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Chapter 8
THE INJURY PROCESS
I. The Physics of Sports Injury.
A. The body has many different types of tissues. Connective tissue is the most common
type in the body. Connective tissues include ligaments, retinaculum, joint capsules, bone, cartilage,
fascia, and tendons.
1. In some sports, nearly 50% of injuries are acute and involve either muscle or
tendon tissue.
B. Muscle and fascia are thought to be injured when excessive tension is applied during
contraction, particularly eccentric contractions, which are described as “the simultaneous
processes of muscle contraction and stretch of the muscle tendon unit by an extrinsic force.”
C. Although tendons are strong, strains commonly occur at the distal musculotendinous
junction. Musculotendinous strains are the most common soft tissue sports injury.
II. The Mechanical Forces of Injury. Three types of force can affect connective tissues. These forces
are tensile, compressive, and shear. Although tendons resist tensile forces, they are less effective
against shear and compressive forces. Bone resists compression but is less effective against tension
and shear forces. Ligament, like tendon, resists tensile forces, and is more vulnerable to shear and
compression.
A. Regardless of tissue type, each has a limit to how much force it can withstand (critical
force).
1. The critical force varies for each tissue type and may vary within the same tissue.
Factors such as age, temperature, skeletal maturity, gender, and body weight can affect mechanical
properties of ligaments, for example.
III. The Physiology of Sports Injury
A. The Inflammatory Process. Whenever tissues are damaged, the body reacts quickly with
a predictable sequence of physiologic actions to repair the damage.
1. The body’s initial response to trauma is inflammation, commonly referred to as
swelling. The inflammatory process begins during the first few minutes following the injury.
a. Normal signs and symptoms of inflammation include swelling, pain,
reddening of the skin (erythema), and increased temperature in the affected area.
B. Acute Inflammatory Phase.
1. Trauma results in destruction of millions of cells. Initially, blood flow into the
region is reduced (vasoconstriction), but after a few minutes, increased blood flow (vasodilation)
occurs.
2. Damage to blood vessels results in blood flow into the interstitial spaces, resulting
in hematoma formation. Hematoma is the “localized collection of extravasated blood,” an
important step in the inflammatory process.
3. Decreased blood flow to tissue surrounding the injured area results in blood
clotting, and in some cases, death of healthy cells because of oxygen deprivation (secondary
hypoxic injury). As cells die, they release lysosomes that degrade the cells.
4. Other chemicals are released that affect nearby cells. Substances that cause
changes in nearby blood vessels produce vasodilation and vascular permeability. Chemotactic
substances attract scavenger cells to the area (chemotactic effect).
a. Histamine, a powerful inflammatory chemical, is released from a variety
of cells resulting in short-term vasodilation and increased vascular permeability.
b. Hageman factor (a substance in blood) becomes activated when tissues are
damaged and induces many changes in the damaged area. This factor is responsible for the
production of bradykinin, a powerful inflammatory chemical that increases vascular permeability.
c. The complement system is activated, which plays a role in attracting cells
(chemotaxis) such as leukocytes. This is essential to the inflammatory process.
d. Bradykinin triggers the release of prostaglandins that have a number of
effects within the damaged area including vasodilation, increased vascular permeability, pain, and
blood clotting.
e. As a result of increased vascular permeability, plasma proteins, platelets,
and leukocytes move out of capillaries and into damaged tissue. Leukocytes dispose of damaged
cells and tissue debris by phagocytosis (cell eating).
f. Short-lived neutrophils arrive at the injury site. When they die, they release
chemicals that attract macrophages to the area. Macrophages also use phagocytosis to remove
debris.
g. Arachidonic acid is produced by the action of enzymes supplied by
leukocytes and from phospholipids that were in the membranes of destroyed cells. Arachidonic acid
catalyzes the production of leukotrienes that attract leukocytes to the damaged area.
