Injuries and Healing
HARD TISSUE: INJURIES AND HEALING
Bone is a specialized connective tissue, that provides structural support
for the soft tissues, and act as levers for movement when acted upon by the
various muscles. The ends of most bones form joint surfaces and serve as
attachment sites for ligaments (Reid, 1992, p.103).
Articular cartilage is a tissue that covers the ends of long bones in
synovial joints, whose primary function is to decrease friction and assist
in absorbing shock. It contains no vasculature, acquiring nutrients from
the synovial fluid within the joint, and no nervous structures. Articular
cartilage contains chondrocytes and extracellular matrix, which is composed
of proteoglycans, Type II collagen, and water (Wirth & Rudert, 1996).
Composition of Bone: normal adult bone is comprised of 30 percent organic
material, primarily collagen, and 70 percent mineral, mainly calcium and
phosphate. The organic components of bone give it flexibility and
resiliency, while the inorganic components give bone its hardness and
rigidity (Nordin & Frankel, 1989, p.3).
Bone Physiology: the primary cell responsible for ossification is the
osteoblast, which produces the organic component of bones (Guyton, 1986,
p.941). A small amount of osteoblastic activity occurs continually in all
living bones, on about 4 percent of all bone surfaces at any given time, so
that some new bone is being formed constantly (Guyton, 1986, p.942).
Bone is also continuously being absorbed, which is the function of
osteoclasts. Osteoclasts are large multinucleated cells that are normally
active at any one time on less than 1 percent of the bone surfaces (Guyton,
Bone, like soft tissues, responds to stress, with greater stresses
producing a more dense bone, and a reduction of stress causing bone to be
less dense. This is Wolff’s Law (Reid, 1992, p.103).
Inferences from Wolff’s Law:
The functional unit of bone is the osteon, or haversian system. At the
center of each osteon is a haversian canal, which contains blood vessels
and nerve fibers. The osteon consists of concentric series of layers
(lamellae) of mineralized matrix surrounding the central canal. Along the
boundaries of each layer, or lamellae, are small cavities called lacunae,
which contain a specifically-named osteoblast, called an osteocyte (Reid,
1992, p.105, Nordin & Frankel, 1989, p.4).
Types of Bone
Cortical bone forms the outer shell of the bone.
Cancellous bone within this shell of cortical bone is composed of thin
plates, or trabeculae, in a loose mesh structure. Cancellous bone has a
richer blood supply than cortical bone, thus decreasing healing time when
Cortical bone always surrounds cancellous bone, but the relative quantity
of each type varies among bones and within individual bones according to
Periosteum: the dense fibrous membrane that covers all bones, except for
joint surfaces, which are covered with articular cartilage. Blood vessels
and nerve fibers permeate the outer layer of periosteum. The inner layer of
the periosteum contains osteoblasts, bone cells that are responsible for
generating new bone during growth and repair. The periosteum allows for
bone growth in width (Reid, 1992, p.105).
In the child, the periosteum is thick and loosely attached to the cortex,
allowing for rapid production of new bone.
In the adult the periosteum is thinner and more adherent to the cortex,
producing new bone less readily.
Pathologies of Bone: Osteomalacia, Osteoporosis, and Fractures
- Long Bones
Epiphysis: the expanded bone end that forms a support for the
Epiphyseal plate (or physis): the growth plate, which permits
longitudinal growth, and is located between the epiphysis and the
Metaphysis: the transition area between the bulbous epiphysis and
the shaft of the diaphysis.
Diaphysis: the bone shaft; which forms the major site of
attachment for muscle (Reid, 1992, p.109).
- Short Bones
- Flat Bones
The best way to address osteoporosis, regardless of the type, is to prevent
it as much as possible. The following are major factors that can have a
significant impact on osteoporosis:
- Osteomalacia: "softening of the bones" results from a decrease in
deposition of calcium in the bone, and an increased production of
unmineralized matrix (Aloia, 1989). Bone changes may become very sever,
with the result that the markedly weak and "soft" bones gradually bend and
become progressively deformed (Salter, 1983). Due to the increase in
production of matrix, the bone is more likely to deform rather than
- Osteoporosis: a decrease in qualitatively normal bone, which renders the
individual more susceptible to fractures (Bonnick, 1994). It is associated
with an imbalance between bone resorption and bone formation. Osteoporosis
results when the body has not obtained an adequate amount of mineral from
the environment and when the mechanical load is insufficient for
development of new bone due to physical inactivity (Aloia, 1989).
