Tetanus often begins with mild spasms in the jaw muscles (lockjaw). The spasms can also affect your chest, neck, back, and abdominal muscles. Back muscle spasms often cause arching, called opisthotonos.
Sometimes the spasms affect muscles that help with breathing, which can lead to breathing problems.
Prolonged muscular action causes sudden, powerful, and painful contractions of muscle groups. This is called tetany. These episodes can cause fractures and muscle tears.