Acute deformity correction of lower extremities under SSEP-monitoring control

Intraoperative somatosensory evoked potential (SSEP) monitoring was performed in eight children who had undergone an acute deformity correction in the lower extremities using external fixation. Five patients showed stable evoked potentials during surgery and had no neurologic complications postoperatively. Three patients experienced evoked potential abnormalities. In one patient, 60 degrees external rotation of the foot produced significant SSEP changes. The reduction of rotation to 40 degrees resulted in tibial but not peroneal SSEP recovery. Peroneal nerve deficit was noted postoperatively. The second patient showed substantial SSEP attenuation after 45 degrees correction of distal tibial valgus. However, spontaneous recovery of the response occurred, which allowed maintenance of the achieved correction. In a third patient, significant SSEP changes occurred after 90 degrees external rotation and 10 mm medial translation of the distal femur. Total release of translation allowed 75 degrees external rotation without SSEP abnormalities. Neither of the latter two patients had peripheral nerve deficits postoperatively. Intraoperative SSEP monitoring thus helps to define a neurologically safe limit of acute deformity correction.