A 3-month-old male infant is brought to the pediatric clinic by his parents due to persistent tilting of his head to the right side since birth. The parents noticed that the baby prefers to look to the left and has difficulty turning his head to the right. They are also concerned about a small lump in his neck and slight flattening of the back of his head on the right side. The baby was born full-term via vaginal delivery after a prolonged labor. The pregnancy was otherwise uneventful. No complications were noted at birth, and the baby has been feeding and developing well. There is no family history of neck or musculoskeletal abnormalities. On examination, the infant’s head is tilted to the right with the chin rotated to the left. A firm, non-tender, 2 cm mass is palpated along the right sternocleidomastoid (SCM) muscle. Passive range of motion of the neck is limited, with resistance to rotation toward the right side. There is mild right-sided plagiocephaly noted, with flattening of the occiput on the right side. What is the first-line treatment for this condition?
