Stress Changes in Intervertebral Discs of the Cervical Spine After Partial Fusion

A detailed and validated 3D FE model of human cervical spine (Sadegh et al. 2000) was altered to simulate partial fusion. Five single level partially fused new models, one at each disc level, were used to study the change in stresses in adjacent levels. Two cases of partial fusion, 80% and 60% were considered. The fused models were loaded with a 50 N compressive pre-load and with a 1.5 Nm moment in flexion, extension, lateral bending and axial rotation. The previously obtained results of the unfused model (Tchako et al. 2002) and of the fused models were used to study the change in stresses in adjacent levels. The results indicate that, in general, there are stress changes as high as 94%, depending on the loading mode and location, in adjacent discs after discectomy and fusion. However, the difference between the stress change of 80% and 60% of partial fusion is insignificant.