Front Matter

62 Canine Sports Medicine and Rehabilitation

of cartilage with a dense ECM that is adapted to
resist compressive stress. Fibrocartilage is
found in menisci, the annulus fibrosis of
intervertebral discs, and occurs as a specializa­
tion within some regions of tendon that experi­
ence high compressive loads (Figure  3.15B,C).
Elastic cartilage is a flexible and elastin‐rich car­
tilage found in the larynx, epiglottis, and pinna.
Elastic cartilage is not a significant component
of the musculoskeletal system.
Articular cartilage is a smooth and translu­
cent tissue with high water content (approxi­
mately 70%) and a delicate collagen fibrillar
network. It consists of approximately 50% col­
lagen and 35% proteoglycan on a dry weight
basis. The remaining 10% includes nonstruc­
tural proteins and glycoproteins, along with
various minerals and lipids. Chondrocytes
account for approximately 10% of the volume
of articular cartilage.

The collagen in articular cartilage is predomi­

nantly type II, which forms a complex three‐

dimensional network within the ECM and

accounts for the tensile strength of articular car­

tilage. The massive aggregating PG aggrecan is

the most abundant PG in articular cartilage on

a dry weight basis. The aggrecan core protein

has a molecular mass of approximately 240

kDa. Monomers are rich in chondroitin sulfate

and keratan sulfate side chains and are made

up of approximately 90% carbohydrate. Many

aggrecan monomers may be linked to a sin­

gle  backbone molecule of hyaluronic acid,

generating molecular complexes that may reach

2 × 105 kDa in mass. Articular cartilage also

contains several species of SLRPs, including

decorin, biglycan, and fibromodulin (Roughley,

2006). SLRPs make up a small proportion of

the  proteoglycan mass of articular cartilage;

however, due to their small size, they can be

(A) (B)

(C)

Zone I

Zone II

Zone III

Zone IV

Zone V

Tidemark

Cement line

Figure 3.15 Gross (A) and histological (B) appearance of normal articular cartilage with zonal labeling, and
histological appearance of meniscal fibrocartilage (C).