Principles of Malunions

Evaluation of limb alignment involves assessment of the
frontal plane mechanical axis of the entire limb rather than single
bones.³⁵,⁴⁵,⁴⁷,⁷⁷,⁷⁸,⁹⁰
In the lower extremity, the frontal plane mechanical axis of the entire
limb is evaluated using the weight-bearing AP 51-inch alignment
radiograph with the feet pointed forward (neutral rotation).⁴¹,⁴⁹,⁸²
Mechanical axis deviation (MAD) is measured as the distance from the
knee joint center to the line connecting the joint centers of the hip
and ankle. The hip joint center is located at the center of the femoral
head. The knee joint center is half the distance from the nadir between
the tibial spines to the apex of the intercondylar notch on the femur.
The ankle joint center is the center of the tibial plafond.

Normally, the mechanical axis of the lower extremity lies 1 mm to 15 mm medial to the knee joint center (Fig. 26-3). If the limb mechanical axis is outside this range, the deformity is described as MAD (see Fig. 26-3).
MAD greater than 15 mm medial to the knee midpoint is varus
malalignment; any MAD lateral to the knee midpoint is valgus
malalignment.

The anatomic and mechanical axes of each of the long
bones are assessed in both the frontal plane (AP radiographs) and
sagittal plane (lateral radiographs). The anatomic axes are defined as
the line that passes through the center of the diaphysis along the
length of the bone. To identify the anatomic axis of a long bone, the
center of the transverse diameter of the diaphysis is identified at
several points along the bone. The line that

passes through these points represents the anatomic axis (Fig. 26-4).

In a normal bone, the anatomic axis is a single straight
line. In a malunited bone with angulation, each bony segment can be
defined by its own anatomic axis with a line through the center of the
diameter of the diaphysis of each bone segment representing the
respective anatomic axis for that segment (Fig. 26-5). In bones with multiapical or combined deformities, there may be multiple anatomic axes in the same plane.

The mechanical axis of a long bone is defined as the
line that passes through the joint centers of the proximal and distal
joints. To identify the mechanical axis in a long bone, the joint
centers are connected by a line (Fig. 26-6). The mechanical axis of the entire lower extremity was described above under the heading “Limb Alignment.”

Joint orientation describes the relation of a joint to
the respective anatomic and mechanical axes of a long bone. Joint
orientation lines are drawn on the AP and lateral radiographs in the
frontal and sagittal planes, respectively.

Hip orientation may be assessed in two ways in the
frontal plane. The trochanter-head line connects the tip of the greater
trochanter with center of the hip joint (the center of the femoral
head). The femoral neck line connects the hip joint center with a
series of points which bisect the diameter of the femoral neck.

Knee orientation is represented in the frontal plane by
joint orientation lines at the distal femur and the proximal tibia. The
distal femur joint orientation line is drawn tangential to the most
distal points of the femoral condyles. The proximal tibial joint
orientation line is drawn tangential to the subchondral lines of the
medial and lateral tibial plateaus. The angle between these two knee
joint orientation lines is called the joint line congruence angle
(JLCA), which normally varies from 0 degrees to 2 degrees medial JLCA
(i.e., slight knee joint varus). A lateral JLCA represents valgus
malorientation of the knee, and a medial JLCA of 3 degrees or greater
represents varus malorientation of the knee.

Knee orientation is represented in the sagittal plane by
joint orientation lines at the distal femur and the proximal tibia. The
sagittal distal femur joint orientation line is drawn through the
anterior and posterior junctions of the femoral condyles and the
metaphysis. The sagittal proximal tibial joint orientation line is
drawn tangential to the subchondral lines of the tibial plateaus.

Malorientation of the knee joint produces malalignment,
but limb malalignment (MAD outside the normal range) is not necessarily
due to knee joint malorientation.

Ankle orientation is represented in the frontal plane by
a line drawn through the subchondral line of the tibial plafond. Ankle
orientation is represented in the sagittal plane by a line drawn
through the most distal points of the anterior and posterior distal
tibia.

