| Summary: | Degenerative disc disease (DDD) is a natural degenerative process that affects the intervertebral discs of the spine and is a major cause of lower back pain. After failure of conservative measures DDD may be treated surgically by fusion or Total Disc Replacement (TOR). Fusion results in loss of motion at the operated level, causing increased motion at adjacent levels. This is thought to accelerate further degenerative changes. The intention of TOR is to replace the disc and maintain normal motion in the spine. CAdisc-L is a novel TOR implant; it preserves motion by deforming under load rather than articulating like existing devices. The objective of the study was to ascertain the effect of implantation of CAdisc-L on sagittal biomechanics. Spine specimens were tested before and after implantation to asses implant stiffness, range of motion and stability. Additionally the position and migration of the Instantaneous Axis of Rotation (IAR) of the specimens was recorded. Finally, the ultimate failure load of implanted specimens in compression was evaluated. Monosegmental cadaveric spine specimens were used for the study. Loads and moments were applied by a uni-axial test machine and movement of the specimen was captured using reflective markers and a motion tracking camera. Implantation resulted in a reduction in compressive stiffness, but an increase in overall disc height which maintained the intervertebral space in compression up to 4.4kN. A reduction in flexural stiffness was seen after implantation as well as a reduction in neutral zone. Tracking of the IAR of the specimen indicated that it migrated by a similar range to intact specimens both horizontally and vertically. The position of the IAR was displaced posteriorly my 5.2mm at 6° of flexion compared to intact specimens. Ultimate failure loads were not found to be affected significantly.
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