Extract
The external fixator has been in use for more than a century. The first use
was recorded by Carl Wilhelm Wutzer (1789-1863), who employed pins and an
interconnecting rod-and-clamp system. Parkhill (1897) and Lambotte (1900) used
devices that were unilateral with four pins and a bar-clamp system. By 1960,
Vidal and Hoffmann had popularized the use of an external fixator to treat
open fractures and infected pseudarthroses. The problems encountered with
external fixation in the late twentieth century were predominantly due to a
lack of understanding of the principles of application, the principles of
fracture-healing with external fixation, and the use of old technology. Its
use was reserved for the most severe injuries and for cases complicated by
infection. Thus, pin problems, nonunions, and malunions were common. Since
then, better technology and understanding have allowed for greater versatility
and better outcomes. Simultaneous with developments in the Western world,
Ilizarov developed the principles of external fixation with use of
ring-and-wire fixation. It was not until the late 1980s and early 1990s, when
more interaction and exchange between the West and East (Russia) was possible,
and with the help of Italians who embraced the philosophy of external
fixation, that the use of external fixation was proven to be successful.
Several variations of external fixation have been developed, and its use is
now widespread. Unfortunately, in the United States, all but a minority of
surgeons still have substantial apprehension about the use of external
fixation.
The external fixator has been in use for more than a century. The first use
was recorded by Carl Wilhelm Wutzer (1789-1863), who employed pins and an
interconnecting rod-and-clamp system. Parkhill (1897) and Lambotte (1900) used
devices that were unilateral with four pins and a bar-clamp system. By 1960,
Vidal and Hoffmann had popularized the use of an external fixator to treat
open fractures and infected pseudarthroses. The problems encountered with
external fixation in the late twentieth century were predominantly due to a
lack of understanding of the principles of application, the principles of
fracture-healing with external fixation, and the use of old technology. Its
use was reserved for the most severe injuries and for cases complicated by
infection. Thus, pin problems, nonunions, and malunions were common. Since
then, better technology and understanding have allowed for greater versatility
and better outcomes. Simultaneous with developments in the Western world,
Ilizarov developed the principles of external fixation with use of
ring-and-wire fixation. It was not until the late 1980s and early 1990s, when
more interaction and exchange between the West and East (Russia) was possible,
and with the help of Italians who embraced the philosophy of external
fixation, that the use of external fixation was proven to be successful.
Several variations of external fixation have been developed, and its use is
now widespread. Unfortunately, in the United States, all but a minority of
surgeons still have substantial apprehension about the use of external
fixation.
Look for this and other related articles inInstructional
Course Lectures,Volume 57, which will be published by the
American Academy of Orthopaedic Surgeons in March 2008:• "Fractures of the Hip," by Jeffrey C. Anglen, MD, and
Michael Baumgaertner, MD
Look for this and other related articles inInstructional
Course Lectures,Volume 57, which will be published by the
American Academy of Orthopaedic Surgeons in March 2008:
• "Fractures of the Hip," by Jeffrey C. Anglen, MD, and
Michael Baumgaertner, MD
The goals of this Instructional Course Lecture are to (1) review the
principles of external fixation and describe healing under these conditions;
(2) review existing technology with specific attention to pin design, modular
designs, and aspects of ring fixation for the general practitioner; (3)
outline the paradigm of using the external fixator for bone-healing; (4)
discuss different types of external fixator applications, including
damage-control frames and configurations of hybrid frames for the tibia; and
(5) review pin-care issues and present pin-care techniques that work.
External fixation is a minimally invasive technique whose application and
management have been refined so that it is now another valuable tool in the
management of fractures and other complicated musculoskeletal conditions. From
pin care to frame mechanics, the fixator can be applied and adjusted to meet
the needs in each clinical context, and many of the problems previously
associated with its use can be circumvented. Even so, it is not a panacea and
should not be used in situations in which plates or nails are more suitable.
Currently the external fixator has two common treatment configurations: the
damage-control orthopaedic frame, which was designed to be a temporary device,
and the definitive-treatment frame, which was designed to be used for
definitive management of fractures and for posttraumatic reconstruction. These
two applications are based on different principles of treatment. When the
damage-control frame is used, the impact of the fixator on the systemic state
of the patient and on the definitive intervention that may follow (e.g., plate
or nail fixation) must be considered. Also, it may become necessary to use the
external fixator as the definitive treatment, so it is important to know how
to convert the damagecontrol frame to the definitive-treatmentframe
configuration. When the definitive-treatment-frame configuration is used, it
is critical to understand how to modulate the mechanical properties of the
fixator in response to the bone being treated. Thus, an understanding of how
to "read the bone" is important, as is an understanding of the
techniques of application that allow long-term use of the fixator. Finally,
since some frames will need to be in place for a prolonged period (e.g., those
used for limb-lengthening and salvage), effective management of routine issues
(pin tracks, discomfort, and walking) is necessary.
