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7. What is the fluid requirement of a 50-kg man with first-
CHAPTER 8
Burns
degree burns to his left arm and leg, circumferential
second-degree burn to his right arm, and third-degree
burns to his torso and right leg. What is the rate of initial
fluid resuscitation?
A. 4.5 L over 8 hours, followed by 4.5 L over 16 hours
B. 4.5 L over 8 hours, followed by 6 L over 16 hours
C. 6 L over 8 hours, followed by 6 L over 16 hours
D. 6 L over 8 hours, followed by 9 L over 16 hours
Answer: A
The most commonly used formula, the Parkland or Baxter
formula, consists of 3 to 4 mL/kg per % burn of Lactated
Ringer’s, of which half is given during the first 8 hours after
burn and the remaining half is given over the subsequent
16 hours. The most recent American Burn Association consensus formula recommends 2 mL/kg per % burn of Lactated
Ringers given the tendency toward excessive fluid administration with the traditional formulas. The concept behind
continuous fluid requirements is simple. The burn (and/
or inhalation injury) drives an inflammatory response that
leads to capillary leak; as plasma leaks into the extravascular
space, crystalloid administration maintains the intravascular
volume. Therefore, if a patient receives a large fluid bolus in
a prehospital setting or emergency department, the fluid has
likely leaked into the interstitium, and the patient still requires
ongoing burn resuscitation according to the estimates. Continuation of fluid volumes should depend on the time since
injury, urine output, and mean arterial pressure (MAP). As
the capillary leak closes, the patient will require less volume to
maintain these two resuscitation endpoints. Children under
20 kg have the additional requirement that they do not have
sufficient glycogen stores to maintain an adequate glucose
level in response to the inflammatory response. Specific pediatric formulas have been described, but the simplest approach
is to deliver a weight-based maintenance IV fluid with glucose supplementation in addition to the calculated resuscitation with lactated Ringer’s. (See Schwartz 11th ed., p. 254.)
8. A patient with partial- and full-thickness burns to their
torso was intubated emergently and has become increasingly difficult to ventilate demonstrating rising PCO2
and peak inspiratory pressure. The most important treatment includes:
A. Low tidal volume (6 cc/kg) for lung-protection
ventilation.
B. High-frequency percussive ventilation (HFPV).
C. Increase the FIO2 and decrease in positive end-
expiratory pressure (PEEP).
D. Eschar release along the anterior axillary lines with
bilateral subcostal and subclavicular extensions.
9. What is the indication for the topical therapy which can
cause neutropenia when applied to burns?
A. Primarily as prophylaxis against burn wound infec-
tions with a wide range of antimicrobial activity
B. Primarily as antimicrobial prophylaxis against eschar
and newly grafted areas
C. MRSA culture-positive burn wound infections
D. To improve patient comfort while reducing the need
for daily dressing changes
Answer: D
Hypoventilation, increased airway pressures, and hypotension may also characterize thoracic compartment syndrome.
Escharotomies are rarely needed within the first 8 hours following injury and should not be performed unless indicated
because of the terrible aesthetic sequelae. When indicated,
they are usually performed at the bedside, preferably with
electrocautery to minimize blood loss. Extremity incisions
are made on the lateral and medial aspects of the limbs in an
anatomic position and may extend onto thenar and hypothenar eminences of the hand. Digital escharotomies do not usually result in any meaningful salvage of functional tissue and
are not recommended. Inadequate perfusion despite proper
escharotomies may indicate the need for fasciotomy, but this
procedure should not be routinely performed as part of the
eschar release. Thoracic escharotomies should be placed along
the anterior axillary lines with bilateral subcostal and subclavicular extensions. Extension of the anterior axillary incisions
down the lateral abdomen typically will allow adequate release
of abdominal eschar. (See Schwartz 11th ed., p. 259.)
Answer: A
Silver sulfadiazine is one of the most widely used in clinical
practice. Silver sulfadiazine has a wide range of antimicrobial
activity, primarily as prophylaxis against burn wound infections rather than treatment of existing infections. It has the
added benefits of being inexpensive, being easily applied,
and having soothing qualities. It is not significantly absorbed
systemically and thus has minimal metabolic derangements.
