Erb Palsy

Which of the following muscle groups is primarily affected in a typical case of Erb's palsy, leading to the characteristic adducted and internally rotated shoulder posture?

A newborn presents with an adducted, internally rotated shoulder, extended elbow, and pronated forearm. This classic 'waiter's tip' deformity is most commonly associated with injury to which of the following nerve roots?

A 3-day-old infant is diagnosed with Erb's palsy. Which of the following is the most common obstetric risk factor associated with this condition?

A 2-month-old infant with a suspected Erb's palsy shows no signs of recovery with conservative management. What is the most appropriate initial diagnostic investigation to assess the extent of nerve injury and guide further management?

A 6-month-old infant diagnosed with Erb's palsy at birth shows persistent weakness in shoulder abduction and external rotation, despite consistent physical therapy. What is the most critical factor influencing the decision for surgical intervention in such a case?