The relation between the anatomic axes or the mechanical
axes and the joint orientation lines can be referred to as joint
orientation angles described using standard nomenclature (Table 26-1 and Fig. 26-7).

In order to draw a joint orientation angle in the lower
extremity, begin by drawing a joint orientation line. Next, identify
the joint center, as the joint center will always lie on the mechanical
axis and the joint orientation line. The mechanical axis line of the
segment near the joint can be drawn using one of three methods: (i)
using the population mean value for that particular joint orientation
angle; (ii) using the joint orientation angle of the contralateral
extremity, assuming it is normal; or (iii) by extending the mechanical
axis of the neighboring bone.

For example, in order to draw the mechanical lateral
distal femoral angle (mLDFA) in a femur with a frontal plane deformity,
the steps would be as follows. Step 1: Draw the distal femoral joint
orientation line. Step 2: Start at the joint center and draw an
88-degree mLDFA (population normal mean value), which will define the
mechanical axis of the distal femoral segment, or draw the mLDFA which
mimics the contralateral distal femur (if normal), or extend the
mechanical axis of the tibia proximally (if normal) to define the
distal femoral mechanical axis.

The intersection of the proximal axis and distal axis of a deformed bone is called the CORA (Fig. 26-8), which is the point about which a deformity may be rotated to achieve correction.²²,³⁰,³⁴,⁴⁶,⁷²,⁷³,⁷⁶,⁷⁷,⁷⁸,⁸⁹
The angle formed by the two axes at the CORA is a measure of angular
deformity in that plane. Either the anatomic or mechanical axes may be
used to identify the CORA, but these axes cannot be mixed. For
diaphyseal malunions, the anatomic axes are most convenient. For
juxta-articular (metaphyseal, epiphyseal) deformities, the axis line of
the short segment is constructed using one of the three methods
described above.

To define the CORA, the proximal axis and distal axis of
the bone are identified, and then the orientations of the proximal and
distal joints are assessed. If the intersection of the proximal and
distal axes lies at the point of obvious deformity in the bone and the
joint orientations are normal, the intersection point is the CORA and
the deformity is uniapical (in the respective plane). If their
intersection lies outside the point of obvious deformity or either
joint orientation is abnormal, either a second CORA exists in that
plane and the deformity is multiapical or a translational deformity
exists in that plane, which is usually obvious on the radiograph.

The CORA is used to plan the operative correction of
angular deformities. Correction of angulation by rotating the bone
around a point on the line that bisects the angle of the CORA (the
“bisector”) ensures realignment of the anatomic and mechanical axes
without introducing an iatrogenic translational deformity.³⁴ The bisector is a line that passes through the CORA and bisects the angle formed by the proximal and distal axes (see Fig. 26-8).⁷²
Angular correction along the bisector results in complete deformity
correction without the introduction of a translational deformity.¹⁰,⁷³,⁷⁵,⁷⁷,⁷⁸
All points that lie on the bisector can be considered to be CORAs
because angulation about these points will result in realignment of the
deformed bone (see “Treatment—Osteotomies”).

Note that the proximal half of the mechanical axis for
the femur normally lies outside the bone, so the CORA identified using
the mechanical axis of the femur may lie outside the bone as well. By
contrast, if the CORA identified using the anatomic axis of the femur
or either axis of the tibia lies outside the bone, then a multiapical
deformity exists (see Fig. 26-8).

Deformities involving length include shortening and
overdistraction and are characterized by their direction and magnitude.
They are measured from joint center to joint center in centimeters on
plain radiographs and compared to the contralateral normal extremity,
using an x-ray marker to correct for magnification (Fig. 26-9).⁹¹
Shortening after an injury may result from bone loss (from the injury
or débridement) or overriding of the healed fracture fragments.
Overdistraction at the time of fracture fixation may result in a healed
fracture with overlengthening of the bone.

