A 51-year-old man underwent surgery for removal of a carcinoma on his trachea . After surgery , he suffered excessive nervousness , muscle cramps , and spasmodic skeletal muscle contractions in his arms , legs , and feet . Laboratory tests revealed markedly low levels of calcium in his blood . Treatment with intravenous calcium and vitamin D led to recovery in a few weeks . Which one of he following conditions is responsible for these symptoms in this patient following surgery ?