Damage-Control Frames
The early damage-control frames were used primarily for severe open
fractures because these fractures were not amenable to the fracture fixation
techniques available at the time. Since external fixation was used in the most
extreme cases, it was associated with the most complications, such as
infection and nonunion. Furthermore, effective principles of soft-tissue
management and ways to obtain healing in the presence of exposed bone and bone
loss were just being learned. Nonetheless, for lack of a better option,
external fixation was used. As plate and nail fixation methods improved,
fractures in most polytraumatized patients were stabilized with definitive
fixation immediately (in less than twenty-four to forty-eight hours). This has
been described as the era of early total care. We subsequently learned that,
while early total care was reasonable for the bone, it was not always optimal
for every patient because of numerous systemic issues. The evolution of
collaborative management of the trauma patient, for whom orthopaedic treatment
is carried out within the context of the "big picture," heralded
the modern era of damage-control orthopaedics. In this era, there is
appropriate stabilization of the essential bone injuries (usually with a
damage-control orthopaedic frame), until the patient's systemic condition
becomes optimized, at which point definitive fracture stabilization is
undertaken, usually with nails or plates. While there remains controversy
about the timing of fixation, which is beyond the scope of this lecture, a
definitive indication has been established for external fixation as a method
with which to stabilize the skeleton during the early stages of
polytrauma.
In this lecture, the application of a damage-control orthopaedic frame for
the pelvis and extremities will be described. Simple-to-remember anatomic
windows and simple frame constructs that can be applied to most fractures will
be presented. With the use of battery-powered drills, a single
"damage-control tray" can be assembled to simplify
application.
Definitive-Treatment Frames
When external fixation is used as definitive treatment, it should first be
applied in a configuration that provides the maximum stability (a rigid
construct) to the fresh fracture environment. This is the best environment for
healing of the soft tissues as well as for the early stages of bone-healing.
However, this environment should not be maintained indefinitely because it
will result in excessive stress-shielding of the fracture site and can lead to
an osteopenic nonunion. This type of nonunion is one of the most challenging
to treat since there is not only a problem with healing, but also challenges
with regard to obtaining a stable construct because of the changes in bone
quality. Over time, the external fixator should be changed or modulated to
allow a progressive load transfer or destiffening of the construct to help
stimulate bone-healing.
Once there is evidence of biologic activity (early fracture callus), there
should be a slow and progressive load transfer to the healing callus. As
hypothesized by
Pauwels1 and later
explained in different terms by
Perren2 (with his
interfragmentary strain theory), pure compression and hydrostatic pressure
will stimulate the mesenchymal cells to differentiate toward chondrogenesis
and subsequently endochondral ossification. Strain will result in the
formation of collagenous tissue and subsequent intramembranous ossification.
Combinations of these two temporally spaced events (compression then strain)
can manifest themselves as callus healing or, as is the case with use of the
Ilizarov principle, regenerate
formation2. All of
this, however, depends on adequate blood flow because, in its absence, there
will be no bone-healing, regardless of the type of fracture fixation. Thus, as
the initial construct with the stiff fixator begins to demonstrate some
biologic activity, the fixator undergoes a "controlled
destiffening" so that there is a slow but definitive transfer of
load-bearing from the fixator to the bone. This load-sharing will gradually
stimulate the developing callus until solid bone-healing has occurred.
Several authors have examined both theoretical and practical methods of
analyzing healing in association with the use of external
fixation2-10.
Factors that contribute to the nature and speed of osseous healing include the
location of the fracture, the nature of the blood supply, and the method of
fixation (pin or wire configuration). While the experience has not been well
documented in the English-language literature, those who have visited the
center in Russia established by Ilizarov have seen remarkable work, all done
with fine wire fixation. Metaphyseal healing within three to four weeks,
massive reconstructions, and eradication of infection have all been
demonstrated (personal communication). Again, as a result of the historic
geopolitical issues, such information has not been well disseminated in the
Western literature. What the Russians have demonstrated clearly is that
appropriate concern regarding the biology of the soft tissues as well
as that of the bone, along with stable frame configurations and
physiologic loading, can result in reliable healing with use of external
fixation. Usually, frame constructs start out stiff and progressively transfer
load to healing bone.