Deformities involving angulation are characterized by
their magnitude and the direction of the apex of angulation. Angulation
deformity of the diaphysis is often associated with limb malalignment
(MAD), as described above. Angulation deformities of the metaphysis and
epiphysis (juxta-articular deformities) can be difficult to
characterize. In particular, the angle formed by the intersection of a
joint orientation line and the anatomic or mechanical axis of the
deformed bone should be measured. When the angle formed differs
markedly from the contralateral normal limb (or normal values when the
contralateral limb is abnormal), a juxta-articular deformity is present.¹⁰,⁷⁵,⁷⁸ The identification of the CORA is key in characterizing angular deformities and planning their correction.

Pure frontal or sagittal plane deformities are simple to
characterize; the angular deformity appears only on the AP or lateral
radiograph, respectively. If, however, the AP and lateral radiographs
both appear to have angulation with CORAs at the same level on both
views, the orientation of the angulation deformity is in an oblique
plane (Fig. 26-10). Characterization of the
magnitude and direction of oblique plane deformities can be computed
from the AP and lateral x-ray measures using either the trigonometric
or graphic method.¹⁸,³⁷,⁷² Using the trigonometric method, the magnitude of an oblique plane angular deformity is

and the orientation (relative to the frontal plane) of an oblique plane deformity is

Using the graphic method, the magnitude of an oblique plane angular deformity is

and the orientation (relative to the frontal plane) of an oblique plane deformity is

The graphic method, based on the Pythagorean Theorem,
approximates the exact trigonometric method. The error of approximation
for angular deformities using the graphic method is less than 4 degrees
unless the frontal and sagittal plane magnitudes are both greater than
45 degrees.¹⁰,⁴⁶,⁷²,⁷⁵,⁷⁷,⁷⁸

In the case that the CORA is at a different level on the
AP and lateral radiographs, a translational deformity is present in
addition to an angulation deformity (Fig. 26-11).

A multiapical deformity is defined by the presence of
more than one CORA on either the AP or lateral radiograph (or both). In
a multiapical deformity without translation, one of the joints will
appear maloriented relative to the anatomic axis of the respective
segment. For multiapical deformity, the anatomic

axis
of the segment that has the joint malorientation provides a third line
that crosses both of the existing lines. These intersections are the
sites of the multiple CORAs (see Fig. 26-8B).

A rotational deformity occurs about the longitudinal
axis of the bone. Rotational deformities are described in terms of
their magnitude and the position (internal or external rotation) of the
distal segment relative to the proximal segment. Identification of a
rotational deformity and quantification of the magnitude can be done
using clinical measurements,¹⁰¹ axial computed tomography (Fig. 26-12),¹² or AP and lateral radiographs with either trigonometric calculation or graphical approximation.⁷²
While axial computed tomography and radiographic methods allow for more
precise measurement of rotational deformities, clinical examination
often results in measures of sufficient accuracy to allow for adequate
correction.¹⁰¹

To measure tibial malrotation using clinical
examination, the position of the foot axis, as indicated by a line
running from the second toe through the center of the calcaneus, is
compared to the projection of either the femoral or the tibial anatomic
axis. To use the femoral axis, the patient is positioned prone or sits
with the knee flexed to 90 degrees. The examiner measures the deviation
of the foot axis from the line of the femoral axis; any deviation is
considered to represent tibial malrotation. To use the tibial axis, the
patient stands with the patella facing anteriorly (i.e., aligned in the
frontal plane). To measure tibial malrotation, the examiner measures
the deviation of the foot axis from the anterior projection of the
tibial anatomic axis in the sagittal plane; any deviation of the foot
axis from the tibial anatomic axis is considered to represent tibial
malrotation.

To measure a femoral rotational deformity using clinical
examination, the patient is positioned prone with the knee flexed to 90
degrees and the femoral condyles parallel to the examination table. The
femur is passively rotated internally and externally by the examiner,
and the respective angular excursions of the tibia are measured.
Asymmetry of rotation in comparison to the opposite side indicates a
femoral rotational deformity. If the patient also has a tibial
angulation deformity, the tibia will not be perpendicular to the
examination table when the femoral condyles are so positioned; tibial
angulation deformity will cause an apparent asymmetry in femoral
rotation. In this case, the rotational excursions of the tibia must be
adjusted for the magnitude of the tibial angular deformity to avoid an
incorrect assessment of femoral rotation.