5. The acute inflammatory phase results in a “walling off” of the damaged area from
the rest of the body and the formation of a mass of cellular debris, enzymes, and chemical
attractants that serves to clean up debris and provide necessary components for tissue repair.
6. The acute inflammatory phase lasts up to 3 to 4 days, unless aggravated by
additional trauma.
C. Resolution (Healing) Phase. This phase involves tissue repair.
1. Specialized types of leukocytes (polymorphs and monocytes) and a type of
macrophage (histocytes) migrate into the area of damage, break down cellular debris, and set the
stage for regeneration and repair.
D. Regeneration and Repair. With the exception of bone, all connective tissues heal by
forming scar tissue that begins to form 3 to 4 days after the injury.
1. Fibroblasts migrate into the damaged area. Fibroblasts are immature, fiberproducing connective tissue cells that can mature into several different cell types.
2. Fibroblasts produce collagen fibers and proteoglycans, large protein molecules
that help retain water in the tissues.
3. The damaged circulatory system begins to repair itself by angiogenesis, the
formation of new capillaries, which interconnect to form new vessels.
4. The healing process can take up to four months and when completed under ideal
conditions, scar tissue can be 95% as strong as the original tissue.
5. Stress is helpful to formation of strong collagen fibers in the new tissue. Thus,
appropriate rehabilitation exercises are critical to this process. Refer to Figure 8.2 on page 104 for
the sequence of steps in the inflammatory process.
6. Bone tissue heals as specialized cells known as osteoclasts migrate into the region
to remove cellular and other debris. Specialized fibroblasts (osteoblasts) migrate into the injured
area from adjacent periosteum and bone.
a. Osteoblasts develop the callus, a zone of collagen and cartilage that is
vascularized. The callus fills in the space between the fractured bone ends. Figure 8.3 on page 105
shows x-rays of a callus in a fractured bone.
VI. Pain and Acute Injury. Pain is often the major concern of the injured athlete, and everyone
copes with pain differently. Pain is as much psychological as it is physiological.
A. As a physiological experience, pain results from sensory input (afferents) received and
transmitted through the nervous system. Pain indicates the location of tissue damage.
1. Sensory information travels on relatively slow nerve fibers called nociceptive C
fibers. Unlike other afferent nerve fibers, they are smaller and not myelinated. Myelination (fatty
covering of nerve fiber) acts as an insulator and enables nerves to transmit information quickly.
2. Messages concerning sensory information that travels quickly to the CNS are
given higher priority than messages that travel more slowly, such as pain.
B. A variety of modalities are used to treat pain. Refer to Table 8.1 on page 105.
C. Athletes with high pain tolerance may underestimate the severity of an injury; athletes
with low tolerance to pain may overestimate the severity. Pain is not a useful indicator of the
severity of an injury. However, coaches should be conservative, and when in doubt, refer the athlete
to medical personnel because pain treatment is not the coach’s domain. Coaches, parents, and
athletes should not treat the pain associated with injury to enable the athletes to return to
participation.
VII. Intervention Procedures. The sports medicine community has not provided a clear set of
criteria for the first aid treatment of acute soft-tissue injury.
A. Suggested treatments for inflammation include cryotherapy, such as applications of
crushed ice packs, commercially available cold packs, and aerosol coolants; ice cups applied by
massage; and immersion in ice water baths.
B. After the acute inflammatory phase has passed, usually 48 to 120 hours following injury,
thermotherapy, the therapeutic use of heat, may be appropriate. This modality includes
commercially available hydrocollator packs, warm moist towels, and ultrasound diathermy.
1. Modalities such as ultrasound should only be used under supervision of trained
allied health personnel, such as an athletic trainer or physical therapist.
C. In addition to cold and heat therapy, pharmacologic agents to prevent swelling (antiinflammatories) or control pain (analgesics) are often used. Most of these drugs are prescribed by
a medical doctor and represent a form of treatment beyond the level of training of coaching
personnel.