Silver sulfadiazine has a reputation for causing neutropenia,
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10. Successful antibiotic penetration of a burn eschar can be
achieved with:
A. Mafenide acetate.
B. Neomycin.
C. Silver nitrate.
D. Silver sulfadiazine.
11. Which of the following is TRUE regarding nutritional
needs of burn patients?
A. The hypermetabolic response to burn wounds typi-
cally raises the basic metabolic rate by 120%.
B. Oxandrolone, an anabolic steroid, can improve lean
body mass but can be associated with hyperglycemia
and clinically significant rise in hepatic transaminitis.
C. Early enteral feeding is safe when burns are <20%
total body surface area (TBSA), otherwise enteral
feeding should await return of bowel function to
avoid feeding a patient with gastric ileus.
D. For patients with <40% TBSA, caloric needs are esti-
mated to be 25 kcal/kg/d plus 40 kcal/%TBSA/d.
but this association is more likely due to neutrophil margination from the inflammatory response following burn injury.
True allergic reactions to the sulfa component of silver sulfadiazine are rare, and at-risk patients can have a small test
patch applied to identify a burning sensation or rash. Silver
sulfadiazine destroys skin grafts and is contraindicated on
burns or donor sites in proximity to newly grafted areas. Also,
silver sulfadiazine may retard epithelial migration in healing
partial-thickness wounds. (See Schwartz 11th ed., p. 257.)
Answer: A
Mafenide acetate, either in cream or solution form, is an
effective topical antimicrobial. It is effective even in the presence of eschar and can be used in both treating and preventing wound infections; the solution formulation is an excellent
antimicrobial for fresh skin grafts. Use of mafenide acetate
may be limited by pain with application to partial-thickness
burns. As mafenide is a carbonic anhydrase inhibitor, a historically described side effect is metabolic acidosis. However,
multiple studies have been performed using mafenide to treat
burn wounds without any significant incidence of metabolic
acidosis. (See Schwartz 11th ed., p. 257.)
Answer: D
Calculating the appropriate caloric needs of the burn patient
can be challenging. A commonly used formula in nonburned
patients is the Harris-Benedict equation, which calculates
caloric needs using factors such as gender, age, height, and
weight. This formula uses an activity factor for specific injuries, and for burns, the basal energy expenditure is multiplied by 2. The Harris-Benedict equation may be inaccurate
in burns of <40% TBSA, and in these patients, the Curreri
formula may be more appropriate. This formula estimates
caloric needs to be 25 kcal/kg/d plus 40 kcal/%TBSA/d. Indirect calorimetry can also be used to calculate resting energy
expenditure, but in burn patients, a “metabolic cart” has not
been documented to be more beneficial than the predictive equations. Titrating caloric needs closely is important
because overfeeding patients will lead to storage of fat instead
of muscle anabolism. (See Schwartz 11th ed., p. 258.)
CHAPTER 8
Burns
12. A 42-year-old man with burns of >40% TBSA was
required a high volume of intravenous fluids over the
first 3 days of his ICU admission to maintain his urine
output, which had finally stabilized. However, he has
become increasingly difficult to ventilate, with high peak
pressures, and his urine output is now declining without response to additional crystalloid. What treatment is
now required for this patient?
A. Discontinuation of crystalloid administration, favor-
ing vasopressor initiation for hemodynamic support,
if required
B. Transitioning from crystalloid to colloid
C. Torso escharotomies
D. Decompressive laparotomy
Answer: D
Massive resuscitation of burned patients may lead to an
abdominal compartment syndrome characterized by increased
airway pressures with hypoventilation and decreased urine
output and hemodynamic compromise. Decompressive laparotomy is the standard of care for refractory abdominal compartment syndrome but carries an especially poor prognosis in
burn patients. Adjunctive measures such as minimizing fluid,
performing torso escharotomies, decreasing tidal volumes,
and chemical paralysis should be initiated before resorting
to decompressive laparotomy. Patients undergoing massive
resuscitation also develop elevated intraocular pressures
and may require lateral canthotomy. (See Schwartz 11th ed.,
p. 258.)
