Fractures and Their Repair

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There are multiple ways of classifying bone fractures. A stress fracture is a break caused by abnormal trauma to a bone, such as fractures incurred in falls, athletics, and military combat. A pathologic fracture is a break in a bone weakened by some other disease, such as bone cancer or osteoporosis, usually caused by a stress that would not normally fracture a bone. Fractures are also classified according to the direction of the fracture line, whether or not the skin is broken, and whether a bone is merely cracked or broken into separate pieces (table 7.3; fig. 7.17).

The Healing of Fractures

An uncomplicated fracture heals in about 8 to 12 weeks, but complex fractures take longer and all fractures heal

Saladin: Anatomy & I 7. Bone Tissue I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 7 Bone Tissue 235

Table 7.2 Agents Affecting Calcium and Bone Metabolism

Name Effect

Table 7.2 Agents Affecting Calcium and Bone Metabolism

Hormones

Calcitonin

Little effect in adults; promotes mineralization and lowers blood Ca2+ concentration in children; may prevent bone loss in pregnant and lactating women

Calcitriol (vitamin D)

Promotes intestinal absorption of Ca2+ and phosphate; reduces urinary excretion of both; promotes both resorption and mineralization; stimulates osteoclast activity

Cortisol

Inhibits osteoclast activity, but if secreted in excess (Cushing disease) can cause osteoporosis by reducing bone deposition (inhibiting cell division and protein synthesis)

Estrogen

Stimulates osteoblasts and prevents osteoporosis

Growth hormone

Stimulates bone elongation and cartilage proliferation at epiphyseal plate; increases urinary excretion of Ca2+ but also increases intestinal Ca2+ absorption, which compensates for the loss

Insulin

Stimulates bone formation; significant bone loss occurs in untreated diabetes mellitus

Parathyroid hormone

Indirectly activates osteoclasts, which resorb bone and raise blood Ca2+ concentration; inhibits urinary Ca2+ excretion; promotes calcitriol synthesis

Testosterone

Stimulates osteoblasts and promotes protein synthesis, thus promoting epiphyseal growth and closure

Thyroid hormone

Essential to bone growth; enhances effects of growth hormone, but excesses can cause hypercalcemia, increased Ca2+ excretion in urine, and osteoporosis

Growth Factors

At least 12 hormonelike substances produced in bone itself that stimulate neighboring bone cells, promote collagen synthesis, stimulate epiphyseal growth, and produce many other effects

Vitamins

Vitamin A

Promotes glycosaminoglycan (chondroitin sulfate) synthesis

Vitamin C (ascorbic acid)

Promotes collagen cross-linking, bone growth, and fracture repair

Vitamin D

Normally functions as a hormone (see calcitriol)

more slowly in older people. The healing process occurs in the following stages (fig. 7.18):

1. Hematoma formation. A bone fracture also breaks blood vessels of the bone and periosteum, causing bleeding and the formation of a clot (fracture hematoma).

2. Formation of granulation tissue. Granulation tissue is a soft, fibrous tissue produced as a hematoma is infiltrated by blood capillaries and fibroblasts. Macrophages, osteoclasts, and osteogenic cells also invade the tissue from the periosteal and medullary sides of the fracture. Osteogenic cells build up in numbers within 48 hours of the injury.

3. Callus30 formation. Fibroblasts deposit collagen in the granulation tissue, while some osteogenic cells become chondroblasts and produce patches of fibrocartilage called soft callus tissue. Osteogenic cells also differentiate into osteoblasts that produce a bony collar, the hard callus, which they cement to

30 call = hard, tough the dead bone around the injury. This collar acts as a temporary splint to join the broken ends or fragments of the bone to each other. It takes about 4 to 6 weeks for a hard callus to form. During this period, it is important that a broken bone be immobilized by traction or a cast to prevent reinjury.

4. Remodeling. The hard callus persists for 3 to 4 months as osteoclasts dissolve small fragments of broken bone and osteoblasts bridge the gap between the broken ends with spongy bone. This spongy bone is subsequently remodeled into compact bone. Usually the fracture leaves a slight thickening of the bone visible by X ray, but in some cases healing is so complete that no trace of the fracture can be found.

The Treatment of Fractures

Most fractures are set by closed reduction, a procedure in which the bone fragments are manipulated into their normal positions without surgery. Open reduction involves the surgical exposure of the bone and the use of plates,

Saladin: Anatomy & 7. Bone Tissue Text © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

236 Part Two Support and Movement

Open, displaced Greenstick Comminuted Linear

Open, displaced Greenstick Comminuted Linear

Types FracturesBone Fractures And Broken Blood Vessils
Figure 7.17 Some Types of Bone Fractures.

Figure 7.18 The Healing of a Bone Fracture. (a) Blood vessels are broken at the fracture line; blood clots and forms a fracture hematoma. (b) Blood vessels grow into the clot and a soft callus of fibrocartilage forms. (c) Mineral deposition hardens the soft callus and converts it to a hard callus of spongy bone. (d) Osteoclasts remove excess tissue from the hard callus and the bone eventually resembles its original appearance.

Figure 7.18 The Healing of a Bone Fracture. (a) Blood vessels are broken at the fracture line; blood clots and forms a fracture hematoma. (b) Blood vessels grow into the clot and a soft callus of fibrocartilage forms. (c) Mineral deposition hardens the soft callus and converts it to a hard callus of spongy bone. (d) Osteoclasts remove excess tissue from the hard callus and the bone eventually resembles its original appearance.