1. OTC drugs, such as aspirin, are effective for treating minor acute injuries,
however, coaching personnel should use caution and consult parents when making
recommendations to any athlete under the age of 18.
D. Cryotherapy and Thermotherapy. Changing the temperature of injured tissue can have
dramatic effects on inflammation and healing. In the first few minutes after an injury, direct
application of cold to an acute injury, usually crushed ice, may reduce vasodilation.
1. With extremity injuries, rest, ice, compression, and elevation (RICE) is standard
first aid for sprains, strains, dislocations, contusions, and fractures.
a. Crushed ice placed in a plastic bag is inexpensive and highly effective.
Commercially available chemical cold packs and aerosol sprays are less effective than crushed ice
and can be dangerous.
1. The risk of frostbite from a bag of crushed ice is minimal; human
tissue freezes around 25° F and an ice bag reaches a low of 32° F.
2. Recommended protocol for application of a crushed ice bag is 30
minutes, then removed for 2 hours, and then re-applied for another 30 minutes, if needed.
b. Compression is best achieved by using commercially available elastic
wraps. The wrap also secures the crushed ice bag to the body. Care must be taken to avoid making
the wrap too tight; you should be able to slip two fingers under the wrap after it has been secured.
c. Elevation is self-explanatory but when elevating a lower extremity, support
adjacent joints with padding.
d. Do not risk aggravating injuries by performing tests such as ligament laxity
assessments. Such testing should be performed by trained personnel.
2. Cold application can decrease the recovery time from an injury by reducing cells’
metabolic activity, which lowers their need for oxygen.
a. Cold application also provides an analgesic effect and reduces muscle
spasm.
3. Thermotherapeutic agents such as moist heat packs or ultrasound may have a
beneficial effect on soft-tissue injury. Heat, however, should never be applied during the acute
inflammatory stage because it increases inflammation. Thermotherapies stimulate vasodilation and
are useful during the final stages of injury repair.
E. Pharmacologic Agents. Two groups of pharmacologic agents, steroidal and nonsteroidal
anti-inflammatory drugs (NSAIDs), are available. Both groups interfere with the inflammatory
process and reduce swelling or pain.
1. Steroidal Anti-inflammatory Drugs. Steroidal drugs resemble a group of naturally
occurring chemicals in the body known as glucocorticoids. The exact mechanism of their action in
inflammation is not well understood.
a. Steroids may decrease the amount of chemicals released by lysosomes,
decrease capillary permeability, reduce white blood cell phagocytosis, and reduce local fever. The
best known is cortisone; others include hydrocortisone, prednisone, prednisolone, triamcinolone,
and dexamethasone.
b. Steroids may be taken orally, injected, or introduced through the skin by
phonophoresis or iontophoresis.
c. Steroids must be used with care because they negatively affect collagen
formation, and they can decrease connective tissue strength in the injured region.
2. NSAIDs do not have the negative effects on connective tissues of steroids. These
drugs block the conversion of arachidonic acid to prostaglandin. NSAIDs are popular within the
medical community; reportedly, 1.3 million NSAID prescriptions were written in 1991. Commonly
used NSAIDs are listed in Table 8.2 on page 108.
a. Aspirin has anti-inflammatory, analgesic, and antipyretic effects.
b. Research has been inconclusive regarding the effects of NSAIDs on tissue
healing and strength.
F. The best approach to caring for a soft tissue injury is the application of RICE during the
acute inflammatory phase, followed by a combination of RICE, prescribed medications, and
prescribed and properly supervised rehabilitative exercises.
VIII. The Role of Exercise Rehabilitation. The most effective treatment for many sports injuries is
properly developed and supervised exercise.
A. Rehabilitative exercise has positive effects on collagen formation. Collagen is a major
component of tendon and ligament tissues.
1. According to Knight, exercise increases circulation (which increases oxygen) to
healing tissue and also stresses the tissue, and as a result, “guides” proper structuring of collagen.