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13. Which of the following statements is FALSE concerning
CHAPTER 8
Burns
surgical treatment of burn wounds?
A. Tangential excision consists of tangential slices of
burn tissue until bleeding tissue is encountered.
Thus, excision can be associated with potentially significant blood loss.
B. Xenographs are a permanent alternative to split
thickness skin grafts when there is insufficient donor
sites.
C. Bleeding from tangential excision can be helped with
injection of epinephrine tumescence solution, pneumatic tourniquets, epinephrine-soaked compresses,
and fibrinogen and thrombin spray sealant.
D. Meshed split-thickness skin grafts allow serosan-
guinous drainage to prevent graft loss and provide a
greater area of wound coverage.
Answer: B
Once the initial resuscitation is complete and the patient is
hemodynamically stable, attention should be turned to excising the burn wound. Burn excision and wound coverage
should ideally start within the first several days, and in larger
burns, serial excisions can be performed as patient condition
allows. Excision is performed with repeated tangential slices
using a Watson or Goulian blade until viable, diffusely bleeding tissue remains. It is appropriate to leave healthy dermis,
which will appear white with punctate areas of bleeding. Excision to fat or fascia may be necessary in deeper burns. The
downside of tangential excision is a high blood loss, though
this may be ameliorated using techniques such as instillation of an epinephrine tumescence solution underneath the
burn. Pneumatic tourniquets are helpful in extremity burns,
and compresses soaked in a dilute epinephrine solution are
necessary adjuncts after excision. A fibrinogen and thrombin
spray sealant (Tisseel Fibrin Sealant; Baxter, Deerfield, IL) also
has beneficial effects on both hemostasis and graft adherence
to the wound bed. The use of these techniques has markedly
decreased the number of blood transfusions given during burn
surgery. For patients with clearly deep burns and concern for
excessive blood loss, fascial excision may be employed. In this
technique, electrocautery is used to excise the burned tissue
and the underlying subcutaneous tissue down to muscle fascia. This technique markedly decreases blood loss but results
in a cosmetically inferior appearance due to the loss of subcutaneous tissue. For excision of burns in difficult anatomic
areas, such as the face, eyelids, or hands, a pressurized water
dissector may offer more precision but is time-consuming,
has a steep learning curve, and is expensive. (See Schwartz
11th ed., p. 259.)
14. Which of the following late complications of an acute
burn has the appropriately described treatment?
A. Hypertrophic burn scars should be excised and
revised to minimize the increasing inflammatory
response.
B. The most common type of contracture is that of the
hand which rarely requires surgical excision.
C. Heterotopic ossification (HO) associated pain can
be often successfully treated with oral pain control,
physiotherapy, and radiation therapy.
D. HO requires surgical excision to prevent malignant
transformation of pathologic lamellar bone.
Answer: C
HO is another long-term morbidity associated with burn
injury. HO is the pathologic development of lamellar bone in
peripheral tissue. Its incidence has been reported to be
between 1% and 3% of burn patients. Symptoms include
decreased range of motion, pain, and swelling overlying
the affected joints. Oftentimes, the pathologic bone formation
can be visualized radiographically with plain X-rays. Risk factors include >30% total body surface area (TBSA), arm burns,
arm grafts, ventilator days, and number of trips to the operating room. Treatment includes aggressive physiotherapy,
nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates, radiation therapy, and rarely surgical excision.
A risk scoring system has been developed to predict which
burn patients are at risk of developing HO based on admission criteria; however, further validation is warranted. (See
Schwartz 11th ed., p. 261.)
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15. Which of the following descriptions of a burn disaster is
TRUE?
A. Do not include exposure to radioactive materials.
B. Should be coordinated by local hospital systems,
regionalization and national plans inappropriately
allocate resources.
C. Thirty percent of patients in mass casualty incidents
suffer from burn injury.
D. Globally, they occur most commonly in the United
States.
Answer: C
Although rare, burn disasters can be devastating to those
involved due to the sudden nature of the event, the difficulty
of managing personnel and resources, a deficit of staff experience in burn management, and relatively small resource
availability for a potentially large number of patients. The
American Burn Association has estimated that up to 30% of
patients in mass casualty incidents suffer from burn injury.