However, two crucial elements are not well known: how to optimize the load
transfer (destiffening) and how to know when it is complete and the fracture
has healed. Still, the goal of external fixation is to provide what has been
called flexible stability. The stability is provided by the frame and
the construct while the flexibility is added by manipulating the components.
Incidentally, this is the same principle on which modern plate-fixation
techniques are based. As constructs began to include longer plate spans with
fewer screws, the introduction of locked plates essentially resulted in an
internalized fixator. Now it is commonplace to use longer plate spans with a
few widely spaced locked screws to obtain a flexible (long-span) but stable
(locked-screw) construct.
The ring fixator is based on the same principles, in that initial stability
is achieved with multidirectional wires or pins and little initial
weight-bearing is allowed to obtain a stable environment. Then, as
weight-bearing is initiated, there is a controlled axial micromotion that
provides the stimulus for fracture-healing. Since the device is inherently
flexible and yet stable, it achieves the same end result. In fact, as
tensioned wires are loaded, they often loosen and serendipitously transfer
more load to the construct. If this occurs too quickly, the subsequent
excessive instability will result in pin-related problems and discomfort;
hence, the saying among experienced users of ring-and-wire fixators has been:
"A stable frame is a comfortable frame, and a comfortable frame is a
stable frame."
Because use of ring and wire fixators is complex, in this lecture, we will
only discuss the use of the simpler hybrid frame. With use of this frame, the
principles that should be followed include beginning with a rigid frame
construct. As the construct with the stiff fixator begins to demonstrate some
biologic activity (fracture callus equals evidence of vascularity), the
fixator undergoes a "controlled destiffening," so that there is a
slow but definitive transfer of load from the fixator to the bone during
weight-bearing activities. In theory, this load-sharing gradually stimulates
the developing callus until healing has occurred. If there is no evidence of
biologic activity or vascularity (i.e., no callus), an intervention such as
bone-grafting or resection and transport should be considered. An atrophic
nonunion will not heal regardless of the device that is used.
There are many different pin designs, and there remains a philosophical
rift among surgeons with regard to the best way to place pins. What we have
learned is that mechanical chipping and thermal necrosis of the bone are
deleterious to pin longevity and that the most important factor may be the
management of the soft tissues around the pin. Older pins were designed either
to be placed after predrilling or to be self-drilling and threading. There are
pros and cons to both methods. With predrilling, the cutting should be done
with sharp, well-designed drills, and the thermal necrosis and mechanical
issues are minimized. (It is important for the surgeon to check the drills to
ensure a sharp bit.) However, there is definitely a wobble during the
subsequent hand placement of the pins. This wobble can result in a small but
meaningful conical deformation of the near cortex, which reduces the initial
stability of the pin in the near cortex and increases the stress in the far
cortex. On the other hand, the older spade-tipped pin (also called a
trocar), which was drilled directly into the bone, resulted in
chipping of the bone and sufficient heat generation to cause necrosis of the
bone. Thus, their poor design defeated their advantage (except in metaphyseal
bone).
Subsequently, pin designs have included a modified drill point with flutes
along with threads with a cutting lead edge for tapping, followed by threads
for fixation. This allows one-step placement of pins that minimizes thermal
and mechanical complications. The pins can be placed with a motorized device,
and the controlled axial motion of insertion minimizes the wobble of hand
placement. Critics of one-step insertion point to the difficulty in feeling
the far cortex as well as the theoretical possibility of stripping the
near-cortex threads when the cutting tip encounters the endosteal surface of
the far cortex. However, the use of appropriate cutting tips as well as an
appropriately designed thread pitch allows the advancement speed of the pin
(determined by the thread pitch) to be controlled such that the pin engages
and cuts through the far cortex without problems. Furthermore, as a result of
the brief resistance of the pin tip as it encounters the far cortex, there is
usually an audible and palpable drain on the drill motor at such an instant.
This alerts the surgeon that the far cortex has been reached so that
over-penetration can be avoided.
Such theoretical advantages were demonstrated in a study of dogs by Seitz
et al., who found a 22% decrease in the pull-out strength of self-drilling
pins placed with motorized power as well as a substantial wobble with pins
placed by hand11.
Since pull-out is rarely a mode of failure and loose pins are a frequent cause
of pin and/or soft-tissue problems, the potential downside of wobble makes
power insertion an attractive option. The downside of power insertion is
mainly related to the use of improper technique.