Translational deformities may result from malunion
following either a fracture or an osteotomy. Translational deformities
are characterized by their plane, direction, magnitude, and level. The
direction of translational deformities is described in terms of the
position of the distal segment relative to the proximal segment
(medial, lateral, anterior, posterior), except for the femoral and
humeral heads where the description is the position of the head
relative to the shaft. Translational deformities may occur in an
oblique plane, and trigonometric or graphical methods similar to those
described for characterizing angulation deformities may be used to
identify the plane and direction of the deformity.¹⁸,³⁷,⁷²
Magnitude of translation is measured as the horizontal distance from
the proximal segment’s anatomic axis to the distal segment’s anatomic
axis at the level of the proximal end of the distal segment (Fig. 26-13).

The type of wedge osteotomy is determined by the
location of the osteotomy relative to the locations of the CORA and the
correction axis. When the CORA and correction axis are in the same
location (to avoid translational deformity), they may lie on the cortex
on the convex side of the deformity, on the cortex on the concave side
of the deformity, or in the middle of the bone (Fig. 26-15).

When the CORA and correction axis lie on the convex
cortex of the deformity, the correction will result in an opening wedge
osteotomy (see Fig. 26-15). In an opening
wedge osteotomy, the cortex on the concave side of the deformity is
distracted to restore alignment, opening an empty wedge that traverses
the diameter of the bone. An opening wedge osteotomy also increases
bone length.

When the CORA and correction axis lie in the middle of
the bone, the correction distracts the concave side cortex and
compresses the convex side cortex. A bone wedge is removed from only
the convex side to allow realignment. This neutral wedge osteotomy (see
Fig. 26-15) has no effect on bone length.

When the CORA and correction axis lie on the concave
cortex of the deformity, the correction will result in a closing wedge
osteotomy (see Fig. 26-15). In a closing wedge
osteotomy, the cortex on the convex side of the deformity is compressed
to restore alignment; this requires removal of a bone wedge across the
entire bone diameter. A closing wedge osteotomy also decreases bone
length (resulting in shortening).

These principles of osteotomy also hold true when the
osteotomy is located proximal or distal to the mutual site of the CORA
and correction axis. As stated above, realignment in these

cases
occurs via angulation and translation. When the CORA and correction
axis are not at the same point and the osteotomy is proximal or distal
to the CORA, the correction maneuver results in excess translation and
an iatrogenic translational deformity.

The type of dome osteotomy is also determined by the
location of the CORA and the correction axis relative to the osteotomy.
In contrast to a wedge osteotomy, however, the osteotomy site can never
pass through the mutual CORA-correction axis (Fig. 26-16). Thus, translation will always occur with deformity correction using a dome osteotomy.

Ideally, the CORA and correction axis are mutually
located such that the angulation and obligatory translation that occurs
at the osteotomy site results in realignment. Attempts at realignment
when the CORA and correction axis are not mutually located results in a
translational deformity (see Fig. 26-16).
Similar to wedge osteotomy, the CORA and correction axis may lie on the
cortex on the convex side of the deformity, on the cortex on the
concave side of the deformity, or in the middle of the bone.

The principles guiding wedge osteotomies are also true
for dome osteotomies. When the CORA and correction axis lie on the
convex cortex of the deformity, the correction will result in an
opening dome osteotomy (Fig. 26-17). The
translation that occurs in an opening dome osteotomy increases final
bone length. When the CORA and correction axis lie in the middle of the
bone, the correction will result in a neutral dome osteotomy. A neutral
dome osteotomy has no effect on bone length. When the CORA and
correction axis lie on the concave cortex of the deformity, the
correction will result in a closing dome osteotomy. The translation
that occurs in a closing dome osteotomy decreases final bone length.
Unlike wedge osteotomies, the movement of one bone segment on the other
is rarely impeded, so removal of bone is not typically required unless
the final

configuration results in significant overhang of the bone beyond the aligned bone column.