A recent review of the literature between 1990 and 2016 identified 752 burn disasters worldwide, defined as an incident
with ≥50 burn injuries and/or ≥30 burn-related deaths. The
majority occurred in Asia and the Middle East and are thought
to be secondary to rapid industrialization, inadequate fireprevention strategies, and poor building codes. There was a
significant increase in terrorist-related incidences from 2000
to 2015. Finally, the authors demonstrated that international
adoption of the US Health and Human Services guidelines
on bed availability for burns and trauma dramatically underestimated the number of beds needed for burn disasters.
(See Schwartz 11th ed., p. 261.)
CHAPTER 8
Burns
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CHAPTER 9
Phases of healing
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Wound Healing
1. Normal wound healing is divided into phases defined
by characteristic cellular populations and biochemical
interactions. They are:
A. Hemostasis and inflammation, proliferation, matura-
tion, and remodeling.
B. Hemostasis, proliferation and inflammation, matrix
deposition, maturation, and remodeling.
C. Hemostasis and inflammation, platelet aggregation,
maturation and remodeling.
D. Hemostasis, inflammation, remodeling and
maturation.
Inflammation
0246810 12 14 16
Answer: A
Normal wound healing is divided into phases defined by
characteristic cellular populations and biochemical activities: (a) hemostasis and inflammation, (b) proliferation, and
(c) maturation and remodeling. An approximate timeline of
these events is depicted in Fig. 9-1. (See Schwartz 11th ed.,
p. 273.)
Maturation
Proliferation
months
Neutrophils
Macrophages
FIG. 9-1. The cellular, biochemical, and
mechanical phases of wound healing.
Relative number of cells
0246810121416
matrix synthesis
Relative amount of
0246810121416
Days postwounding
Fibroblasts
Lymphocytes
Collagen I
Fibronectin
Collagen III
Wound-breaking
strength
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2. Which of the following is FALSE regarding polymor-
CHAPTER 9
Wound Healing
phonuclear neutrophils (PMNs) and their role in wound
healing?
A. PMNs release proteases that degrade ground sub-
stance within the wound site.
B. Neurophils use fibrin clot generated at the wound as
scaffolding for migration into the wound.
C. Neutrophil migration is stimulated by local prosta-
glandins, complement factors, IL-1, TNFα, GF-β,
platelet factor 4, or bacterial products.
D. PMNs are the first cells to infiltrate the wound, peak-
ing at 24 to 48 hours.
E. Neutrophils release cytokines that later assist with
collagen deposition and epithelial closure.
3. The proliferative phase of wound healing occurs how
long after the injury?
A. 1 day
B. 2 days
C. 7 days
D. 14 days
Answer: E
PMNs are the first infiltrating cells to enter the wound site,
peaking at 24 to 48 hours. Increased vascular permeability,
local prostaglandin release, and the presence of chemotactic
substances such as complement factors, interleukin-1 (IL-1),
tumor necrosis factor-alpha (TNF-α), TGF- β, platelet factor 4,
or bacterial products all stimulate neutrophil migration.
The postulated primary role of neutrophils is phagocytosis
of bacteria and tissue debris. PMNs are also a major source
of cytokines early during inflammation, especially TNF-α,
which may have a significant influence on subsequent angiogenesis and collagen synthesis. PMNs also release proteases
such as collagenases, which participate in matrix and ground
substance degradation in the early phase of wound healing.
Other than their role in limiting infections, these cells do not
appear to play a role in collagen deposition or acquisition of
mechanical wound strength. On the contrary, neutrophil factors have been implicated in delaying the epithelial closure of
wounds. (See Schwartz 11th ed., p. 273.)
Answer: C
Normal wound healing follows a predictable pattern that
can be divided into overlapping phases defined by the cellular populations and biochemical activities: (a) hemostasis
and inflammation, (b) proliferation, and (c) maturation and
remodeling.
