Case Series
Midfoot and Hindfoot Charcot Joint Deformity Correction with Hexapod-assisted Circular External Fixation
Noman A Siddiqui1* and Amanda Pless2
1Department of Podiatric Surgery, Rubin Institute for Advanced Orthopedics, International Center for Limb Lengthening, Sinai Hospital of Baltimore, 2401 W. Belvedere Ave, Baltimore MD, 21215, USA
2Our Lady of Lourdes Memorial Hospital, 169 Riverside Drive, Binghamton, NY 13905, USA
*Corresponding author: Noman A Siddiqui, Department of Podiatric Surgery, Northwest Hospital, Rubin Institute for Advanced Orthopedics, International, Center for Limb Lengthening, Sinai Hospital of Baltimore, 2401 W. Belvedere Ave, Baltimore MD, 21215, USA
Published: 25 Apr, 2017
Cite this article as: Siddiqui NA, Pless A. Midfoot and
Hindfoot Charcot Joint Deformity
Correction with Hexapod-assisted
Circular External Fixation. Clin Surg.
2017; 2: 1430.
Abstract
Charcot Neuroarthropathy (CN) is a debilitating condition that results in complex foot and ankle
deformity. Loss of normal pedal architecture can cause gait dysfunction as well as soft-tissue
compromise and limb loss. Foot and ankle surgeons have treated CN with and without operative
intervention. Operative techniques to treat midfoot and hindfoot deformities with internal and
external fixation have been described in the literature. Despite a lack of consensus as to the fixation
method, articles have attempted to identify features that necessitate operative intervention. This
article proposes recommendations for surgeons to utilize when correcting CN with hexapodassisted
circular external fixation.
Keywords: Charcot neuroarthropathy; Ilizarov external fixation; Hexapod; Midfoot charcot;
Hindfoot charcot
Key Points
• Charcot deformity of the midfoot and hindfoot is complex.
• Operative treatment should be reserved for feet that are unstable, non-braceable, have
wounds, and are at high risk for amputation.
• Hexapod-assisted circular external fixation can be used in feet with good bone stock and
a large angular deformity.
• Surgery should be performed in two stages to obtain and maintain correction.
Charcot Neuroarthropthy (CN) is a debilitating and aggressive process affecting the bones, joints,
and soft tissues of the foot and ankle. The process can ultimately lead to deformity and disfigurement
of the affected foot and ankle. The prevalence of the disease is between 0.08% and 7.5% in patients
with diabetes mellitus [1]. The pathogenesis of the disease process is thought to be multifactorial in
nature resulting in a localized inflammatory state that leads to bony destruction, dislocation, and
subluxation [2]. These challenging cases require surgical intervention for reconstruction of the foot
and ankle to address instability, major osseous destruction, and deformity that cause ulceration and
infection. The goals of surgical intervention include creation of a stable, plantigrade foot that is both
ulcer- and infection-free and ultimately able to be placed in a brace for ambulation [3].
In recent years, many studies have been published on the efficacy and indications for various
Charcot deformity treatments including conservative methods, internal fixation, “super constructs,”
external fixation, and a hybrid of internal and external fixation methods [2,4,5]. While no definitive
consensus has yet been reached as to the superior method of fixation, attempts have been made to
discuss the rationale for various fixation methods [6,7]. One method of fixation that has gained
more attention is hexapod-assisted circular external fixation. The principles of traditional Ilizarov
circular fixation are used in conjunction with a software program to guide six-axis correction. The
goal of this article is to assist surgeons in identifying patients for Charcot reconstruction of the
midfoot and hindfoot with a hexapod-assisted circular frame.
Classification of Charcot Neuroarthropathy
Several classification systems for CN staging have been presented throughout the years. In
1966, Sidney Eichenholtz developed a three-stage system based upon radiographic evaluation [8].
Stage I, the developmental stage, consisted of bony debris, fragmentation, and dislocation. Stage II, coalescence stage, included absorption of fine debris, sclerosis, and fusion of fragments. Stage III, reconstruction and reconstitution
stage, consisted of lessened sclerosis, rounding of fragments, and
attempts at reformation of joint architecture [9].
