Biomechanical stability of lower cervical spine immediately after discectomy with grafting

Anterior cervical discectomy is commonly used to treat radiculopathy and myelopathy. Although the size of the implanted graft may influence the clinical outcome of anterior reconstruction of the cervical spine, the ideal graft height remains arguable. The objective of the current study was to study the interrelations of graft height and immediate biomechanical stability in an anterior cervical discectomy model.

Six fresh-frozen human cadaver cervical spines (C1-T1) were tested in five sequential states. The first state tested was the "normal" state (specimens with intact discs). The other four states were tested after C5-C6 discectomy by the Smith-Robinson graft technique, using graft thicknesses of 100%, 120%, 140%, and 160% of the baseline height. The baseline height was defined as the intervertebral disc height of C5-C6 at the intact stage. Intervertebral segment flexion, extension, bending and rotation of C5-C6 were recorded using a 3D laser scanner and analyzed using Geomagic Studio 5.0 software.

Bone grafting at 100% baseline height after discectomy provided the least stability and the greatest movement range. With increasing height of grafts, the movement range of the cervical spine declined. Immediate stability of the operated segments was significantly increased by grafting with 140% and 160% baseline heights compared to the baseline height condition.

Strut-graft with appropriate distraction after Smith-Robinson anterior cervical discectomy plays an important role in the whole immediate biomechanical stability of the lower cervical spine. A graft height of 40% greater than baseline may be ideal after single discectomy in clinical practice.