The proliferative phase is the second phase of wound healing and roughly spans days 4 through 12. It is during this phase
that tissue continuity is reestablished. Fibroblasts and endothelial cells are the last cell populations to infiltrate the healing wound, and the strongest chemotactic factor for fibroblasts
is platelet-derived growth factor (PDGF). Upon entering the
wound environment, recruited fibroblasts first need to proliferate, and then become activated, to carry out their primary
function of matrix synthesis remodeling. This activation is
mediated mainly by the cytokines and growth factors released
from wound macrophages. (See Schwartz 11th ed., p. 273.)
4. Which of the following is TRUE regarding the fibroplastic phase of wound healing?
A. Early during wound healing, the predominant com-
posititon of the matrix is fibronectin and type II
collagen.
B. After complete replacement of the scar with type
III collagen, the mechanical strength will equal that
of uninjured tissue approximately 6 to 12 months
postinjury.
C. Even though the tensile strength of a wound reaches
a plateau after several weeks, the tensile strength will
increase over another 6 to 12 months due to fibril formation and cross-linking.
D. As the scar matures, matrix metalloproteinases break
down type I collagen and replace it with type III
collagen.
Answer: C
The maturation and remodeling of the scar begins during the
fibroplastic phase, and is characterized by a reorganization of
previously synthesized collagen. Collagen is broken down by
matrix metalloproteinases (MMPs), and the net wound collagen content is the result of a balance between collagenolysis
and collagen synthesis. There is a net shift toward collagen
synthesis and eventually the reestablishment of extracellular
matrix composed of a relatively acellular collagen-rich scar.
Wound strength and mechanical integrity in the fresh
wound are determined by both the quantity and quality of
the newly deposited collagen. The deposition of matrix at the
wound site follows a characteristic pattern: fibronectin and
collagen type III constitute the early matrix scaffolding; glycosaminoglycans and proteoglycans represent the next significant matrix components; and collagen type I is the final
matrix. By several weeks postinjury the amount of collagen
in the wound reaches a plateau, but the tensile strength continues to increase for several more months. Fibril formation
and fibril cross-linking result in decreased collagen solubility, increased strength, and increased resistance to enzymatic
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5. The most common causes of Ehler-Danlos syndrome
are:
A. An acquired collagen deficit.
B. Genetic defects encoding α-chains of collagen type V.
C. Genetic defect in platelet-derived growth factor
(PDGF).
D. Type I and type III collagen genetic defect.
6. Dermal wounds in patients with Ehlers-Danlos syndrome (EDS) should be:
A. Closed in one layer with sutures removed early to
prevent deformity.
B. Closed in two layers, under tension, with sutures
removed after twice as long time.
C. Allowed to heal by secondary intention, as would
commonly fall apart.
D. There is no benefit to external fixation with adhesive
tapes.
degradation of the collagen matrix. Fibrillin, a glycoprotein
secreted by fibroblasts, is essential for the formation of elastic
fibers found in connective tissue. Scar remodeling continues
for many (6 to 12) months postinjury, gradually resulting in a
mature, avascular, and acellular scar. The mechanical strength
of the scar never achieves that of the uninjured tissue. (See
Schwartz 11th ed., p. 275.)
Ehlers-Danlos syndrome (EDS) is a group of 10 disorders
that present as a defect in collagen formation. Over half of the
affected patients manifest genetic defects encoding α-chains
of collagen type V, causing it to be either quantitatively or
structurally defective. (See Schwartz 11th ed., p. 278.)
Answer: B
Closing wounds in patients with EDS might represent a major
challenge to the surgeon. Dermal wounds should be closed in
two layers, approximated with the sutures under tension, and
the stitches should be left in place twice as long as usual. In
addition, external fixation with adhesive tape can help reinforce the scar and prevent stretching. (See Schwartz 11th ed.,
p. 278.)
CHAPTER 9
Wound Healing
7. Patients with Marfan syndrome are associated with what
genetic defect?
A. MFN-1 gene deletion
B. Type I collagen gene mutation
C. COL7A1 gene mutation
D. FBN-1 gene mutation
8. Which of the following is FALSE regarding healing of
full-thickness injuries of the gastrointestinal tract?
A. Serosal healing is essential to form a water-tight bar-
rier to the lumen of the bowel.
