P15.2: Sternomastoid injury due to birth injury

On each side of the neck there is a head-turning muscle that we use to tilt and turn our head to the side. If the head-turning muscle gets tight on one side, it pulls your head over to that side. At the same time, your face turns slightly to the opposite side. If the head-turning muscle gets tight on both sides at the same time, the head will tilt backwards.

The child is subjected to great pressure during a vaginal birth. This pressure is necessary for the child to be born through the pelvis and the vagina. The pressure, plus the narrow birth canal, can damage the child’s head-turning muscle. Damage can particularly occur if, for example, the child is born from an unusual position in the womb. Using a forceps can also damage the head-turning muscle. There may also be a congenital shortening of the head-turning muscle. The head's mobility is then restricted and the muscle can get damaged during the birth.

The muscle may get torn, for example. Blood can then collect in the muscle tissue. This is called a hematoma. It is also possible that the blood supply to the muscle during the birth is insufficient and that this causes damage. When the head-turning muscle is damaged, it can feel hard and thick. After being damaged, the head-turning muscle can get shorter. The child does then not hold its head up straight and is unable to move its head in every direction as is usual.