Page 188 - Textbook of Pathology, 6th Edition

172 external callus is cleared away, compact bone (cortex) is
formed in place of intermediate callus and the bone marrow
cavity develops in internal callus.
COMPLICATIONS OF FRACTURE HEALING. These are
as under:
1. Fibrous union may result instead of osseous union if the
immobilisation of fractured bone is not done. Occasionally,
a false joint may develop at the fracture site (pseudo-
SECTION I
arthrosis).
2. Non-union may result if some soft tissue is interposed
between the fractured ends.
3. Delayed union may occur from causes of delayed wound
healing in general such as infection, inadequate blood supply,
poor nutrition, movement and old age.

Healing of Nervous Tissue
CENTRAL NERVOUS SYSTEM. The nerve cells of the
brain, spinal cord and ganglia once destroyed are not
Figure 6.45 Callus formation in fracture healing. replaced. Axons of CNS also do not show any significant
regeneration. The damaged neuroglial cells, however, may
show proliferation of astrocytes called gliosis.
macrophages clear away the fibrin, red blood cells,
inflammatory exudate and debris. Fragments of necrosed PERIPHERAL NERVOUS SYSTEM. In contrast to the cells
bone are scavenged by macrophages and osteoclasts. of CNS, the peripheral nerves show regeneration, mainly
3. Ingrowth of granulation tissue begins with neovascula- from proliferation of Schwann cells and fibrils from distal
risation and proliferation of mesenchymal cells from end. The process is discussed in Chapter 30. Briefly, it consists
periosteum and endosteum. A soft tissue callus is thus of the following:
formed which joins the ends of fractured bone without much Myelin sheath and axon of the intact distal nerve undergo
strength. Wallerian degeneration up to the next node of Ranvier
General Pathology and Basic Techniques
4. Callus composed of woven bone and cartilage starts towards the proximal end.
within the first few days. The cells of inner layer of the Degenerated debris are cleared away by macrophages.
periosteum have osteogenic potential and lay down collagen Regeneration in the form of sprouting of fibrils takes place
as well as osteoid matrix in the granulation tissue (Fig. 6.45). from the viable end of axon. These fibrils grow along the
track of degenerated nerve so that in about 6-7 weeks, the
The osteoid undergoes calcification and is called woven bone
callus. A much wider zone over the cortex on either side of peripheral stump consists of tube filled with elongated
fractured ends is covered by the woven bone callus and Schwann cells.
united to bridge the gap between the ends, giving spindle- One of the fibrils from the proximal stump enters the old
shaped or fusiform appearance to the union. In poorly neural tube and develops into new functional axon.
immobilised fractures (e.g. fracture ribs), the subperiosteal
osteoblasts may form cartilage at the fracture site. At times, Healing of Muscle
callus is composed of woven bone as well as cartilage, tempo- All three types of muscle fibres have limited capacity to
rarily immobilising the bone ends. regenerate.
This stage is called provisional callus or procallus
formation and is arbitrarily divided into external, intermediate SKELETAL MUSCLE. The regeneration of striated muscle
and internal procallus. is similar to peripheral nerves. On injury, the cut ends of
muscle fibres retract but are held together by stromal
II. OSSEOUS CALLUS FORMATION. The procallus acts connective tissue. The injured site is filled with fibrinous
as scaffolding on which osseous callus composed of lamellar material, polymorphs and macrophages. After clearance of
bone is formed. The woven bone is cleared away by incoming damaged fibres by macrophages, one of the following two
osteoclasts and the calcified cartilage disintegrates. In their types of regeneration of muscle fibres can occur:
place, newly-formed blood vessels and osteoblasts invade, If the muscle sheath is intact, sarcolemmal tubes
laying down osteoid which is calcified and lamellar bone is containing histiocytes appear along the endomysial tube
formed by developing Haversian system concentrically which, in about 3 months time, restores properly oriented
around the blood vessels.
muscle fibres e.g. in Zenker’s degeneration of muscle in
III. REMODELLING. During the formation of lamellar typhoid fever.
bone, osteoblastic laying and osteoclastic removal are taking If the muscle sheath is damaged, it forms a disorganised
place remodelling the united bone ends, which after multinucleate mass and scar composed of fibrovascular
sometime, is indistinguishable from normal bone. The tissue e.g. in Volkmann’s ischaemic contracture.