The issue of heat generation with self-drilling pins was studied with
thermocouples used near each cortex and measurement of heat generation during
several modes of pin insertion and was determined to depend on numerous
factors12. In that
study, comparison of predrilling with hand insertion, hand insertion of
self-cutting pins, and power insertion revealed no apparent differences among
the three methods of insertion. In fact, power insertion appeared to generate
less heat. The obvious question is why would the placement of self-cutting,
self-tapping pins with power generate less heat than the other methods? The
most likely conclusion would be that the time in contact with bone causes
frictional heat during insertion. Thus, although power insertion appears more
aggressive, because it involves less time of frictional contact with the bone
it theoretically creates less heat. Modern self-drilling pins placed with
power have been in use clinically for many years and have demonstrated good
performance. One compromise is to predrill the holes with a sharp drill and
use power to place the pins to avoid the wobble that can occur with manual
placement.
Since the late 1990s, we have used battery-powered drills to place
self-drilling, self-tapping half-pins (thus, there has been no hand insertion
or predrilling), but we have paid diligent attention to soft-tissue care. It
is important to feel and listen to the pins during insertion. Usually, there
is a brief delay as the drill point cuts through the near cortex, after which
it steadily progresses. Then there is a slight sensation of resistance and a
change in the drill-motor pitch when the far cortex is reached. The advance
should be stopped at that point. If resistance is encountered and excessive
drilling is required, something is wrong and the pin may need to be
repositioned.
Another recent advance has been the use of pin coatings both to enhance
fixation and to reduce infection. Silvercoated pins have been shown to be
associated with less bacterial colonization than uncoated pins, but their
clinical performance has not been found to be definitively superior to that of
uncoated pins. There is also a potential for systemic silver absorption with
their use13.
Hydroxyapatite-coated pins have had an excellent track record with regard to
fixation and longevity and have outper-formed standard titanium pins with
regard to both infection and
longevity14.
Finally, tapered pins were developed to increase radial preload and insertion
torque, both of which have been found to improve pin longevity. However, if
the pins are backed up, even a slight amount, their benefit is lost because of
the taper, and they need to be well monitored. As a result of these issues as
well as the successful performance of other designs, the practical value of
tapered pins is questionable at this juncture.
There are various designs of external fixators. Outdated, single-bar
devices had difficulty in maintaining fracture alignment. The improved
manufacturing and design of clamps (such as those made by Stryker, Synthes, or
Smith and Nephew) have led to newer modular designs that are very
user-friendly and adaptable to a wide variety of clinical scenarios. The
modern so-called unilateral alternatives, such as those with multidirectional
connections and clustered pin clamps on each side (EBI and Orthofix types),
have had an equal amount of success when used properly and have even been
expanded to be more modular. We are not aware of any study demonstrating
clinical superiority of any one design. We prefer modular designs because they
are light, are easy to apply, and provide the maximal versatility in most
clinical situations. Their application will be outlined below.
The circular fixator has a long history and was popularized by those who
followed Ilizarov's philosophy. Because of a long learning curve, maintenance
problems, and other difficulties, this device was accepted by only a minority
of orthopaedic surgeons. In response, the hybrid frame was developed to
provide some of the advantages of the ring design with the ease of application
of standard fixators, particularly for periarticular fractures. The hybrid
frame was initially popular and then quickly went out of favor because of high
rates of complications and failures. If the literature is critically reviewed,
it is apparent that most of the failures of ring fixators, both Ilizarov and
hybrid devices, occurred in the treatment of more severe injuries. Use of such
methods to treat severely disrupted soft tissues and highly comminuted
articular segments was doomed to fail and, in short, the application of these
frame designs was pushed beyond their abilities. Thus, it was less the fixator
and more the indication or application that was at fault. If applied for the
proper indication, hybrid frame designs can work
well15.
Furthermore, application of these fixators is not like insertion of a plate or
nail (passive management) since it requires active (but simple) management.
The recommended application and management of a hybrid frame
(Fig. 1) will be outlined
later.
A new issue that has arisen is the safety of external fixator parts during
magnetic resonance imaging of either the limb or other body parts.
Magnetic resonance imaging-safe means that a fixator does not
generate any deleterious effects (no known hazards) in any magnetic resonance
environment. Magnetic resonance imaging-conditional means that the
individual parts do not generate any deleterious effects in specifically
defined (e.g., 1.5-T) magnetic resonance environments. There are three issues
related to safety during magnetic resonance imaging:
1. The magnetic field causes a diret force on magnetic materials. It is not
a problem with nonmagnetic steel, aluminum, carbon, or plastic.