Type I: "postmenopausal osteoporosis", a decrease in bone mineral
density that develops when circulating estrogen levels decrease,
as is the case in menopause. The prevalence of Type I
osteoporosis is 6:1 between females and males (Edwards, 1994) and
is most prevalent in people between the ages of 55 to 75 (Aloia,
1989). Type I osteoporosis affects primarily trabecular bone.
Type II: "age-related osteoporosis" or senile / involutional
osteoporosis; affects both men and women equally, usually over
the age of 70 in which the loss of cortical and trabecular bone
Hormones: Estrogen is a sex hormone that influences bone growth, including
the ossification of epiphyseal plates (Seely, 1989). After puberty,
estrogen plays a critical role in bone metabolism by regulating the removal
of old bone and the production of new bone. If estrogen replacement therapy
is ongoing after menopause, it can decrease the incidence of fractures
Hormone replacement therapy (HRT) with estrogen has been shown to decrease
the incidence of atherosclerosis, but may increase the incidence of uterine
cancer, breast cancer, and hypertension (Aloia, 1989). Some studies show
that combining estrogen replacement with progestin replacement can decrease
the incidence of uterine cancer (Aloia, 1989.)
Nutrition: Vitamin D and Calcium are important to bone metabolism.
Vitamin D is necessary for normal absorption of calcium into the blood
stream from the intestines. The recommended daily allowance of Vitamin D is
200 units (Bonnick, 1994). Most people acquire an adequate supply of
Vitamin D from the diet and from exposure to sunlight, however this may not
be the case for sedentary persons (Rilin, 1987).
Calcium is the primary mineral composing bone. The skeleton stores 99.5% of
the body’s calcium (Marcus, 1996) and bone supplies plasma with calcium in
time of need. The body’s store of calcium peaks at about 30 to 35 years.
The recommended daily allowance for calcium is 800 mg for adults (Bonnick,
1994.) and 1000 mg for women who are postmenopausal (Heaney, 1991.)
One cup of regular, whole milk contains 291 mg of Calcium.
Exercise/activity: a decrease in activity coincides with a decrease in bone
density (Doye, 1970). When stress is applied to bone, specifically physical
activity, the tissue responds by increasing mass, density, and structural
properties. Although we do not know the exact influence of exercise on bone
mass, most researchers think that it stimulates osteoblast activity and
partially inhibits osteoclast activity. (Kannus, 1996).
One cup of 2% lowfat milk contains 297 mg of Calcium.
One cup of plain yogurt contains 415 mg. of Calcium.
One ounce of american cheese contains 174 mg of Calcium.
Once cup of almonds contains 304 mg of Calcium.
Once cup of broccoli contains 136 mg. of Calcium.
Exercise protocols that include high peak force and strain, short
repetitions and training time, that overload the entire bone, and is
progressive in nature may provide the greatest benefit in bone maintenance
and enhancement (Kerr, Morton, Dick, & Prince, 1996, Vuori, et al., 1994).
It is very important that therapists consider an individual’s bone density
prior to prescribing a specific type of exercise. A person with a low bone
mineral density may acquire fractures from an activity that is exceeds the
strength of the bones (Snow-Harter, et al., 1992).
Weight training: the magnitude of load is more important than the number of
repetitions (Kerr et al., 1996). Weightbearing activities performed 3 - 4
times per week for 45 minutes per session increases bone density in
postmenopausal women (Brown , 1995). The bones that respond to weight
bearing activities will be those that are directly stressed, for instance,
a walking program will slow the rate of bone loss in the legs and spine,
but not in the upper extremities (Krolner, et al., 1983).
Resistance training: limited studies indicate that a progressive weight
training program can increase the bone mineral density in the specific
areas trained (Pruitt et al., 1992.) Resistance training for extremities
using equipment found in fitness gyms performed 2-3 times per week for 20
to 30 minutes increases bone density (Nelson et al., 1991). The training
should emphasize high weights and low repetitions (Marcus et al., 1992).
Smoking and Alcohol consumption: both smoking and excessive intake of
alcohol are positively linked with osteoporosis (Aloia, 1989).
Preventing Osteoporosis: the following is a summary of the preceding
information, also known as "The Ten Commandments of Osteoporosis
- Get enough calcium in a balanced diet.
