A contracture of the sternocleidomastoid muscle on one side causes the child’s head and neck to be tilted to that side, which is called pediatric myoclonus. The term “muscular” refers to the muscle (sternocleidomastoid) that causes the condition. The muscle is shortened, tense and thickened. The sternocleidomastoid muscle is the muscle that starts at the sternum and clavicle and ends at the mastoid process. When you turn your head to one side, the triangular shape of the muscle that appears on the opposite side of the neck is the sternocleidomastoid muscle, which is an important component of the muscle that maintains the position of the neck, so once the sternocleidomastoid muscle is contracted on one side (as a result, the muscle is shortened, tense and thickened), it can cause pediatric myotonic squint. The typical clinical presentation of pediatric myotonic squamous neck is the appearance of a mass in the neck, usually around 2-3 weeks after birth, located in the middle or lower part of the sternocleidomastoid muscle, together with the muscle. Some parents sometimes mistake the lymph nodes in the neck for lumps, which are actually different. The lymph nodes in the neck are located under the skin, are the size of a soybean, and have no relationship with the muscle, while the masses in congenital myotonic squamous neck occur in the sternocleidomastoid muscle and are not particularly isolated, some are pike shaped, some are oval shaped, and some are simply localized thickening of the muscle. In the muscle masses of congenital myotonic squamous neck, the child has no painful sensation and no discomfort to touch. The lump gradually disappears and dissipates around 2-6 months. In addition to the muscle mass, the sternocleidomastoid muscle on the affected side is thickened to touch, tense and shortened, thus pulling the head toward the affected side while the child’s jaw is turned toward the healthy (opposite) side. Some parents are sometimes confused about the child’s tilt and would like to think about it carefully, as it should not be difficult to understand and needs to be understood correctly, as it is a matter of adopting the right treatment. Which side of the child’s head is tilted to is called the tilt of the neck, not which side the child’s jaw is turned to. For example, if the child’s head is tilted to the right and the jaw is turned to the left, it is called congenital right-sided myotonic squint. Congenital myotonic squint needs to be treated promptly, and if not treated promptly, secondary deformities can occur. For example, asymmetry of the cheeks (commonly known as “big and small face”), which causes visual fatigue, etc. If the facial asymmetry is prolonged, even after treatment, it is difficult to recover the deformity. The causes of congenital myotonic squint are not well understood and the preventive measures are not clear.