Hybrid, combination, and replant materials - Orthopaedic Biomaterials in Research and Practice - page 250

Cartilage
In contrast to bone, articular cartilage has extremely limited capacity
to regenerate itself, largely by chrondrocyte mitosis and replacement;
therefore, relatively minor lesions or injuries to articulating surfaces
of joints may lead to progressive damage and subsequent joint degen-
eration. As described in Chapter 9, cartilage repair using autologous
chondrocyte implantation was first performed in the late 1980s. This
method uses the growth of autologous chondrocytes in a biodegrad-
able matrix, which is then transplanted in place of the damaged tissue.
The basic biological principle behind the use of this technique is that
perichondrial and periosteal tissues contain cells that possess a lifelong
chondrogenic potential. A pool of precursor or adult-type stem cells
is expected to be present in these tissues with self-renewable capacity
and the ability to induce tissue healing. A disadvantage of autologous
chondrocyte implantation is that the donor site may experience severe
morbidity because the explantation site will lose as much chondral
or osteochondral tissue as the diseased implantation site will receive.
Patches from porcine collagen bilayer membranes instead of periosteum
are also being developed as alternative defect fillers. Numerous studies
have shown that repairs achieved with autologous chondrocyte implan-
tation can yield increased type II collagen content, which is “hyaline-
like” cartilage. Thus, the grafted areas tend to show heterogeneity rather
than the typical zones of hyaline cartilage, elastic cartilage, and fibro-
cartilage in natural cartilage. Mesenchymal stem cell transplants also
show promise in inducing bone and connective tissue growth. However,
some concerns with the formation of fibrocartilage and progression of
degenerative changes in the joint have been raised. To overcome this
limitation, further developments have focused on the ex vivo growth of
a three-dimensional cartilage-like tissue, which integrates intimately in
the defect site after being implanted. Other areas of research have also
focused on the use of specific chondrocyte populations rather than an
unselected source of cartilage. This is to provide improved cartilaginous
structure to mimic the distinct phenotypic and functional properties of
chondrocytes across zones of cartilage. A continuing problem has been
the inability to encourage healing between the regenerated and host
cartilage. Cartilage repair and restoration is a relatively new advance-
ment and is becoming an increasingly important part of orthopaedic
care. Knowledge and understanding of the available surgical techniques
are critical to the appropriate use of these interventions.
Carticel (Genzyme Corporation, Cambridge, Massachusetts) is the
first and only FDA-approved cell therapy product used to repair articu-
lar cartilage injuries in the knee of adults who have not responded to
a prior arthroscopic or other surgical repair procedure. The product
was first released as an unregulated device in 1995, largely owing to
the FDA not having a protocol for evaluating human autologous tissue
and cell therapy products. After working closely with the FDA to set
quality standards for cellular products, the FDA approved the product in