2. Collagen formation and tissue regeneration requires 2 to 3 weeks. After the final
phase of healing, the athlete should, when appropriate, have the area properly protected.
B. Rehabilitation programs must be planned by a BOC-certified athletic trainer or a physical
therapist with sports medicine training. Implementation and supervision of the exercise program
usually are the responsibilities of the coach or physical educator.
C. Rehabilitative or therapeutic exercise is a four-phase process consisting of exercise
categories based on a continuum of severity and recovery.
1. In cases of severe injury, reestablishment of ROM is accomplished by having a
therapist move the injured extremity through a series of passive exercises. Passive exercise also
reduces swelling and muscle spasm.
2. During the active assisted phase, the athlete improves ROM and muscle strength
by making an effort to move the injured joint while being assisted by the therapist.
3. During the active exercise phase, the athlete continues to move the joint through
full ROM and uses gravity as resistance to develop strength. The therapist supervises the exercising
athlete.
4. Finally in the resistive phase, external resistance via manual resistance, exercise
machines, or free weights improves the strength of muscles surrounding the injured area to protect it
from future injury.
5. Injury rehabilitation is an ongoing process. Injury-specific exercise should be a
permanent component of the athlete’s total training and conditioning program. See Appendix 7 for
more information about therapeutic exercise programs.
REVIEW QUESTIONS
1. During what type of muscle contraction do the majority of muscle and/or fascia injuries occur?
Answer: It is commonly held that more injuries to muscle and fascia occur during eccentric
contractions.
Page: 100
2. True or False: The proximal musculotendinous junction has been found to be the most common
site for injuries.
Answer: False. Research has demonstrated that, with respect to strains, the distal musculotendous
junction (MTJ) is usually the site of failure.
Page: 100
3. List the three types of mechanical forces that can cause soft-tissue injury.
Answer:
1.) Tensile
2.) Compressive
3.) Shear
Page: 100
4. Define critical force.
Answer: Each tissue has a limit to how much force it can withstand. This limit has been referred to
as the critical force.
Page: 100
5. Describe the major steps that occur during the acute inflammatory phase of an injury, with
particular emphasis on vasoconstriction, vasodilation, and subsequent hematoma formation.
Answer: When tissues such as ligaments, tendons, or bones are damaged due to trauma, millions of
cells are destroyed. Initially, the blood flow to the area is reduced (vasoconstriction); however, after
only a few minutes this is follow by an increased blood flow (vasodilation). The mechanical force
of the injury usually causes damage to a variety of soft tissues, including the blood vessels. As a
result the sudden increase in blood flow into the interstitial spaces results in the formation of a
hematoma.
Page: 101
6. Define chemotaxis.
Answer: The chemotactic effect is when chemicals are released that signal the need for scavenger
cells to migrate to the injured area.
Page: 101
7. Describe briefly the group of chemicals known as prostaglandins and discuss some of their
known physiological effects during the acute phase of an injury.
Answer: Prostaglandins are among the most powerful chemicals in the human body. Prostaglandins
have a number of effects within the damaged area, including vasodilation, increased vascular
permeability, pain, and fever, as well as some related to the clotting mechanism.
Page: 101
8. Briefly describe the overall purpose of the acute inflammatory phase of an injury.
Answer: In essence, the entire acute inflammatory phase results in a walling off of the damaged area
from the rest of the body, along with the formation of a mass of cellular debris, enzymes, and
chemicals that serves to clean up the destroyed structures while also providing the necessary
components for tissue repair.
Page: 102
9. What is the typical duration in hours of the acute inflammatory phase?
Answer: The acute inflammatory phase of an injury lasts up to 72–96 hours.
Page: 102
10. List the types of cells that migrate into the injured area during the early part of the resolution
phase.