Acute distraction or compression methods obtain
immediate correction of limb length by acute lengthening with bone
grafting or acute shortening, respectively. The extent of acute
lengthening or shortening that is possible is limited by the soft
tissues (soft tissue compliance, surgical and open wounds, and
neurovascular structures).

Acute distraction treatment methods involve distracting
the bone ends to the appropriate length, applying a bone graft, and
stabilizing the construct to allow incorporation of the graft. Options
for treating length deformities include the use of: (i) autogenous
cancellous or cortical bone grafts; (ii) vascularized autografts; (iii)
bulk or strut cortical allografts; (iv) mesh cagebone graft constructs;
and (v) synostosis techniques. A variety of internal and external
fixation treatment methods may be used to stabilize the construct
during graft incorporation.⁹ The amount of shortening that requires lengthening correction is uncertain.³⁸,⁶⁵,¹⁰²
In the upper extremity, up to 3 to 4 cm of shortening is generally well
tolerated, and restoring length when shortening exceeds this value have
been reported to improve function.¹,¹⁹,⁵⁹,⁷¹,⁸¹,⁹⁶,¹⁰⁴,¹⁰⁷
In the lower extremity, up to 2 cm of shortening may be treated with a
shoe lift; tolerance for a 2 to 4 cm shoe lift is poor for most
patients, and most patients with shortening of greater than 4 cm will
benefit from restoration of length.⁷,⁸,³¹,⁶⁴,¹⁰²,¹⁰⁹

Acute compression methods are used to correct
overdistraction by first resecting the appropriate length of bone and
then stabilizing the approximated bone ends under compression. For the
paired bones of the forearm and leg, the unaffected bone

requires
partial excision to allow shortening and compression of the affected
bone. For example, partial excision of the intact fibula is necessary
to allow shortening and compression of the tibia.

Gradual correction techniques for length deformities typically use tensioned-wire (Ilizarov) external fixation,³,¹⁶,⁵⁰,⁵⁹,⁶⁰,⁶²,⁷⁴,¹⁰²,¹⁰⁴,¹⁰⁷ although gradual lengthening using conventional monolateral external fixation has been described,⁷⁰,⁹³,⁹⁴ and an intramedullary nail that provides a continuous lengthening force has recently been developed.¹⁷,⁴³,⁴⁴
The most common form of gradual correction is gradual distraction to
correct limb shortening. Gradual correction methods for length
deformities can also be used to correct associated angular,
translational, or rotational deformities simultaneously while restoring
length.

Gradual distraction involves the creation of a
corticotomy (usually metaphyseal) and distraction of the bone segments
at a rate of 1 mm per day using a rhythm of 0.25 mm of distraction
repeated four times per day. The bone formed at the distraction site is
formed through the process of distraction osteogenesis, as discussed
below in the “Ilizarov Techniques” section.

Correction of angulation deformities involves making an osteotomy, obtaining realignment of the bone segments, and securing

fixation during healing. The correction may be made acutely and then
stabilized using a number of internal or external fixation methods.²⁸,³⁹
Alternatively, the correction may be made gradually using external
fixation to both restore alignment and provide stabilization during
healing.²⁸,¹⁰⁵

Angulation deformities in the diaphysis are most
amenable to correction using a wedge osteotomy at the same level as the
correction axis and the CORA. For juxta-articular angulation
deformities, however, the correction axis and the CORA may be located
too close to the respective joint to permit a wedge osteotomy. Thus,
juxta-articular angulation deformities may require a dome osteotomy
with location of the osteotomy proximal or distal to the level of the
correction axis and the CORA.

