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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_708_Библиотеки_им_академика_М_И_Перельмана
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51
Approaches for External Fixation
and Bridge Plate Fixation in the
Foot and Ankle
External Fixation of the Ankle and Foot
Bridging Fixation of the Foot
Introduction
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Although a wide variety of external fixators can be constructed, they
all consist of only two elements. Pins or wires are inserted into the
bone to anchor the external fixator to the skeleton. These pins or wires
are then connected to provide stability. Pins may be inserted by
transfixing the limb (transfixion pins), or most commonly they may
stop just beyond the far cortex of the bone into which they are inserted
(half pins). Wires always transfix the limb. Transfixion pins or wires
can be connected at both their ends; therefore, external fixators that
use these pins or wires provide the greatest stability. Because
transfixion pins or wires transfix the soft tissues on both sides of the
bone, they tether soft tissues more than half pins do. This makes it
difficult to mobilize joints above and below the external fixator.
Fixators using transfixion pins or wires are used in situations that
require the greatest stability, for example, distraction osteogenesis or
joint fusion.1 They are also used for the gradual correction of bone and
soft tissue deformity.
2
Skeletal pins are usually inserted through small open incisions in
the skin in a “blind” fashion, with little dissection of the soft tissues.
Exceptions occur where nerves are close to pin placement. Studies of
cross-sectional anatomy in cadaveric material reveal a number of
possible pin placements for any given bone in any given position.
Bridging internal plates can also be used in a similar fashion to
external fixators (as described above) but usually are meant for use
over an extended length of time. These plates are used to span areas of
significant injury to allow for healing and then secondary surgery is
undertaken for their removal once foot shape and alignment is
corrected.
There are three main uses for external fixators or bridging internal
plates in the foot and ankle:
1. External fixators may be used as a temporary way of
immobilizing a fracture in cases where the soft tissues are so
injured that immediate open surgery is impossible. These fixators
frequently span joints and the pins used are ideally placed outside
the zone of injury so that they do not interfere with subsequent
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definitive surgery. The most common application is in highenergy pilon fractures of the distal tibia. Bridging plates are not
used around the ankle but are used in the midfoot and forefoot.
2. Another common indication for the use of an external fixator or
bridging plate is open fractures. These injuries usually are
associated with fracture displacement, and the normal anatomy
frequently is distorted. Distortion of the normal anatomy or
normal anatomic variation may make apparently safe routes
hazardous and when skeletal pins are used, nerves and vessels
may be damaged as they course down the limb. Importantly, pin
placement should not interfere with the definitive soft tissue and
bony surgery for open fractures. For these reasons, only a few of
the safest pin placements are discussed for each bone in this
chapter.
3. Fine-wire fixators are used for the correction of bone and soft
tissue deformities. These applications require specialist
knowledge individualized to each patient and are beyond the
scope of this textbook.
The rigidity of an external fixator system that uses pins can be
modified in many ways.3 As mentioned above, transfixion pins
provide more stability than do half pins. Spreading the pins widely and
increasing their number also add to the rigidity of the system. Stability
is increased by utilizing larger pins as well as pins that are slightly
tapered (radial preload).
The number of bars used also increases stability; the closer the bars
are to the skin, the more stable the construct will be. Placement of the
pins is influenced not only by the underlying anatomy, but also by the
biomechanical requirements of the fixation system.
Finally, soft tissue damage also may dictate pin position.
Skin incisions for pin insertion should be generous because tight
skin around a pin inevitably leads to low-grade sepsis, which in turn
can cause pin loosening.
Bridge plates are most commonly used to protect reconstructions of
bone and soft tissue in the midfoot. They span the midfoot by being
applied from the hind part of the foot to the forefoot, bypassing the
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zone of injury. Plates can be applied using large incisions or inserted
via minimally invasive techniques. Spanning plates fix the foot in the
restored anatomic position with the arches rebuilt and length of the
medial and lateral columns of the foot maintained.
External Fixation of the Ankle and Foot
The bony prominences of the distal tibia, calcaneum, and first and fifth
metatarsals provide access for pin placement. The neurovascular bundle
running behind the medial malleolus should be avoided (Fig. 51-1). Half
pins should be used, except in the calcaneum, where transfixion pins
provide a stable pin construct to be placed for trauma-related problems (Fig.
51-2).
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Figure 51-1. Pin placement for external fixation around the ankle and foot.
Neurovascular structures behind the medial malleolus must be avoided. The
first metatarsal bone can be used for pin placement throughout the length of the
metatarsal, entering from medial and directing pins laterally. Half pins should be
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placed across both cortices of the first metatarsal. The fifth metatarsal may also
be used for half-pin placement, but pins are placed from lateral to medial.
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Figure 51-2. An external fixation frame that has proximal pins in the tibia and a
transverse pin through the calcaneum is called a Delta frame. Pins can be
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added that are placed into the first or fifth metatarsal (that connect to the Delta
frame) to dorsiflex the foot to maintain a foot flat position.
Half pins are placed in the distal tibia and in the first and fifth
metatarsals using a mini-open technique. The calcaneal pin is a transfixion
pin posterior and distal to the neurovascular bundle. The calcaneal pin
should be placed from medial to lateral to avoid injury to the neurovascular
bundle. The pin in the first metatarsal is placed perpendicular to the long
axis of the first ray but distal to the tibialis anterior tendon (Fig. 51-3).
The pin in the fifth metatarsal is placed perpendicular to the long axis of
the fifth ray with care as the bone is small and easily missed with poor
technique (Fig. 51-4). Pins in the first and/or the fifth ray allow the foot and
ankle to be placed in a safe neutral position for an extended period as soft
tissue and bone care continues.
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Figure 51-3. The first metatarsal can be used for external fixation with an
incision placed longitudinally along the whole length of the bone.
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Figure 51-4. The fifth metatarsal may also be used for half-pin placement, but
pins are placed from lateral to medial.
Bridging Fixation of the Foot
The approaches and use of the bridging internal fixation plate depend upon
the joints that need to be spanned while soft tissues and bony structures are
healing. The most common application is the spanning plate that traverses
the midfoot laterally, going from the calcaneum to the fourth metatarsal
supporting the injured midfoot (lateral column) of the foot (Fig. 51-5).4 The
medial spanning plate is used less commonly but can be placed to span
from the talus to the first metatarsal thus protecting the medial column
(medial midfoot) (Fig. 51-6).
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