Answer:
1.) Polymorphs
2.) Monocytes
3.) Histocytes
Page: 102
11. What type of tissue does not heal itself with scar tissue?
Answer: Bones
Page: 103
12. What are fibroblasts?
Answer: Fibroblasts are immature, fiber-producing cells of connective tissue that can mature into
one of several different cell types.
Page: 102
13. What is angiogenesis?
Answer: Angiogenesis involves the actual formation of new capillaries, which interconnect to form
new vessels.
Page: 103
14. What is the relationship between a bony formation known as a callus and the healing of a
fracture?
Answer: A callus fills the space between the fractured bone ends and can be seen quite clearly on a
standard X-ray photograph.
Page: 103
15. Describe the mechanism for the secondary hypoxic effect as described by Knight.
Answer: The immediate application of ice helps reduce the severity of the secondary hypoxic effect.
Page: 106
16. What is the effect of ice application on the secondary hypoxic effect?
Answer: Application of cold provides an analgesic effect and reduces muscle spasm. These two
effects allow the athlete to engage in therapeutic activities more effectively.
Page: 106
17. True or False: Nerve messages sent to the CNS are ranked based on the number of impulses
received per unit of time.
Answer: True. As different messages are sent to the CNS they are “ranked” based on the number of
impulses received per unit of time.
Page: 103
19. Explain the gate control theory of pain.
Answer: If a pain message and a touch message reach the CNS simultaneously, the touch message
is given higher priority. As a result the CNS first recognizes the touch message, with the pain
message being given a lower priority. The process of rubbing the injured area stimulates the fast
velocity touch receptors, thus blocking the pain signals.
Page: 103
20. Explain briefly the physiological effects of the application of ice, compression, and elevation on
acute inflammation.
Answer: During the first few minutes of the acute inflammatory phase, direct application of cold
may reduce vasodilation, thereby reducing the amount of initial swelling. Additionally, in the case
of an injury to an extremity, rest, ice, compression, and elevation are all extremely helpful and
effective.
Page: 106
21. What is an easy and effective way of applying cold and compression to an injury
simultaneously?
Answer: Compression is best achieved by using a commercially available elastic wrap. It is best to
place the ice bag directly against the skin with the elastic wrap secured over the bag. Wrap in a
closed spiral fashion starting distally and finishing proximally.
Page: 106
22. What is the recommended duration of ice application for the treatment of acute inflammation?
Answer: 30 minutes
Page: 106
23. At what temperature do human tissues freeze?
Answer: 25o F
Page:106
24. At what point during the process of injury repair can thermotherapies be useful?
Answer: After the acute inflammatory phases has passed, usually 48–120 hours following injury,
thermotherapy may be appropriate.
Page: 105
25. Differentiate between steroidal and nonsteroidal anti-inflammatory pharmacological agents.
Answer: Both steroidal and nonsteroidal anti-inflammatory pharmacological agents seem to
interfere with some aspect of the inflammatory process, thereby reducing either the amount of
swelling or pain. Problems with steroidal chemicals involve the negative effects they have on the
process of collagen formation. Nonsteroidal anti-inflammatory drugs do not negatively affect
collagen formation.
Page: 107–108
26. What is the mode of action of NSAIDs with respect to the acute inflammatory phase of an
injury?
Answer: As a group, these drugs appear to block the breakdown of arachidonic acid to
prostaglandin, which in turn decreases the inflammatory response to injury.
Page: 108
27. Give a definition of the acronym OTC.
Answer: Over the counter
Page: 106
28. Give a brief explanation of the four types of therapeutic exercise outlined in the chapter—
passive, active assisted, active, and resistive.
Answer:
1.) Passive: a therapist actually moves the injured extremity through a series of passive exercises.
2.) Active assisted: the athlete becomes a working partner in the exercise process, making a
voluntary effort to move the injured joint while being assisted by a therapist.
3.) Active exercise: the athlete continues moving the joint through a full ROM, using gravity as
resistance in order to stimulate development of muscle strength.
4.) Resistive: external resistance is applied to the joint movements.
Page: 110