Correction of a rotational deformity requires an
osteotomy and rotational realignment followed by stabilization.
Stabilization may be accomplished using internal or external fixation
following acute correction, or external fixation may be used to
gradually correct the deformity. The level for the osteotomy, however,

can
be difficult to determine. While the level of the deformity is obvious
in the case of an angulated malunion, the level of deformity in
rotational limb deformities is often difficult to determine.
Consequently, other factors, including muscle and tendon line of pull,
neurovascular structures, and soft tissues, are usually considered to
determine the level of deformity and level of osteotomy for correction
of a rotational deformity.³²,⁵⁶,⁵⁷,⁷²,⁸⁰,¹⁰⁰

Translational deformities may be corrected in one of
three ways. First, a single transverse osteotomy may be made to restore
alignment through pure translation without angulation; the transverse
osteotomy does not have to be made at the level of the deformity (Fig. 26-18).
Second, a single oblique osteotomy may be made at the level of the
deformity to restore alignment and gain length. Third, a translational
deformity can be represented as two angulations with identical
magnitudes but opposite directions. Therefore, two wedge osteotomies at
the level of the respective CORAs and angular corrections of equal
magnitudes in opposite directions may be used to correct a
translational deformity. It should be noted that the osteotomy types
used in this third method (opening, closing, or neutral) will affect
final bone length. Internal or external fixation may be used to provide
stabilization following acute correction of translational deformities,
or gradual correction may be carried out using external fixation.

Combined deformities are characterized by the presence of two or more types of deformity in a single bone³⁷,⁴⁰
Treatment planning begins with identifying and characterizing each
deformity independent from the other deformities. Once all deformities
have been characterized, they are assessed to determine which require
correction to restore function. Correction of all of the deformities
may be unnecessary; for example, small translational deformities or
angulation deformities in the sagittal plane may not interfere with
limb function and may remain untreated. Once those deformities
requiring correction are identified, the treatment plan outlines the
order and method of correction for each deformity.

In many instances, a single osteotomy can be used to
correct two deformities. For example, a combined
angulation-translational deformity can be corrected using a single
osteotomy at

the
level of the apex of the angulation deformity. This method restores
alignment and congruency of the medullary canals and cortices of the
respective bone segments (Fig. 26-19).
The deformities are then reduced one at a time—reducing translation and
then angulation, for instance. Consequently, stabilization can be
achieved using an intramedullary nail, as well as a number of other
internal fixation and external fixation methods.

Combined angulation-translation deformities can also be
treated as multiapical angulation deformities with an osteotomy through
either or both CORAs in the frontal and sagittal planes. While this
method restores alignment of the bone’s mechanical axis, it can also
result in incomplete bone-to-bone contact and incongruence of the bone
segments’ medullary canals and cortices. As a result, stabilization
cannot be achieved using an intramedullary nail and other internal
fixation and external fixation methods are required to stabilize the
bone segments.

A combined angulation-rotational deformity can be
corrected by a single rotation of the distal segment around an oblique
axis that represents the resolutions of both the component angulation
axis and rotation axis (Fig. 26-20).⁶⁶ The direction

and magnitude of the combined angulation-rotational deformity are both
characterized in this oblique axis. The angle of the oblique correction
axis, which is perpendicular to the plane of the necessary osteotomy,
can be approximated using trigonometry (axis angle = arctan
[rotation/angulation]; orientation of plane of osteotomy = 90- axis
angle).

This single osteotomy is made at a location such that it
passes through the level of the CORA of the angulation deformity (i.e.,
the bisector of the axes of the proximal and distal segments). Rotation
of the distal segment about this CORA in the plane of the osteotomy
results in realignment; opening and closing wedge corrections can also
be achieved by using the CORA located on the respective cortex.
Rotation of the distal segment in the plane of the osteotomy but not
about a CORA will lead to a secondary translational deformity. This
secondary deformity can be corrected by reducing the translation after
rotation is completed. Locating the level of the osteotomy distal to
the level of the CORA and correcting the secondary translational
deformity can be used to correct a combined deformity if locating the
osteotomy at the level of the CORA is impractical, such as would occur
if the osteotomy would violate a growth plate or place soft tissues or
neurovascular structures at risk.