- Get enough vitamin D in your diet and from sunshine.
- Limit your intake of caffeine, salt, protein, and
- Do not go on starvation diets.
- Exercise regularly.
- Take estrogen (progesterone after menopause if you are at
high risk for osteoporosis).
- Take estrogen if your ovaries have been removed
surgically before menopause.
- Avoid drugs that decrease bone mass.
- Drink alcohol only in moderation.
- Do not smoke.
A fracture is a break in the continuity of a bone due to an applied force.
A fracture always produces some degree of soft tissue injury.
Types of forces:
- Bending (angulatory) Forces: causing transverse or oblique
fractures, with the break usually occurring on the convex side of
- Twisting: produce spiral fractures.
- Traction: a "pulling" force that produces an avulsion fracture, in
which a peace of the bone is pulled away either an attached tendon or
Epiphyseal Plate Fractures: the area of the epiphyseal plate is weaker
than the surrounding bone, ligament, and joint capsule, and is subject
to frequent injury. Because the growth plates are usually ossified by
age 23, the majority of these fractures occur in children. Injury to
the growth plate can lead to growth disturbances, resulting in limb
length discrepancies (Salter, 1983).
- Extent: complete vs. incomplete.
- Configuration: transverse, spiral, oblique, longitudinal.
- Relationship of Fracture Fragments: apposition; rotated,
distracted, impacted, overriding, comminuted, etc.
- Relationship of Fracture to External Environment: open (compound)
versus closed (simple).
complicated: infection, severe soft tissue damage (such as artery,
uncomplicated: minimal soft tissue injury
Fracture Healing: bone is the only tissue in the human body that heals
itself completely with tissue that is ultimately indistinguishable
from the original bone. For this reason, bone healing has been
referred to as bone regeneration, and is basically considered and
exaggeration of the normal remodeling process that occurs throughout
life. Fracture healing occurs in six stages:
Age: because bone growth is more pronounced in children, fracture healing
is more rapid in people under the age of 18-21. Fracture healing is
essentially the same length for people over the age of 21.
- The impact stage: occurs at the moment of injury and lasts until
there is complete dissipation of energy (Reid, 1992, p.113).
- The induction stage: following bony failure, cells possessing
osteogenic potential are stimulated to form bone (Reid, 1992,
p.113). Periosteal and intraoseous osteoblasts around the area of
the break are activated, and large numbers of new osteoblasts are
formed (Guyton, 1986, p.943).
- The inflammation stage: begins shortly after impact and lasts
until the bone ends are united by fibrous union, formed by
increased osteoblast activity producing new organic bone matrix
(occurs during the first and second weeks) (Guyton, 1986, p.943).
- Soft callus stage: occurs when inflammation begins to subside and
the bone ends become "sticky", and are held together by fibrous
tissue and cartilaginous tissue (approximately two to three
weeks). The minerals that comprise the inorganic component of
bone are beginning to be deposited in the fibrous matrix.
Osteoclasts begin to appear in large numbers and absorb portions
of dead bone fragments (Reid, 1992, p.115). Pain is greatly
decreased by this time. The callus is not yet apparent on x-ray.
- Hard callus stage: the callus continues to be "sticky" and is
considered an "osteogenic sleeve" around the fracture fragments.
The callus converts from fibrocartilaginous tissue to fiber bone.
The bone begins to mature as mineralization continues and the
callus begins to be absorbed by osteoclasts. The fracture
fragments are firmly united by bone. The callus is apparent on
x-ray, and the fracture is considered to have undergone clinical
union. (Occurs at approximately three to five weeks) (Reid, 1992,
- Stage of remodeling: occurs when the fracture is healed, and the
diameter of the bone is nearing preinjury size. The callus has
been or is close to being completely reabsorbed. At this point,
the fracture has undergone radiographic union. The fiber bone is
converted to lamellar bone and the medullary canal is
reconstituted. The stage may take a few months to a few years to
be complete (Reid, 1992, pp.113-116).
Site and Configuration: bones surrounded by muscle heal faster than those
surrounded by ligament.
Displacement of Fracture (initially and following reduction): the patency
of the periosteum is critical to healing time: undisplaced fractures heal
twice as fast as displaced fractures. Also, fractures that continue to
experience movement between fragments will heal more slowly, if at all.