2. Induced electric currents can be produced in a magnetic field. Most
modern fixator components are not individually magnetic, but when the
components are linked together, as in a standard fixator frame, a closed
circuit is created and an electric current can be induced by the magnetic
field. This is true even when carbon fiber or other non-metallic material is
used because virtually all elements have some degree of conductivity and
inductivity. A circuit of magnetic resonance imaging components with carbon
rods and a loop into the patient can generate clinically relevant
currents16,17.
3. Heating of materials can occur. The induced current can cause heating of
the device and perhaps local tissue damage. There is little to no clinical
data regarding this phenomenon, and the United States Food and Drug
Administration is yet to rule on what is considered "safe."
Currently, there is no industry standard for what is considered magnetic
resonance imaging-safe or what is clinically safe. Only one company to date
has attempted to "insulate" the construct against any inductive
currents, but there is still a known temperature gradient that forms.
The resultant interaction of the frame with the machine itself can disturb
the calibration of the magnetic resonance machine, which can be damaging and
costly to repair. Finally, even when it is possible to perform magnetic
resonance imaging on a patient with an external fixator, clamps located near
the field being scanned, even when several centimeters from the skin, can
result in enough interference to make the scan meaningless. We recommend
judicious use of magnetic resonance imaging, with the fixator clamps placed as
remote from the area of interest as
possible18. In
addition, it should be remembered that magnetic resonance imaging safety with
regard to the individual components of the fixator does not ensure safety of
the magnetic resonance imaging when the frame is assembled into a closed
circuit, and one should beware of misleading marketing claims in this
regard.
The external fixator is an ideal device with which to obtain healing
because it is one of the only devices that provides a stable construct in
which the mechanical parameters (rigidity and alignment) can be modulated as
needed throughout treatment. The frame is usually applied to create as much
stability as possible at the fracture site. Later, with minimal adjustments,
the system can be made more flexible to allow micromotion or macromotion to
help stimulate healing of the fracture. Furthermore, if problems develop with
parts other than the pins or wires, those parts are easily replaced. With
modern designs, there have been very few reported failures or broken parts,
although exceptions do occur with some of the ball-cam designs. In these
designs, a ball is eccentrically turned to lock an interference fit into
place, but if there is even minimal loosening the entire mechanism may
suddenly release; therefore, we prefer locking mechanisms other than the
ball-cam design.
The technique for definitive fixation is based on the concept of the stable
base as taught by James Hutson, MD (personal communication). With this method,
each fixation segment has a stable configuration of pins or wires and an
external fixation module (ring, clamp, or bar). Then individual stable bases
are connected to each other in the desired orientation. Frequently, a common
bar or clamp can be used for more than one segment (transport frames), but
ensuring that each independent segment has a stable configuration is
important. Our preference is to place at least three or four fixation wires or
half-pins (for a metaphyseal segment) or three half-pins (for a diaphyseal
segment) so that one or two can be removed if necessary without destabilizing
the construct. In the event that the fracture does not heal or another problem
requires removal, the frame should be removed and the fracture should be
controlled with external bracing for one to two weeks prior to internal
fixation. The infection rate associated with intramedullary nailing after
external fixation is relatively low (8%) in the absence of a true pin-track
infection, but most traumatologists recommend an interval of frame removal,
pin-track curettage, and perhaps antibiotic coverage prior to placement of the
intramedullary nail. We recommend drilling and curettage of the pin tracks to
remove any colonized or necrotic tissue that could increase the risk of
infection. We also treat the patient with a broad-spectrum antibiotic for one
or two weeks before placing the internal fixation. Although there is little
evidence on which to base this recommendation, we believe that the morbidity
and costs of a subsequent infection justify the use of such a
protocol19.
There have been several studies in which the different healing patterns of
fractures have been measured while the extremity was in an external
fixator3-6.
In these studies, the stiffness and strain of the fracture callus were
measured during the healing process and the authors outlined how healing
occurs. The common finding of these studies is that, if the fracture is to
heal, a proper load transfer from the external fixator to the developing
callus is necessary. As noted previously, the first stage of application of
the external fixation should achieve a rigid construct to allow the earliest
stages of the fracture-healing process to begin as well as to allow the soft
tissues to recover. Once there is early callus formation, the frame needs to
be progressively "destiffened" to transfer more and more load to
the developing callus. If the construct is made too flexible too early, the
resultant strain may exceed the local limits of the developing callus and
produce a nonunion. In contrast, if there is insufficient load transfer, there
will be inadequate callus formation, bone resorption, and disuse osteopenia.