Diaphyseal deformities involve primarily cortical bone
in the central section of long bones. Characterizing deformities is
straightforward, as angulation and translational deformities are
usually obvious on plain radiographs. In addition, the use of wedge
osteotomies through the CORA for deformity correction is generally
achievable, thus allowing reduction of the deformity without concerns
about inducing secondary translational deformities. By virtue of their
relatively homogenous morphology, diaphyseal deformities are amenable
to a wide array of fixation methods following correction.
Intramedullary nail fixation is preferable when practical (Fig. 26-21).

Periarticular deformities located in the metaphysis and
epiphysis are more difficult to identify, characterize, and treat. In
addition to the juxta-articular deformities of length, angulation,
rotation, and translation and the presence of joint malorientation,
there may also be malreduction of articular surfaces and compensatory
joint deformities, such as soft tissue contractures and fixed joint
subluxation or dislocation. Identification, characterization, and
prioritization of each component of the deformity are critical to
forming a successful treatment plan.

Acute correction of periarticular deformities is most
often accomplished using plate and screw fixation or external fixation.
Gradual correction may be accomplished using external fixation (Fig. 26-22).

The advantages of plate and screw fixation include
rigidity of fixation, versatility for various anatomic locations and
situations (e.g., periarticular deformities), correction of deformities
under direct visualization, and safety following failed or temporary
external fixation. Disadvantages of the method include extensive soft
tissue dissection, limitation of early weight bearing and

function,
and inability to correct significant shortening deformity. A variety of
plate types and techniques is available, and these are presented in the
chapters covering specific fracture types. In cases of deformity
correction with poor bone-to-bone contact following reduction, however,
other methods of skeletal stabilization should be considered.

Locking plates have screws with threads that lock into
threaded holes on the corresponding plate. This locking effect creates
a fixed-angle device, or “single-beam” construct, because no motion
occurs between the screws and the plate.¹⁵,²⁴,⁴²
In contrast to traditional plate-and-screw constructs, the locked
screws resist bending moments and the construct distributes axial load
across all of the screw-bone interfaces.²⁴,⁴²
As compared to compression plating where healing is by direct osteonal
bridging, locked plating performed without compression results in
healing via callus formation.²⁴,⁴⁸,⁷⁹,⁹⁵,¹¹⁰
Due to the inherent axial and rotational stability with locked devices,
obtaining contact between the plate and the bone is not necessary; the
construct can be thought of as an external fixator placed within the
body. Consequently, periosteal damage and microvascular compromise are
minimal. Locking plates are considerably more expensive than
traditional plates and should be used in deformity cases that are not
amenable to traditional plate-and-screw fixation.¹⁵

Intramedullary nail fixation is particularly useful in
the lower extremity because of the strength and load-sharing
characteristics of intramedullary nails. This method of fixation is
ideal for cases where diaphyseal deformities are being corrected (Fig. 26-23).
The method may also be useful for deformities at the
metaphyseal-diaphyseal junction. Intramedullary implants are excellent
for osteopenic bone where screw purchase may be poor.

Ilizarov techniques^* have many advantages,
including that they: (i) are primarily percutaneous, minimally
invasive, and typically requires only minimal soft tissue dissection;
(ii) can promote the generation of osseous tissue; (iii) are versatile;
(iv) can be used in the presence of acute or chronic infection; (v)
allow for stabilization of small intra-articular or periarticular bone
fragments; (vi) allow simultaneous deformity correction and enhancement
of bone healing;³,⁴,⁵,⁹,¹³,³⁶,⁵⁴,⁵⁵
(vii) allow immediate weight bearing and early joint function; (viii)
allow augmentation or modification of the treatment as needed through
frame adjustment; and (ix) resist shear and rotational forces while the
tensioned wires allow the “trampoline effect” (axial loadingunloading)
during weight-bearing activities.

The Ilizarov external fixator can be used to reduce and
stabilize virtually any type of deformity, including complex combined
deformities, and restore limb length in cases of limb foreshortening. A
variety of treatment modes can be employed using the Ilizarov external
fixator, including distraction-lengthening, and multiple sites in a
single bone can be treated simultaneously. Monofocal lengthening
involves a single site undergoing distraction. Bifocal lengthening
denotes that two lengthening sites exist (Fig. 26-24).