B. There is an early decrease in marginal strength due
to an imbalance of greater collagenolysis versus collagen synthesis.
C. Collagen synthesis is done by fibroblast and smooth
muscle cells.
D. The greatest tensile strength of the gastrointestinal
(GI) tract is provided by the serosa.
Answer: D
Patients with Marfan syndrome have tall stature, arachnodactyly, lax ligaments, myopia, scoliosis, pectus excavatum, and
aneurysm of the ascending aorta. Patients who suffer from
this syndrome also are prone to hernias. Surgical repair of a
dissecting aneurysm is difficult, as the soft connective tissue
fails to hold sutures. Skin may be hyperextensible, but shows
no delay in wound healing.
The genetic defect associated with Marfan syndrome is a
mutation in the FBN-1 gene which encodes for fibrillin. Previously, it was thought that structural alteration of the microfibrillar system was responsible for the phenotypic changes
seen with the disease. However, recent research indicates an
intricate relationship that FBN1 gene products play in TGF-β
signaling. (See Schwartz 11th ed., p. 278.)
Answer: D
The submucosa lies radially and circumferentially outside
of these layers, is comprised of abundant collagenous and
elastic fibers, and supports neural and vascular structures.
The submucosa is the layer that imparts the greatest tensile
strength and greatest suture-holding capacity, a characteristic that should be kept in mind during surgical repair of the
GI tract. Additionally, serosal healing is essential for quickly
achieving a watertight seal from the luminal side of the bowel.
The importance of the serosa is underscored by the significantly higher rates of anastomotic failure observed clinically
in segments of bowel that are extraperitoneal and lack serosa
(ie, the esophagus and rectum).
The early integrity of the anastomosis is dependent on
formation of a fibrin seal on the serosal side, which achieves
watertightness, and on the suture-holding capacity of the
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CHAPTER 9
Wound Healing
9. When comparing wound healing of the gastrointestinal
(GI) tract to wound healing of skin, which of the following is TRUE?
A. Wound strength is rapidly recovered in both skin and
GI tract.
B. Collagenase activity is increased throughout the GI
tract after transection and anastomoses.
C. Steroids have a greater impact on wound healing in
GI tract compared to skin.
D. -Penicillamine has no impact on skin wound healing.
intestinal wall, particularly the submucosal layer. There is a
significant decrease in marginal strength during the first week
due to an early and marked collagenolysis. The lysis of collagen is carried out by collagenase derived from neutrophils,
macrophages, and intraluminal bacteria. Collagenase activity
occurs early in the healing process, and during the first 3 to
5 days collagen breakdown far exceeds collagen synthesis. The integrity of the anastomosis represents equilibrium
between collagen lysis, which occurs early, and collagen synthesis, which takes a few days to initiate. Collagen synthesis in
the gastrointestinal tract is carried out by both fibroblasts and
smooth muscle cells. (See Schwartz 11th ed., p. 279.)
Answer: B
(See Table 9-1. Schwartz 11th ed., p. 280.)
TABLE 9-1 Comparison of wound healing in the gastrointestinal tract and skin
GI Tract Skin
Wound environment pH Varies throughout GI tract in accordance with
local exocrine secretions
Microorganisms Aerobic and anaerobic, especially in the colon
and rectum; problematic if they contaminate
the peritoneal cavity
Shear stress Intraluminal bulk transit and peristalsis exert
distracting forces on the anastomosis
Tissue oxygenation Dependent on intact vascular supply and
neocapillary formation
Collagen synthesis Cell type Fibroblasts and smooth muscle cells Fibroblasts
Lathyrogens d-Penicillamine has no effect on collagen
cross-linking
Steroids Contradictory evidence exists concerning
their negative effect on GI healing; increased
abscess in the anastomotic line may play a
significant role
Collagenase activity — Increased presence throughout GI tract after
transection and reanastomosis; during
sepsis, excess enzyme may promote
dehiscence by decreasing suture-holding
capacity of tissue
Wound strength — Rapid recovery to preoperative level. Less rapid than GI tissue
Scar formation Age Definite scarring seen in fetal wound sites Usually heals without scar formation in the
Usually constant except during sepsis or local
infection
Skin commensals rarely cause problems;
infection usually results from exogenous
contamination or hematogenous spread
Skeletal movements may stress the suture
line but pain usually acts as a protective
mechanism preventing excess movement
Circulatory transport of oxygen as well as
diffusion
Significant inhibition of cross-linking with
decreased wound strength
Significant decrease in collagen accumulation
Not as significant a role in cutaneous wounds
fetus
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10. Which of the following is TRUE about bone healing?