Both of these situations are undesirable. Removing bars, adjusting the
locations of bars, or removing pin and/or wire components can destiffen the
construct in a systematic way to achieve fracture-healing.
With use of ring designs, the load transfer is usually a repetitive
stimulus that occurs with increased physiologic loading. As healing
progresses, wires and half-pins can be removed or support struts can be
loosened. Finally, intervening struts can be removed altogether, and the
patient can have a trial of weight-bearing. This is done so that, if pain
occurs with weight-bearing, the struts can be reapplied with the pre-sumption
that healing is incomplete and a repeat trip to the operating room to reapply
removed "stable bases" is not required.
If a modular or monolateral design is used in the tibia, the key element is
the anteromedial stabilizer since the center of gravity is medial during
singlelimb stance. Having main fixator struts or bars near the center of
gravity minimizes the cantilever load on the fixator pins. With a true
monolateral system, the frame is placed in the anteromedial quadrant of the
leg, and, as healing progresses, the fixator is either manually compressed or
progressively dynamized. In modular hybrid constructs, there is an
anteromedial strut and a secondary bar that connects to the lateral side of
the leg and creates a triangular or delta-shaped construct. In these
configurations, the delta bars are the first to be removed. This is followed
by moving the anteromedial bar farther from the skin or by reducing the number
of pins and/or wires in each segment. While there are several methods
available to decrease stiffness and allow load transfer to the healing callus,
these actions are done only when there is ample radiographic and clinical
evidence of healing (callus progression and pain-free function). Before
complete dynamization occurs, a trial of disconnection with weight-bearing
(usually in the physician's office or for one week) is carried out to ensure
that clinical healing is occurring (Fig.
2).
These are the simplest of frames, and many configurations are possible. The
ones described here allow percutaneous placement (away from vital structures)
while providing adequate initial stability and wound access and minimizing the
risks associated with delayed internal fixation.
Humerus: Five-millimeter pins should be placed in the
anterolateral quadrant of the proximal part of the humerus and in the
posterolateral quadrant of the distal part of the humerus. Fine wires and 4-mm
pins can be used in very distal fragments (Figs.
3-A, 3-B, and
3-C).
Forearm: In most of the forearm, the subcutaneous border of the
ulna can be used as a suitable landmark, but only 3-mm (distal) or 4-mm
(proximal) pins should be employed. The radius is not as suitable for
percutaneous fixation, and an open approach is recommended if such fixation is
used.
Pelvis: The anterior superior iliac spine is an excellent
landmark, and 5-mm pins should be directed medially and posteriorly. If the
fixator is to be used to reduce an "open-book" type of pelvic
fracture (e.g., internal rotation of the hemipelvic segments), the pin should
not exit the iliac wing laterally because, with manipulation of the displaced
pelvic fracture, the pins can just rotate in the iliac crest, leaving the
fracture unreduced. Also, such pins will become loose and contribute to skin
problems. In these cases, it is preferable to err with the pin exiting the
inner table so that, during the reduction maneuver, pin rotation is resisted
by the inner table of the ilium (Fig.
4). Conversely, if the fixator will be used to "open"
the pelvis, as in the treatment of a lateral compression injury, pin placement
should err to the outer cortex for similar mechanical and soft-tissue reasons.
If needed, a superior acetabular pin can be placed 5 to 10 cm proximal to the
tip of the greater trochanter in line with the femur to provide fixation. Care
should be taken that this pin does not penetrate into the soft tissues of the
pelvis. Alternatively, through an open approach, the anterior inferior iliac
spine can be used for pin placement with the pin directed posteriorly. We
recommend against placing pins in the greater trochanter because of the high
risk of infection.
Femur: Along the entire length of the femur, the anterolateral
quadrant is best suited for placement of 5-mm pins. The anterolateral aspect
of the thigh contains no vital structures, and the pin tracks do not interfere
with subsequent surgical approaches (Figs.
5-A and 5-B).
Tibia: The anteromedial quadrant is best suited for 5-mm pins, as
there is little soft tissue and easy access. We place the pins perpendicular
to the anteromedial face of the tibial cortex
(Fig. 6).
Knee: The knee can be stabilized with placement of pins into the
anteromedial aspect of the tibia and the anterolateral aspect of the femur to
create a stable base in each segment. A single large bar should be connected
to each pin pair with adequate length to connect to another bar. An
intercalary bar completes the zigzag or z construct
(Fig. 7).
