Study design: A new artificial intervertebral disc was developed, and its intrinsic biomechanical properties, bioactivity, and the effectiveness as a total disc replacement were evaluated in vitro and in vivo.
Objectives: To introduce a new artificial intervertebral disc and to evaluate the in vitro mechanical properties, fusion capacity to bone, and segmental biomechanics in the total intervertebral disc replacement using a sheep lumbar spine.
Summary of background data: The loss of biologic fusion at the bone-implant interface and prosthetic failures have been reported in previous artificial discs. There have been no clinically applicable discs with detailed experimental testing of in vivo mechanics and interface fusion capacity.
Methods: The artificial intervertebral disc consists of a triaxial three-dimensional fabric (3-DF) woven with an ultra-high molecular weight polyethylene fiber, and spray-coated bioactive ceramics on the disc surface. The arrangement of weave properties was designed to produce mechanical behavior nearly equivalent to the natural intervertebral disc. Total intervertebral disc replacement at L2-L3 and L4-L5 was performed using 3-DF disc with or without internal fixation in a sheep lumbar spine model. The segmental biomechanics and interface histology were evaluated after surgery at 4 and 6 months.
Results: The tensile-compressive and torsional properties of prototype 3-DF were nearly equivalent to those of human lumbar disc. The lumbar segments replaced with 3-DF disc alone showed a significant decrease of flexion-extension range of motion to 28% of control values as well as partial bony fusion at 6 months. However, the use of temporary fixation provided a nearly physiologic mobility of the spinal segment after implant removal as well as excellent bone-disc fusion at 6 months.
Conclusion: An artificial intervertebral disc using a three-dimensional fabric demonstrated excellent in vitro and in vivo performance in both biomechanics and interface histology. There is a potential for future clinical application.