BioDisc is designed to improve spinal stability, preserve disc height, and reduce recurrent disc herniation.  BioDisc replaces excised nucleus pulposus from the herniated disc, filling the void space with a flexible yet durable protein hydrogel implant that is capable of converting compressive load to tensile load, with the goal of maintaining disc height and range of motion.  The use of BioDisc should have a minimal impact at the point of entry, enhance standard discectomy procedures, and allow patients to return to a lifestyle with less pain and discomfort.

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Normal Spinal Structure and Biomechanics
The vertebral column is the central load bearing structure of the body.  It provides for columnar stability and full six degrees of motion.  The vertebral column achieves the combined stability and motion through the unique structures of the intervertebral disc (IVD).  The annulus fibrosus (AF) consists of multiple fibrillar sheets surrounding a gelatinous core of nucleus pulposus (NP).  The collagen fibers in the annular sheets are oriented circumferentially and at an angular offset, providing great resistance to bursting.  Fibrillar collagen is not well suited to carrying compressive loads, though it has good tensile strength.  Being mostly water, the NP is considered "incompressible", and it freely deforms, though it does not change volume.  Thus under a compressive load, the NP compresses axially and correspondingly expands radially.  When put under tension, the AF constrains the radial expansion of the NP and carries the load circumferentially.

The Problem
A spinal disc herniation, either frank or related to degenerative disc disease (DDD), is one of the common causes of radicular pain (pain radiating down the arm or leg in a specific pattern secondary to nerve root compression).  The conservative approach of physical therapy is sometimes unsuccessful.  If physical therapy does not resolve the pain, surgical discectomy may be necessary.  A discectomy destabilizes the spinal disc and can cause loss of disc height.

This loss of disc height forces the facet joints to carry correspondingly greater loads, ultimately contributing to joint degeneration and further pain.  If the problem remains unresolved, the next step in therapy is either a total disc replacement using an artificial disc or fusion, both of which are major surgical procedures.  Fusion results in restricted motion and can cause damage to the adjacent spinal discs over time.

There are two basic schools of thought on discectomy, with the first taking a minimalistic approach to remove only the "offending fragment" (fragmentectomy) and the second involving a more complete removal of NP from the disc.¹  Neither approach is without problems.  The minimalistic approach, although founded in an understanding of the biomechanical role of the NP, has been suggested to result in somewhat higher rates of recurrent disc herniation, since the defect in the AF does not readily heal.  The more aggressive approach where extensive denucleation is performed may result in a destabilized motion segment; therefore some surgeons may remove less of the NP.  Regardless of the approach, the long-term resolution of back pain is less than satisfactory for many patients.

The Solution
The goal of BioDisc is to enhance the surgical repair of a herniated disc and prevent the destabilization of the motion segment caused by extensive denucleation, as well as reduce the risk of recurrent disc herniation associated with fragmentectomy alone.  BioDisc replaces the removed NP material and fills the void following the discectomy.  Delivered to the denucleated space as a liquid, BioDisc fills the void volume and rapidly forms a semi-solid hydrogel comprised of approximately 63% water by volume.  The physical properties of the hydrogel maintain the conversion of the compressive vertebral load to a tensile loading of the collagen fibers of the AF, while itself being resistant to extrusion.  Additionally, the chemistry of the BioDisc cross-linking process allows for this nucleus replacement to be covalently bound to the surrounding annular tissue.

Removal of the herniation, restoration of the normal spinal biomechanics, and the prevention of recurrent disc herniation are the keys to long-term freedom from back pain.  Accomplishing these goals should also result in the prevention of progressive disc space collapse, facet joint overloading, disc bulging and nerve root compression, all while removing the source of biochemical inflammatory pain generators.

BioDisc is one of the newest possible alternatives to disc herniation treatment.  Unlike fusion and prosthetic IVD devices, BioDisc is designed to offer motion preservation for the patient, while preserving healthy native structures.

Protein Hydrogel Technology
BioDisc Nucleus Pulposus Replacement is a protein-based hydrogel device.  BioDisc is intended to fill the void space within the spinal disc annulus following the removal of the nucleus pulposus (discectomy) in the treatment of lumbar intervertebral disc herniation.  Following a discectomy, the device delivery tip is placed directly into the disc space through the annulotomy and the implant material is easily dispensed into all areas of the nuclear void.  BioDisc is designed to preserve disc height, reduce lumbar motion segment instability, and reduce recurrent disc herniation.

BioDisc NPR is:

• 45% purified bovine albumin
• 10% glutaraldehyde
• combined in the ratio of 4:1
• a flexible, viscoelastic hydrogel implant, and
• proposed to be an adjunct to discectomy to:
• preserve disc height
• reduce lumbar motion segment instability
• reduce recurrent disc herniation

¹ Fountas KN, et. al. Correlation of the Amount of Disc Removed in a Lumbar Microdiscectomy With Lon-term Outcome. Spine 2004; 29(22): 2521-2524.