Page 847 - Textbook of Pathology, 6th Edition

body’s collagen. Virtually whole of body’s hydroxyproline Hyaline cartilage is the type found in most cartilage-forming 831
and hydroxylysine reside in the bone. The architecture of tumours and in the fracture callus.
bone collagen reflects the rate of its synthesis and may be 2. Fibrocartilage is a hyaline cartilage that contains more
woven or lamellar, as described above. abundant type II collagen fibres. It is found in annulus
BONE FORMATION AND RESORPTION. Bone is not a fibrosus of intervertebral disc, menisci, insertions of joint
static tissue but its formation and resorption are taking place capsules, ligament and tendons. Fibrocartilage may also be
during period of growth as well as in adult life. Bone found in some cartilage-forming tumours and in the fracture
deposition is the result of osteoblasts while bone resorption callus.
is the function of osteoclasts. Bone formation may take place 3. Elastic cartilage is hyaline cartilage that contains abundant
directly from collagen called membranous ossification seen in elastin. Elastic cartilage is found in the pinna of ears,
certain flat bones, or may occur through an intermediate stage epiglottis and arytenoid cartilage of the larynx.
of cartilage termed endochondral ossification found in Diseases of skeletal system include infection (osteo-
metaphysis of long bones. In either case, firstly an uncalcified myelitis), disordered growth and development (skeletal dys-
osteoid matrix is formed by osteoblasts which is then plasias), metabolic and endocrine derangements, and
mineralised in 12-15 days. This delay in mineralisation results tumours and tumour-like conditions.
in formation of about 15 μm thick osteoid seams at
calcification fronts (About > 1 μm of matrix osteoid is formed OSTEOMYELITIS
daily). Uncalcified osteoid appears eosinophilic in H & E
stains and does not stain with von Kossa reaction, while An infection of the bone is termed osteomyelitis (myelo =
mineralised osteoid is basophilic in appearance and stains marrow). A number of systemic infectious diseases may
black with von Kossa reaction (a stain for calcium). Areas of spread to the bone such as enteric fever, actinomycosis,
active bone resorption have scalloped edges of bone surface mycetoma (madura foot), syphilis, tuberculosis and
called Howship’s lacunae and contain multinucleated brucellosis. However, two of the conditions which produce
osteoclasts. In this way, osteoblastic formation and significant pathologic lesions in the bone, namely pyogenic
osteoclastic resorption continue to take place into adult life osteomyelitis and tuberculous osteomyelitis, are described
in a balanced way termed bone modelling. The important role below. CHAPTER 28
of vitamin D , parathyroid hormone and calcitonin in calcium
1
metabolism has already been discussed on page 248. Pyogenic Osteomyelitis

NORMAL STRUCTURE OF CARTILAGE Suppurative osteomyelitis is usually caused by bacterial
infection and rarely by fungi. Pyogenic osteomyelitis by
Unlike bone, the cartilage lacks blood vessels, lymphatics haematogenous route occurs most commonly in the long
and nerves. It may have focal areas of calcification. Carti- bones of infants and young children (5-15 years of age),
lage consists of 2 components: cartilage matrix and particularly in the developing countries of the world. In the
chondrocytes. developed world, however, where institution of antibiotics
Cartilage matrix. Like bone, cartilage too consists of organic is early and prompt, haematogenous spread of infection to
and inorganic material. Inorganic material of cartilage is the bone is uncommon. In such cases, instead, direct The Musculoskeletal System
calcium hydroxyapatite similar to that in bone matrix but extension of infection from the adjacent area, frequently
the organic material of the cartilage is distinct from the bone. involving the jaws and skull, is more common mode of
It consists of very high content of water (80%) and remaining spread. Bacterial osteomyelitis may be a complication at all
20% consists of type II collagen and proteoglycans. High ages in patients with compound fractures, surgical
water content of cartilage matrix is responsible for function procedures involving prosthesis or implants, gangrene of a
of articular cartilage and lubrication. Proteoglycans are limb in diabetics, debilitation and immunosuppression.
macromolecules having proteins complexed with Though any etiologic agent may cause osteomyelitis,
polysaccharides termed glycosaminoglycans. Cartilage Staphylococcus aureus is implicated in a vast majority of cases.
glycosaminoglycans consist of chondroitin sulfate and Less frequently, other organisms such as streptococci,
keratan sulfate, the former being most abundant comprising Escherichia coli, Pseudomonas, Klebsiella and anaerobes are
55-90% of cartilage matrix varying on the age of the cartilage. involved. Mixed infections are common in post-traumatic
cases of osteomyelitis. There may be transient bacteraemia
Chondrocytes. Primitive mesenchymal cells which form bone preceding the development of osteomyelitis so that blood
cells form chondroblasts which give rise to chondrocytes. cultures may be positive.
However, calcified cartilage is removed by the osteoclasts. Clinically, the child with acute haematogenous osteo-
Depending upon location and structural composition, myelitis has painful and tender limb. Fever, malaise and
cartilage is of 3 types: leucocytosis generally accompany the bony lesion. Radio-
1. Hyaline cartilage is the basic cartilaginous tissue logic examination confirms the bony destruction.
comprising articular cartilage of joints, cartilage in the growth Occasionally, osteomyelitis remains undiscovered until
plates of developing bones, costochondral cartilage, cartilage it becomes chronic. Draining sinus tracts may form which
in the trachea, bronchi and larynx and the nasal cartilage. may occasionally be the site for development of squamous
carcinoma. Persistence, neglect and chronicity of osteo-