By the placement of screws through the lateral articulations, rigid internal fixation can be secured in the lumbar spine-fusion operation. The position in which the joint is to be ankylosed can be accurately controlled, and the necessity for prolonged immobihization in plaster is eliminated. Forty (90 per cent.) of forty-four patients operated upon have solid bony fusion after two to seven years. The osseous fusion develops slowly while the patient is ambulatory.