Lumbar spinal fusion using the Diapason system

Lumbar spinal fusion with the Diapason system was performed on 58 patients at Toho University Ohmori Hospital from November 1991 to November 1994. The first 44 consecutive patients were followed for more than 1 year, including 34 cases with degenerative diseases. Those 34 cases consisted of 22 men and 12 women, ages 19-78 years (average 47.4), with 49 vertebral levels; these patients were followed for an average of 26.3 months. The clinical improvement and rate of bony union after 1 year of surgery were examined and the intervertebral angulatory motion degree of fused vertebrae was measured using a radiographic functional photo image during 1 year. We also performed an experimental study to evaluate the rigidity of this system. There were no severe complications. Although there was no instrument breakage or screw migration, two cases of rod migration were observed in L5-S1 arthrodesis. A mean improvement rate of 84.3% in the Japanese Orthopaedics Association (JOA) score was revealed. Thirty-three of 34 (97.1%) patients demonstrated successful arthrodesis after their initial procedure. In 10 segments (20.4%) 3-5 degrees of angulatory mobility were still retained, and no angulatory motion was observed in 27 segments (55.1%) 3 months after the surgery; however, no angulatory motion was observed in 44 segments (89.8%) 1 year after the surgery. In our biomechanical study, we observed that the anterior intervertebral space became narrow and mobile with loading, but when the loading was removed, the space reverted to the initial site. This movement was thought to be due to a certain elasticity in the rod and screw, and not loosening at the connection level. This system was evaluated based on the results of both clinical and biomechanical study. Notwithstanding the fact that this method has been evaluated as semirigid fusion, it does provide satisfactory bony union in posterolateral fusion, with excellent clinical results.