Radiography and biomechanics of sixth and seventh cervical vertebrae segments after disc fenestration and after insertion of an intervertebral body spacer. A canine cadaveric study.

Objectives: To study the radiographic characteristics and the biomechanical properties of the sixth and seventh cervical (C6–C7) vertebral motion unit (VMU) with an intact disc, after disc fenestration, and after placement of an intervertebral body spacer (IVBS). Methods: Six cadaveric C6-C7 VMU were retrieved from six Greyhound cadavers. Each VMU was loaded at 3 Nm of torque sequentially in flexion, extension, and in right and left lateral bending. The range-of-motion (ROM) was measured with a Zebris 3D® system. The intervertebral disc cross-sectional area was measured on lateral and ventro-dorsal radiographs. Biomechanical testing and radiographic measurements were performed with an intact disc, after disc fenestration, and after IVBS placement. Data were reported as mean ± SD. Results: The intervertebral disc cross-sectional area was significantly decreased after disc fenestration and increased after IVBS placement, but remained significantly smaller than the area of intact disc in some of the tested conditions. The ROM with an intact disc, after disc fenestration and after IVBS placement, in flexion were 11.5° ± 1.0, 15.2° ± 2.3, and 10.9° ± 4.7, respectively, and in extension were 15.6° ± 3.7, 24.7° ± 6.2, 21.9° ± 4.0, respectively. There was a significant increase in extension ROM after disc fenestration. Intervertebral body spacer placement significantly decreased ROM in flexion but ROM in extension was not different from disc fenestration. No significant changes in lateral bending ROM were detected. Clinical significance: The use of an IVBS reduced disc space collapse but did not restore stability of the VMU to normal values in extension after cervical disc fenestration.