Ankle: The ankle can be stabilized with use of a single 4 or 5-mm
transfixion pin across the calcaneus, with or without the addition of 4-mm
midfoot or metatarsal pins. Because of problems with loosening of transfixion
pins in the calcaneus, we now prefer to use two posterior calcaneal pins
attached to a u-shaped bar or ring. These pins seem to create fewer problems.
We would caution against placing two transverse pins into the calcaneus
because of the risk of damage to vital structures on the medial side, such as
the flexor tendons and the neurovascular
bundle20,21
(Fig. 8).
When building an external fixation frame, one should first create a stable
base in each bone segment. To achieve this, a single bar is placed between the
two pins in each fragment. Then another bar (an intercalary bar) is connected
to the bars in each base. For example, when two pins are placed into the
femoral fragments, there should be a bar that connects the two pins in each
fragment, and then an additional bar is used to stabilize the fracture. If the
intercalary bar is connected to only one of the two pins in each base, the
resultant stability of the construct may be inadequate because the holding
power and the stability of a bar-to-bar connection is greater than that of a
bar-to-pin connection. Another strong recommendation is to place the
compartment, through which a pin is passing, on stretch during insertion. For
example, if a wire is passing across the distal part of the femur from
posterior-lateral to anterior-medial, the knee is straightened (to place the
posterior muscletendon units on stretch) during initial insertion; then, as
the pin exits anteromedially, the knee is flexed (to place the medial
quadriceps muscle-tendon units on stretch). This maneuver not only helps
maintain motion around the adjacent joint but also minimizes irritation by the
pin during such motion. This can help minimize irritation of the tissues and
facilitate pin care.
The application of a hybrid frame to either the proximal or the distal part
of the tibia is relatively simple (Figs.
9-A and 9-B). The hybrid frame
is best used for extra-articular or very simple fractures (C1 according to the
AO/OTA classification system). Originally, one would use two or three wires
and/or one or two half-pins in the articular segment with a longitudinally
parallel support member in the anteromedial quadrant of the leg and a delta
support bar. As soft tissues stabilize and weight-bearing is initiated, the
surgeon monitors the radiographs for evidence of healing. If callus is present
(at approximately two to four weeks), load transfer is initiated by one of
several methods. Having the patient bear weight statically while the delta bar
is loosened and then retightened resets the load on the bar and effectively
transfers some load to the bone. Removal of a wire or pin will also destiffen
the construct, but we recommend against this method in case any problems
develop with the remaining pins. If a dynamic component has been used, it can
be dynamized as described below. In the absence of a dynamic component,
another, more practical method is to move the bar farther from the skin
(bone), which would effectively decrease the stiffness of the frame and result
in greater load transfer at the site of callus.
Progressive weight-bearing increases load transfer. When a dynamic device
is used, as is our preference, load transfer can be started by dialing 1 mm of
axial motion into the system. As healing progresses (i.e., at approximately
six weeks), more load is transferred by increasing weight-bearing further and
by removing the delta bar. With dynamic components, more motion can be dialed
in. This process is continued so that, by twelve weeks, some half-pins can be
removed and/or more motion can be dialed in. At sixteen weeks, if the
radiographs and clinical status warrant it, the components are disengaged
while the metaphyseal and diaphyseal stable bases are maintained. This allows
full load transfer while keeping the frame components in the leg but not
connected in case healing is incomplete and more time in the fixator is
required. The remainder of the device is removed one week later if the patient
has no symptoms and the fracture remains aligned. With use of this algorithm,
if there is satisfactory initial reduction, progressive physiologic loading,
and progressive dynamization (load transfer), fracture-healing can frequently
be expected. In our experience with a series of proximal and distal tibial
fractures, this method was well tolerated and resulted in a healing rate of
>95%15. It
should be noted, however, that this method is indicated for only specific
fracture types. In order to avoid the problems reported in the past with use
of a hybrid device, it is important to understand the appropriate indications
for its use. As the saying goes, one needs "the right tool for the right
job."
Localized pin-track infection has been the nemesis of external fixation and
one of the primary reasons many surgeons avoid its use. The anatomic sites
that are most prone to pin-related problems are those with a large soft-tissue
sleeve and those subject to motion of the soft tissues. Excessive motion of
the muscle and skin around the bone results in local inflammation that leads
to a pin-track infection and in turn can progress to infect the bone. What
appears to be clear to most experienced surgeons is that the most important
parameter is the control of soft-tissue motion. Stabilizing the soft tissues
around the pin to prevent motion is probably more important than the method or
agent of cleaning. There are numerous methods with which to stabilize the
skin. One of the best is application of a gentle compressive dressing between
the bar and skin. With this method, it is important to avoid excessive
pressure and skin necrosis.
