| Description |
Intervertebral discs (IVDs) are soft tissues between adjacent vertebra, which allow motion of the spine. Unfortunately, the IVD can degenerate with age, disease, and with trauma. To better understand the process of IVD degeneration and the potential for regeneration, researchers have used Ilizarovtype devices to compress and to distract the IVD using a rat-tail model. These devices transmit loads applied to two external rings surrounding the tail, to rods implanted through adjacent vertebra, either compressing or distracting the IVD. However, these devices are typically made of materials that induce artifacts with magnetic resonance imaging (MRI), the standard of human IVD assessment, and provide only gross morphology, but are inadequate to differentiate between the nucleus pulposus and the annulus fibrosus. The goal of this project was to develop an MRI-compatible Ilizarov-type device that allowed observation of nonanesthetized animals during repeated distraction treatments The device developed in this study was constructed of MRI-compatible polysulfone (Psf) rings and carbon fiber rods. By developing new protocols, alignment of the rings and rods were standardized and minimized vascular, neural, and muscular damage to the rat-tail. A custom feedback-controlled pneumatic system inflated a latex bladder inserted between the Psf rings. MRIs were conducted with a loop-gap single-turn solenoid seated in a bed, which accommodated the solenoid's perpendicular orientation to the primary axis of the main magnet and maintained animal homeostasis. In the targeted loading range of 0-10 N, the modulus of the ring/rod constructs implanted into in vitro rat-tails was 5±3 N/mm, but were capable of withstanding up to 32±3 N/mm. Implanting these devices into 49 anesthetized rats resulted in zero intraoperative complications. MRI images provided quantifiable separation of the nucleus pulposus and annulus fibrosus with 30 min scan times. However, two weeks after surgery, the periprosthetic tissues of 38 of the animals became inflamed, requiring treatment with antibiotics and resulted in eight deaths. While the goal of developing an MRI compatible distraction device that allowed observation of nonanesthetized animals during repeated distraction treatments was achieved, replacing the carbon-fiber rods used in this study with a more biocompatible matrix is necessary for future studies. |
