Influences of different lower cervical bone graft heights on the size of the intervertebral foramen: multiple planar dynamic measurements with laser scanning

The aim of this study is to evaluate the influences of different bone graft heights on the size of the intervertebral foramen, which will help determine the optimal graft height in clinical practice. Six fresh adult cadavers were used, with the C5-C6 vertebral column segment defined as the functional spinal unit (FSU). After discectomy, the C5/6 intervertebral height was set as the baseline height (normal disc height). We initially used spiral computed tomography (CT) to scan and measure the middle area of the intervertebral foramen when at the baseline height. Data regarding the spatial relationship of C5-C6 were subsequently collected with a laser scanner. Grafting with four different sized grafts, namely, grafts of 100, 130, 160, and 190% of the baseline height, was implanted. Moreover, we scanned to display the FSU in the four different states using Geomagic8.0 studio software. Multiple planar dynamic measurements (MPDM) were adopted to measure the intervertebral foramen volume, middle area, and areas of internal and external opening. MPDM with a laser scanner precisely measured the middle area of the intervertebral foramen as spiral CT, and it is easy to simulate the different grafts implanted. With the increase of the bone graft height, the size of the intervertebral foramen began to decrease after it increased to a certain point, when grafts of 160% of the baseline height implanted. MPDM of the intervertebral foramens with laser scanning three-dimensional (3D) reconstitution are relatively objective and accurate. The recommended optimal graft height of cervical spondylosis is 160% of the mean height of adjacent normal intervertebral spaces.