With greater imaging modalities available today, anatomic
classifications are widely utilized, especially those of Sanders and
Frykberg [10], Brodsky and Rouse [11], and Schon [12]. The Schon
classification [12] is divided into four types based upon anatomic
location of deformity: Lisfranc, naviculocuneiform, perinavicular,
and transverse tarsal. Additionally, three stages of degree of collapse
in the sagittal plane on weight bearing radiographs are included. Stage
A shows the least degree of collapse (i.e., above the level of the plantar
surface of the foot). In stage B, the deformity collapses to the level
of the plantar surface. In stage C, the midfoot has attained a rocker
bottom deformity below the plantar surface of the foot and is prone
to ulceration [12].
Indications for Use of External Fixation
Benefits of surgical intervention via static and dynamic circular
external fixation have been well documented in patients with CN
deformity. Indications include the following:
• Midfoot/hindfoot/ankle instability
• Non-reducible bony deformity
• Bony defect (with or without osteomyelitis)
• Soft-tissue ulceration (with or without infection)
• Ambulatory dysfunction that cannot be corrected through
bracing
The indications for hexapod-assisted circular fixation include the
ones mentioned above. However, the authors feel that the secondary
benefits are what can make hexapod-assisted circular fixation,
at times, superior to a static Ilizarov device or internal fixation.
Hexapod-assisted circular fixation will allow the surgeon to:
• Realign malaligned bony segments precisely
• Maintain foot and ankle height and length without
decreasing cubic bony contents via wedge resections
• Allow for concomitant management and gradual correction
of hindfoot and midfoot deformities
• Address large angular, translational, and rotational
deformities without significant risk of neurovascular compromise
• Convert to earlier weight bearing
• Manage soft-tissue defects
• Perform multi-stage operations that allow for delayed
definitive treatment in the presence of active bony or soft-tissue
infection
These factors should be considered when planning surgical
intervention for patients experiencing deformity secondary to CN.
Identifying which patients would benefit from the hexapod-assisted
correction is equally as important as the indications and benefits of
surgery. The authors recommend the following guidelines:
• Patients should have good overall bone stock in the midfoot
and hindfoot. Though midfoot and hindfoot Charcot joints can lead
to bone loss/dissolution, having large bony segments that have not
been ravaged by CN is important in reconstruction of “normal” pedal
architecture (Figure 1).
• If patients have subluxation of joint segments without
significant bone loss or fractures, the joints can be realigned precisely
utilizing the software programming (Figure 2).
• Midfoot “bayonet” deformity (Figure 1) is a common
deformity that lends itself to this method. In this correction, a “butt
joint” can be used to raise the lateral column and realign the pedal
arch.
• Large angular deformities may be present in multiple
planes (Figure 2).
These features can be difficult to address in the midfoot and
hindfoot without significant shortening of the limb. Hexapodassisted
circular fixation allows for gradual correction in all planes.
Important at risk soft-tissue and vascular structures can be protected
and accounted for during this correction.
Recent comparisons of internal and external fixation for
limb reconstruction and salvage has yielded promising results.
In 2012, a review of the literature by Dayton “et al”. [13]. showed
that while external fixation was used in cases with a higher degree
of complication, external fixation had greater odds of success over
internal fixation. Lee “et al”. [6] in 2016 showed via literature review
that external fixation resulted in decreased risk of amputation,
wound healing problems, deep infections, need for further surgery, and intraoperative and perioperative fracture when compared with
internal fixation. While more studies are needed, it is clear that
external fixation is a reliable choice for deformity correction in CN.
Additionally, advances in hexapod frames and improved software
have decreased the complexity previously associated with dynamic
framing options to address Charcot reconstruction.
Figure 1
Figure 1
Midfoot Charcot deformity. Equinus of the hindfoot and dorsal
subluxation of the midfoot onto the hindfoot creates a “bayonet” deformity.
This deformity can progress to rockerbottom foot type. Lack of bone loss/
dissolution serves as good indication for hexapod assisted correction.
Copyright 2017, Rubin Institute for Advanced Orthopedics, Sinai Hospital of
Baltimore.
Figure 2
Figure 2
Joint subluxation without fracture can be accurately re-aligned
with hexapod-assisted circular external fixation. Large angular deformity
can occur in multiple planes and create significant soft-tissue deformity that
needs to be addressed gradually. Acute correction will require large bony
resections that may not be desirable in certain circumstances.
Figure 3
Figure 3
Saltzman view provides a frontal plane relationship of the hindfoot
with respect to the long axis of the leg. Copyright 2017, Rubin Institute for
Advanced Orthopedics, Sinai Hospital of Baltimore.
