Exclusion criteria

• Prior shoulder surgery for NBPI
• Inability to tolerate ultrasonographic examination
• Concomitant musculoskeletal (e.g., torticollis, humeral fracture) or neurological disease
• Bilateral NBPI
• Narakas classification Group IV
• Botulinum toxin injection to the affected shoulder