Pin-care protocols range from doing nothing to washing the site of entry
three times a day with cotton swabs and peroxide. Temple and Santy performed a
comprehensive review of studies on pin care in the
literature22. They
found one randomized, controlled study in which saline solution, alcohol, and
no cleaning were compared, and no cleaning resulted in fewer infections.
Another study demonstrated no difference between daily and weekly pin
care23. There is
now sufficient evidence that elaborate pin care is not necessary and that
simple and occasional attention to the pins may be sufficient. Most
practitioners recommend daily pin care performed for personal hygiene reasons.
There is no evidence that any one modality or chemical works better than
another, but we recommend a non-tissue-toxic cleaner such as soap. It would
seem that pin site irritation leading to inflammation is a probable mechanism
that results in infection and, finally, loosening of the pin. Therefore,
minimizing mechanical skin motion may be more important than the frequency of
cleaning or type of cleaning
agents24
(Fig. 10).
We developed a pin-care protocol that has served us well but is not based
on scientific data. As previously described, when a pin is being inserted, the
soft-tissue compartment should be placed on stretch and the skin should be
released if needed so that there is no skin tension. The pin sites are covered
and, to ensure that there is no pistoning of the soft tissue, we use bolsters,
spacers, or sponges to stabilize it. The pin sites are left covered and are
not inspected for as long as the patient is in the intensive care unit. If the
pins are cleaned during the inpatient stay, we use saline solution or alcohol
and do not probe the tracks with cotton swabs. Nursing staff and aides do not
provide pin care. The pin sites are gently wiped with an alcohol pledget and
then covered. The surrounding skin is stabilized by placing a bolster between
the bar and skin that applies gentle pressure to the skin and prevents motion
with routine activity.
The patient is instructed to shower daily after he or she is discharged and
to clean the fixator with soap and water in the shower as part of a daily
routine. The skin and pins are dried with a clean towel, and the pin sites are
wiped with an alcohol pledget. The skin is then stabilized as described above.
Bath water, fresh-water lakes, and sea water are avoided.
Problems with pin-track infection should be managed as quickly as they are
identified. We use the classification of Checketts et
al.25,26.
While the literature often describes relatively high rates of "pin-track
infection," close inspection will demonstrate that the majority of
pin-related problems fall into the Checketts grade-I and II categories, which
are very mild. A problematic pin is one associated with ongoing exudates or
purulent discharge with surrounding inflammation and subsequent loosening.
When a pin site looks irritated, we first assess the nature of the pin care
being provided. We then check the stability of the pin in bone and of the
entire construct. If the pin or construct is loose, any and all pin care will
usually be futile. We stratify our pin problems in two ways, according to
stability and inflammation. Any pin that is unstable and associated with
inflammation is removed. Pins associated with inflammation and transudate that
are stable (Checketts grades I and II) are
retained25. We
begin by ensuring proper skin stability, and we frequently apply Bactroban
(mupirocin) ointment. Pins that are associated with inflammation and purulence
are at greater risk. In addition to all of the interventions provided for
grade-I and II problems, we add oral antibiotics in adequate doses (Keflex
[cephalexin], 500 mg four times a day, or Levaquin [levofloxacin], 500 mg
daily) because suboptimal antibiotics are not only ineffective but also can
lead to the development of resistant organisms
(Fig. 11). We also increase
the frequency of cleaning if there is accumulation of dried exudates. If after
such interventions there is no improvement, we then check the stability of the
pin again, and if it is loose we remove it. Also, as noted previously in our
description of the method of application, the use of three or four fixation
points in each segment provides the latitude of being able to remove one or
two pins during treatment without compromising the outcome or necessitating a
return to the operating room. With this methodology, we have substantially
limited the need to revise pins, and patients have tolerated fixators very
well.
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damage-control to definitive treatment. Advanced applications can be used to
treat deformity, infection, and fractures that are not healing. The poor
reputation of external fixation, especially in the United States, is due to
misunderstandings, misapplication, and mismanagement. The principles of
application and management are fairly straightforward and versatile. The
technique does require more attention than internal fixation, and careful
clinical and radiographic monitoring is needed. External fixation is not the
best treatment for the typical fracture, but its use can be of benefit in
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