Clinical Presentation
Upon clinical presentation of patients with CN, it is important to thoroughly assess both the deformity and the individual to determine if the patient can understand the demands associated with hexapodassisted external fixation. The presence of co-morbidities, control of HbA1c, social support system, vascular status, tobacco or recreational drug use, and nutritional status must be optimized in these candidates prior to any surgical intervention.
Radiographic Evaluation
When evaluating the deformity, plain radiographs and 3-D
weight bearing Computed Tomography (CT) scans are the senior
author’s (NAS) imaging modalities of choice. These imaging studies
allow complete understanding and quantification of sagittal, frontal,
and transverse planes as well as rotational deformities of the foot
and ankle. 3-D weight bearing CT scans provide a comprehensive
assessment of any fractures or dislocations present in the foot or
ankle. The surgeon can address them intraoperatively via fusions,
realignment, and/or osteotomy. Preoperative measurements allow
the surgeon to use hexapod software for pre-planning of length and
breadth of correction.
Plain film radiographs should include standard views of the foot
and ankle. The senior author (NAS) routinely obtains limb length
assessment films and Saltzman views. Erect full length standing AP
views radiographs are obtained that visualize the lower extremity
from the hip to the foot. This view can assist in planning potential
shortening and/or simultaneous limb lengthening that can occur
during treatment. Saltzman views provide frontal plane relationships
of the hindfoot, ankle, and lower leg (Figure 3) [14]. In hindfoot CN
cases, the varus and valgus relationships can be visualized accurately
on Saltzman views. Some hexapod software programs allow for
deformity planning and determination of proximal and distal
reference points prior to surgical intervention.
Case Studies
We present two patients who were selected for complex Charcot
reconstruction in the midfoot and ankle with a hexapod device. The
midfoot and hindfoot CN surgeries were performed by the senior
author (NAS).
Case 1: Hindfoot charcot deformity
A 62-year-old woman with type II diabetes presented with
longstanding right foot and ankle Charcot deformity. She had
experienced the deformity for more than 1 year after failure of
conservative treatment and bracing. She had a history of rheumatoid
arthritis, deep vein thrombosis with pulmonary embolism,
hypertension, and thyroid disorder. These medical issues were well
managed by her primary care physician. Her HbA1C was optimized
and within normal limits.
The patient had an obvious hindfoot and forefoot dislocation
with shortening on to the ankle joint in a valgus attitude (Figure 4).
Her foot and hindfoot were laterally displaced and subluxed with
respect to the long axis of the tibia, and soft-tissue thickening was
observed over the talar head. She had no history of open wounds,
but significant callus and soft-tissue redundancy were noted medially.
Her foot was not freely reducible and was locked in a valgus position
with respect to the ankle and leg.
A 3-D weight bearing CT scan was obtained as well as simulated
weight bearing plain film radiographs (standard foot and ankle views,
erect full length standing AP view, Saltzman view). The radiographs
revealed a 5.5-cm lateral displacement of the calcaneus with
approximately 7 cm of shortening of the calcaneus onto the ankle
joint (Figure 5). The hindfoot was in a 45-degree valgus deformity
with respect to the long axis of the tibia. A complete dislocation
through the subtalar joint without fractures of the ankle, talus, and
calcaneus was observed. No fractures, bony dissolution, acute osseous
destruction, or evidence of osteomyelitis were noted.
A two-stage external fixation surgical strategy was employed
to correct the deformity. The goal of the first stage was to distract
and realign the foot and subtler joint on the ankle via hexapod-assisted external fixation over the course of 3 weeks (Figure 6). The
second stage of the surgery converted the dynamic portion into a
static construct for focused fusions of the hindfoot and ankle. In the
postoperative period, the patient was allowed to be weight bearing
as tolerated with the assistance of the walker. In the postoperative
period, the patient had a relatively uneventful course. She did not
develop any pin-site infections; however, one pin had to be removed
for soft-tissue irritation. Once radiographic evidence of bony fusion
was noted, the external fixation device was removed. The patient was
converted to full weight bearing in a protective boot and will maintain
this boot for 1 year. After 1 year, she will be allowed to transfer to
regular extra depth diabetic therapeutic shoes.
Case 2: Midfoot charcot deformity
A 72-year-old man with type II diabetes presented with a recent
diagnosis of CN. The patient reported a progressively collapsing
medial arch with formation of a pre-ulcerative lesion on the midfoot.
