Front Matter

Chapter 3 Musculoskeletal Structure and Physiology 61

During remodeling, the woven bone of the cal­
lus is gradually resorbed and replaced with
denser and more organized lamellar bone, and
the medullary compartment is also reformed.

Cartilage

Cartilage is an avascular connective tissue
composed of chondrocytes suspended in a

specialized ECM containing type II collagen,

elastin, variable amounts of type I collagen, and

a diverse array of proteoglycans. The three

basic forms of cartilage—hyaline, fibrocarti­

lage, and elastic cartilage—differ in composi­

tion and organization of the ECM and are

adapted to specific roles and mechanical envi­

ronments within the body. Hyaline cartilage

forms the contact surface of synovial joints

(Figure 3.15A). Fibrocartilage is a tougher form

Case Study 3.1 Delayed union

Signalment: 7 y.o. M/C Terrier mix. Presented for

evaluation of non‐healing fracture of right radius.

History: Original fracture occurred 4 years prior,

repaired successfully with plate and screw fixa-

tion. Three years later, draining tract appeared on

distal aspect of right antebrachium. Culture yielded

methicillin‐resistant Staphylococcus pseudinter-

medius. Plate removed. Six months later, radius

refractured at original site. Type II external fixator

applied. After  12 weeks of fixation, fracture site

not  healed (Figure  3.14A). Referred for second

opinion.

Examination: Patient bearing minimal weight on

right  forelimb. Disuse atrophy of right forelimb

musculature. Copious drainage from proximal

pin tracts.

Treatment: Fixator removed. Fracture ends debrided

to reopen medullary cavity. Autogenous cancellous

bone graft placed at fracture site. Ring fixator applied

(Figure  3.14B). Postoperatively, intensive rehabilita-

tion designed to promote limb use. Eight weeks

postoperatively, radiographs demonstrated bridging

osteosynthesis at fracture site (Figure 3.14C). Circular

external fixation technique allows axial interfrag-

mentary micromotion, which is highly stimulatory for

mechanosensitive osteoblasts. Successful healing in

this case was attributed to the combined effects of

bone graft, fixation method, and a rehabilitation

program emphasizing rapid return to function.

(A) (B) (C)

Figure 3.14 Delayed union. (A) After 12 weeks of fixation, the fracture site has not healed. (B) An autogenous

cancellous bone graft was placed at the fracture site and a ring fixator applied. (C) Eight weeks postoperatively,

radiographs demonstrated bridging osteosynthesis at the fracture site.