A. Erythema and swelling commonly occur as part
of healing, as it occurs as the bone at the fracture site is degraded and normal bone undergoes
revascularization.
B. Erythema and swelling occur during formation of
soft callus.
C. Callus mineralization is complete in 1 week.
D. Erythema, swelling, and pain usually take 5 days to
resolve.
Answer: A
Following any type of injury to bone, several changes take place
at the site of injury to restore structural and functional integrity. Most of the phases of healing resemble those observed in
dermal healing, but some notable individual characteristics
apply to bone injuries. The initial stage of hematoma formation
consists of an accumulation of blood at the fracture site, which
also contains devitalized soft tissue, dead bone, and necrotic
marrow. The next stage accomplishes the liquefaction and degradation of nonviable products at the fracture site. The normal
bone adjacent to the injury site can then undergo revascularization, with new blood vessels growing into the fracture site.
This is similar to the formation of granulation in soft tissue.
The symptoms associated with this stage are characteristic of
inflammation, with clinical evidence of swelling and erythema.
Three to four days following injury, soft tissue forms a
bridge between the fractured bone segments in the next
stage (soft callus stage). The soft tissue is deposited where
neovascularization has taken place and serves as an internal
splint, preventing damage to the newly laid blood vessels and
achieving a fibrocartilaginous union. The soft callus is formed
externally along the bone shaft and internally within the marrow cavity. Clinically, this phase of healing is characterized by
the cessation of pain and inflammatory signs.
The next phase consists of mineralization of the soft callus and conversion to bone (hard callus stage). This may take
up to 2 to 3 months and leads to complete bony union. (See
Schwartz 11th ed., p. 281.)
CHAPTER 9
Wound Healing
11. What type of nerve injury involves disruption of axonal
continuity with preserved Schwann cell basal lamina?
A. Neurapraxia
B. Axonotemesis
C. Neurotmesis
D. Axonolysis
12. Fetal wound healing differs from adults wound healing
in a number of ways. Which is TRUE?
A. Fetal wound healing is slower.
B. All fetal wounds heal without a scar.
C. Fetal wounds continue to be scarless and look like
regeneration throughout gestation until birth.
D. Fetal wounds in late third trimester resemble an adult
wound healing pattern.
Answer: B
There are three types of nerve injuries: neurapraxia (focal
demyelination), axonotmesis (interruption of axonal continuity but preservation of Schwann cell basal lamina), and
neurotmesis (complete transection). Following all types of
injury, the nerve ends progress through a predictable pattern
of changes involving three crucial steps: (1) survival of axonal cell bodies; (2) regeneration of axons that grow across the
transected nerve to reach the distal stump; and (3) migration
and connection of the regenerating nerve ends to the appropriate nerve ends or organ targets.
Phagocytes remove the degenerating axons and myelin
sheath from the distal stump (Wallerian degeneration). Regenerating axonal sprouts extend from the proximal stump and
probe the distal stump and the surrounding tissues. Schwann
cells envelope and help in remyelinating the regenerating
axons. Functional units are formed when the regenerating
axons connect with the appropriate end targets. (See Schwartz
11th ed., p. 281.)
Answer: D
Although early fetal wound healing is characterized by
the absence of scarring and resembles tissue regeneration,
there is a phase of transition during gestational life when
a more adult-like healing pattern emerges. This so-called
“transition wound” occurs at the beginning of the third
trimester, and during this period, there is scarless healing;
however, there is a loss of the ability to regenerate skin appendages. Eventually a classic, adult-patterned healing with scar
formation occurs exclusively, although overall healing continues to be faster than in adults. (See Schwartz 11th ed., p. 282.)
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