Saladin: Anatomy & I 7. Bone Tissue I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 7 Bone Tissue 237

Table 7.3 Classification of Fractures

Type

Description

Closed

Skin is not broken (formerly called a simple fracture)

Open

Skin is broken; bone protrudes through skin or wound extends to fractured bone (formerly called a compound fracture)

Complete

Bone is broken into two or more pieces

Incomplete

Partial fracture that extends only partway across bone; pieces remain joined

Greenstick

Bone is bent on one side and has incomplete fracture on opposite side

Hairline

Fine crack in which sections of bone remain aligned; common in skull

Comminuted

Bone is broken into three or more pieces

Displaced

The portions of a fractured bone are out of anatomical alignment

Nondisplaced

The portions of bone are still in correct anatomical alignment

Impacted

One bone fragment is driven into the medullary space or spongy bone of the other

Depressed

Broken portion of bone forms a concavity, as in skull fractures

Linear

Fracture parallel to long axis of bone

Transverse

Fracture perpendicular to long axis of bone

Oblique

Diagonal fracture, between linear and transverse

Spiral

Fracture spirals around axis of long bone, the result of a twisting stress, often produced when an abusive adult roughly picks up a child by the arm

Epiphyseal

Epiphysis is separated from the diaphysis along the epiphyseal plate; seen in juveniles

Avulsion

Body part (such as a finger) is completely severed

Colles31

Fracture of the distal end of the radius and ulna; common in osteoporosis

Pott32

Fracture at the distal end of the tibia, fibula, or both; a common sports injury

31 Abraham Colles (1773-1843), Irish surgeon

32 Sir Percivall Pott (1713-88), British surgeon

31 Abraham Colles (1773-1843), Irish surgeon

32 Sir Percivall Pott (1713-88), British surgeon screws, or pins to realign the fragments (fig. 7.19b). To stabilize the bone during healing, fractures are set in casts. Traction is used to treat fractures of the femur in children. It aids in the alignment of the bone fragments by overriding the force of the strong thigh muscles. Traction is rarely used for elderly patients, however, because the risks from long-term confinement to bed outweigh the benefits. Hip fractures are usually pinned and early ambulation (walking) is encouraged because it promotes blood circulation and healing. Fractures that take longer than 2 months to heal may be treated with electrical stimulation, which accelerates repair by suppressing the effects of parathyroid hormone.

Orthopedics33 is the branch of medicine that deals with the prevention and correction of injuries and disorders of the bones, joints, and muscles. As the word suggests, this field originated as the treatment of skeletal deformities in children, but it is now much more extensive. It includes the design of artificial joints and limbs and the treatment of athletic injuries.

(a)

Figure 7.19 X Rays of Bone Fractures. (a) A displaced fracture of the femur. (b) An ankle fracture involving both the tibia and fibula. This fracture has been set by open reduction, a process of surgically exposing the bone and realigning the fragments with plates and screws.

Children With Osteoporosis Imperfecta

Saladin: Anatomy & 7. Bone Tissue Text © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

238 Part Two Support and Movement

Table 7.4 Bone Diseases

Rickets

Osteomalacia Osteoporosis

Osteitis deformans (Paget35 disease)

Osteomyelitis36 Osteogenesis imperfecta

Osteoma37 Osteochondroma38

Osteosarcoma39 (osteogenic sarcoma) Chondrosarcoma

Disorders described elsewhere Achondroplastic dwarfism 229 Cleft palate 258 Ectopic ossification 230 Fallen arches 284 Fractured clavicle 273

Defective mineralization of bone in children, usually as a result of insufficient sunlight or vitamin D, sometimes due to a dietary deficiency of calcium or phosphate or to liver or kidney diseases that interfere with calcitriol synthesis. Causes bone softening and deformity, especially in the weight-bearing bones of the lower limbs.

Adult form of rickets, most common in poorly nourished women who have had multiple pregnancies. Bones become softened, deformed, and more susceptible to fractures.

Loss of bone mass, especially spongy bone, usually as a result of lack of exercise or a deficiency of estrogen after menopause. It results in increasing brittleness and susceptibility to fractures (see insight 7.4 for details).

Excessive proliferation of osteoclasts and resorption of excess bone, with osteoblasts attempting to compensate by depositing extra bone. This results in rapid, disorderly bone remodeling and weak, deformed bones. Osteitis deformans usually passes unnoticed, but in some cases it causes pain, disfiguration, and fractures. It is most common in males over the age of 50.

Inflammation of osseous tissue and bone marrow as a result of bacterial infection. This disease was often fatal before the discovery of antibiotics and is still very difficult to treat.

A defect in collagen deposition that renders bones exceptionally brittle, resulting in fractures present at birth or occurring with extraordinary frequency during childhood; also causing tooth deformity and hearing loss due to deformity of middle-ear bones.

A benign bone tumor, especially in the flat bones of the skull; may grow into the orbits or sinuses.

A benign tumor of bone and cartilage; often forms bone spurs at the ends of long bones.

The most common and deadly form of bone cancer. It occurs most often in the tibia, femur, and humerus of males between the ages of 10 and 25. In 10% of cases, it metastasizes to the lungs or other organs; if untreated, death occurs within 1 year.

A slow-growing cancer of hyaline cartilage, most common in middle age. It requires surgical removal; chemotherapy is ineffective.

Fractured skull 257 Fractures 234 Herniated disc 265 Joint diseases 320 Kyphosis 263

Lordosis 263 Mastoiditis 254 Osteoporosis 239 Scoliosis 263

35 Sir James Paget (1814—99), English surgeon

36 osteo = bone + myel = marrow + itis = inflammation

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