Biomedical Engineering Reference
In-Depth Information
5 Intervertebral Disc Degeneration . . ....................................................... 207
6 Functional Consequences of IDD . . . . . . . . . . . . . . ........................................... 208
7 Nucleus Pulposus Replacement with Polymeric Materials:
A Potential Treatment Option for Symptomatic IDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
8 Tissue Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
8.1 Cell Sourcing for Tissue Engineering of the NP . .................................. 211
8.2 Biopolymeric Scaffolds for Tissue Engineering of the NP . . ...................... 214
9 Animal Models of IDD .................................................................... 223
10 Conclusions . . . . . . . . . . . . .................................................................... 224
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
1
Introduction
Nearly 5.7 million individuals are diagnosed with intervertebral disc (IVD) disorders
annually [
1
]. In the USA alone, approximately 350,000 individuals underwent
surgical procedures in 2005, 75% of which were performed to treat degenerative
changes within the spine, including those changes associated with intervertebral disc
degeneration (IDD) [
2
,
3
]. Some suggest that there are currently between 1.5 and
4 million adults in the USA with disc related low back pain (LBP) [
4
]. Alarmingly,
20% of teenagers have lumbar IVDs that exhibit signs of mild degeneration; these
numbers increase dramatically with age as 10% of all discs in 50-year-olds and 60%
of discs in those over the age of 70 exhibit severe degeneration [
5
].
From a clinician's perspective, patients with severe IDD may present with
debilitating LBP. Although a direct causal relationship between IDD and LBP
has been hard to establish due to the nearly 35-40% of asymptomatic individuals
whom exhibit radiographic evidence of IDD [
6
], there is mounting evidence that
suggests that a relationship does in fact exist [
7
-
10
]. IDD has also been associated
with sciatica and disc herniation, which in the long-term can lead to spinal stenosis,
a major source of LBP and disability [
11
]. This suggests that at least a portion of the
socio-economic impact related to LBP can be attributed to IDD, making it one of
the most expensive healthcare burdens to date. When extrapolating these effects to
a global scale, one quickly comes to appreciate the potential for LBP and IDD to
reach epidemic proportions.
These staggering statistics thus provide the impetus for research into the etiology of
IDD and the development of new treatment strategies, including surgical techniques
and tissue engineering approaches to regeneration of the IVD. As a preamble to
reviewing these strategies, a short description of IVD biology, physiology, pathology,
and current treatment options utilizing polymeric biomaterials is provided.
2 Anatomy of the Intervertebral Disc
The human spine is an exquisite and complex structure from both an anatomical and
functional standpoint. The spine is composed of approximately 24 boney elements,
termed vertebral bodies, which are separated by 23 cartilaginous cushions or “shock