Distraction-Lengthening. The bone formed at the
corticotomy site in distraction-lengthening Ilizarov treatment occurs
by distraction

osteogenesis (Fig. 26-25).⁵,⁶,²⁰,⁵⁰,⁶⁷
Distraction produces a tension-stress effect that causes neovascularity
and cellular proliferation in many tissues, including bone regeneration
primarily through intramembranous bone formation. Corticotomy and
distraction osteogenesis result in profound biological stimulation,
similar to bone grafting. For example, Aronson⁴
reported a nearly ten-fold increase in blood flow following corticotomy
and lengthening at the proximal tibia distraction site relative to the
control limb in dogs as well as increased blood flow in the distal
tibia.

A variety of mechanical and biologic factors affect
distraction osteogenesis. First, the corticotomy or osteotomy must be
performed using a low-energy technique to minimize necrosis. Second,
distraction of the metaphyseal or metaphyseal-diaphyseal regions has
superior potential for regenerate bone formation relative to diaphyseal
sites. Third, the external fixator construct must be very stable.
Fourth, a latency period of 7 to 14 days following the corticotomy and
prior to beginning distraction is recommended. Fifth, since the
formation of the bony regenerate is slower in some patients, the
treating physician should monitor the progression of the regenerate on
plain radiographs and adjust the rate and rhythm of distraction
accordingly. Sixth, a consolidation phase in which external fixation
continues in a static mode following restoration of length that
generally lasts 2 to 3 times as long as the distraction phase is
required to allow maturation and hypertrophy of the regenerate.

Complex Combined Deformities. All bone deformities can
be characterized by describing the position of one bone segment
relative to another in terms of angular rotations in each of three
planes and linear displacements in each of three axes. Using the
methods described above, complex deformities can be characterized using
magnitudes for each of these six parameters. Directions of the
rotations or displacements are defined as positive and negative
relative to the anatomic position. Anterior, right, and superior
displacements are defined as positive values. Positive rotation is
defined by the right-hand rule: with the thumb pointed in the positive
direction along the respective axis (defined identically to the
displacement descriptions), the curled fingers indicate the direction
of positive rotation (Fig. 26-26). For example,
angulation in the frontal plane is rotation about an AP axis. With
anterior defined as the positive direction for this axis,
counterclockwise rotation (to an examiner who is face to face with the
patient) is positive and clockwise rotation is negative.

Complex combined deformities often require gradual
correction to allow adaptation of not only the bone but also
surrounding soft tissues and neurovascular structures. The modern
Ilizarov hardware system uses different components (hinges, threaded
rods, rotation-translation boxes) to achieve correction of multiple
deformity types in a single bone. Alternatively, the Taylor Spatial
Frame (Fig. 26-27), which uses six telescopic struts, can be used to correct complex combined deformities.²,²⁵,²⁶,²⁷,²⁹,⁵⁸,⁶²,⁶³,⁶⁸,⁶⁹,⁸³,⁸⁴,⁸⁵,⁸⁶,⁸⁷,⁹⁷,⁹⁸,¹⁰³,¹⁰⁶,¹⁰⁸,¹¹¹,¹¹²
A computer program is used in treatment planning to determine strut
lengths for the original frame construction. The rings of the external
fixator frame are attached perpendicular to the respective bone
segments and the struts are gradually adjusted to attain neutral frame
height (i.e., rings in parallel). Any residual deformity is then
corrected by further adjusting the struts.

Correction can be simultaneous, in which all deformities
are corrected at the same time, or sequential, in which some
deformities (e.g., angulation-rotation) are corrected before others
(e.g., translations). The rate at which correction occurs must be
determined on a patient-by-patient basis and depends on the type and
magnitude of deformity, the potential effects on the soft tissues, the
health and healing potential of the patient, and the balance between
premature consolidation and inadequate regenerate formation.