Blood Supply to Fracture Fragments: fragments with poor or interrupted
blood supplies will necrose. Areas of bone with a good blood supply (such
as cancellous bone) heals rapidly.
Management of Fractures
Non-intervention: in some cases, physicians will elect not to intervene
when a person has acquired a fracture. This is due to a number of possible
reasons, however in almost every case, the fracture is stable.
Closed Reduction: realignment of fragments externally, using physical
traction, decreases the risk of infection. Casts or splints used to
immobilize fracture site.
Open Reduction Internal Fixation (ORIF): surgical realignment of fracture
fragments, with fragments being held in approximation by hardware such as
plates, screws, pins, nails, intramedullary rods, etc. Bone grafts may also
be used with fractures in which the fragments are not in close proximity to
External Fixation: surgical application of appliances to reduce fractures
externally. Associated with more severe fractures.
Traction: pins inserted in the distal fragment and weights applied to the
fragment, to assist in realignment of the bone. Examples: Buck's traction,
halo traction, etc.
External fixators: use of hardware to hold aligned fragments in place,
usually consists of an external frame to which pins that are drilled
through the various fracture fragments attach. Examples: Hoffman device.
Ilizarov and Debastiani procedures: a specialized external fixator
(consisting of a frame attached to pins that are drilled into fracture
fragments) through which traction can be applied to the bone fragments
(usually larger pieces), to stimulate bone growth. This procedure is used
to lengthen the bone, and is used when significant bone loss has occurred.
Atypical Fracture Healing
Mal-union: bone heals in the normal time frame, but in an unsatisfactory
Delayed union: bone healing takes longer to heal than normal, possibly due
to poor circulation, movement of the fragments, etc.
Non-union: failure of the fracture to heal, resulting in a fibrous union of
the fragments. Possibly due to poor reduction of the fragments, tissue
caught between the fragments, poor circulation, infection, calcium and
phosphorous deficiency, hormonal imbalances, osteoporosis, etc.
Use of cancellous bone grafts: harvested from ilium, etc.
Fracture Healing Complications
Vascular: arterial compromise/tearing; axillary, brachial, and femoral
arteries commonly injured.
Neurological: brain, spinal cord, peripheral nerve damage
Avascular Necrosis: bone ischemia and/or death due to compromised blood
supply; common in the femoral neck, scaphoid, and talus; results in delayed
Joint Stiffness or contracture: occurs primarily when joints are
immobilized via casting, splints, etc.
Myositis Ossificans: due to significant bleeding within muscles; in which
bony spicules are formed within the muscle.
Degenerative Joint Disease: frequently associated with intraarticular
Immobilization Effects: in addition to contracture of joints, also results
in disuse atrophy of muscles, muscle imbalances, altered biomechanics.
Articular cartilage has an incomplete capacity for self-repair. If an
injury is superficial, it may produce a fibrous cartilage matrix, similar
to scar tissue. If the injury is deep, ie, it reaches to subchondral bone,
it may repair by using cells from the bone marrow or from the perichondrium
to fill the defect. In any case, it does not replace the injured cells with
Type II collagen, and thus it loses the original biomechanics of the
injured tissue. Some studies report that fibrous cartilage may over a
period of a year convert to hyaline cartilage, thus restoring the
biomechanical properties of the tissue (Wirth & Rudert, 1996).
Orthopedic surgeons may attempt to stimulate cartilage regeneration by a
number of methods including:
- Drilling into subchondral bone;
- Abrasion of the degenerated cartilage and shaving of the
- Excision of diseased cartilage and subchondral bone;
- Subchondral abrasion with continuious passive motion;
- Osteochondral progenitor cell transplantation;
- Chondrocyte transplantation (Wirth & Rudert, 1996).
Bone heals along similar time frames as does soft tissue. It heals in
a similar fashion as soft tissue, yet with some significant
differences. Bone, much like soft tissues, responds to the stresses
placed upon it by becoming more dense. Current research indicates that
articular cartilage has a limited ability to heal, and if it does so,
the time frame in which it occurs is lengthy.
Therapists become involved with patients who have acquired injuries to
their hard tissues to assist the patient to resume function, to
stimulate tissue healing, or to address some other facet of the
patient’s care. Again, knowledge of how these tissues heal plus an
understanding of the patient’s unique circumstances will guide the
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