No tissue breakdown was observed. After radiographic evaluation, a
midfoot Lisfranc Charcot deformity with collapse of the midfoot and
bayonetting of the forefoot on the hindfoot was apparent (Figure 7).
The patient was at risk for developing ulceration; therefore, a twostage
correction with hexapod-assisted external fixation was planned.
During the first stage, the procedures to correct equinus and apply
the hexapod were performed (Figure 8). The patient carried out the
strut adjustments over a course of 2 weeks and then returned to the
operating room for the second stage of treatment. During stage two,
the gradual correction frame was converted to static external fixation.
Multilevel focused joint fusions of the forefoot, midfoot, and hindfoot
were carried out. The ankle was spared. Radiographic healing was
noted approximately 10 weeks after application of the hexapod in
stage one, thus allowing frame removal (Figure 9).
Postoperative period
The postoperative protocol for each patient depends on the frame
construct and which stage of deformity correction the patient has
completed. The senior author (NAS) does not allow patients to bear
weight on the external fixator during the dynamic correction phase;
however, patients may begin gradual to full weight bearing with the
assistance of ambulation devices once they have entered the static
phase of the correction.
Though not necessary for all patients, many patients will
eventually require admittance to either an inpatient rehabilitation
or acute skilled nursing facility postoperatively for physical therapy
and/or occupational therapy. Strut adjustments are initiated once
skin incisions have healed (approximately 10 days). Pin care is based
on surgeon preference, and the senior author (NAS) allows patients
to shower after skin healing is noted. The external fixator remains in
place until signs of radiographic bony healing, which can be typically
3 to 4 months. Computed tomography scans can be helpful in
evaluating the fusion sites if hardware impedes accurate radiographic
evaluation of fusion sites. Protected weight bearing is carried out in
a boot or protective ankle-foot orthosis for up to 1 year. The patient
transitions to supportive diabetic shoe wear and then ankle-foot
orthoses. In both cases, it is important to protect the fusion site for the
lifetime of the correction with a custom-molded ankle-foot orthoses.
Complications
The most common complication associated with external fixator
assisted surgical intervention of CN is pin-site infection, occurring in
8.4% to 100% of the cases reported in the literature [15,16]. However,
most of these infections are superficial and treatable via a short course
of oral antibiotics and local wound care [17]. Rare complications
include deep-tissue infections, osteomyelitis, pin loosening, delayed
mobilization, hardware breakage or failure, non-tolerance of external
fixator device, loss of fixation, or nonunion [17,18]. Many of these
complications may result in the removal of pins or the frame entirely.
In the senior author’s (NAS) experience, localized pin-site infections
are the most common complication seen in this patient population.
To lower pin-site complication rates, the senior author educates
patients about pin-site care and advises patients to use chlorohexidine
sponges for localized pin-site care.
Figure 4
Figure 4
Clinical appearance of Charcot dislocation. A, Simulated
weightbearing of right foot. B, Axial appearance of the foot.
Figure 5
Figure 5
A, AP view of the ankle shows subtalar joint dislocation and angular
deformity. B, Lateral view shows significant shortening of the hindfoot on the
ankle.
Figure 6
Figure 6
A, Two-stage approach was utilized. During the first stage,
the gradual correction was used to create axial distraction of the limb. B,
Radiographic presentation 3 weeks after distraction. Appreciate the subtalar
joint and calcaneus distraction. C, Conversion to hindfoot fusion with minimal
bony loss.
Figure 7
Figure 7
Midfoot Charcot deformity with progressive collapse of pedal arch.
A, AP view radiograph of the foot B, Lateral view radiograph of the foot.
Figure 8
Figure 8
A, Acute equinus correction was maintained with a temporary
extra-articular fixation pin. B, Application of hexapod apparatus for gradual
correction of deformity.
Figure 9
Figure 9
A, Lateral view radiograph with external fixation construct in place.
After correction was achieved, it was maintained with intramedullary foot
fixation. B, Lateral view radiograph obtained after frame removal. Arch is
restored, and solid fusion is noted in the midfoot.
Discussion
Both cases illustrate examples of successful utilization of a
hexapod device. In case 1, the external fixator gradually distracted
the bony and soft-tissue structures that had adapted to a chronic
dislocation. The dorsal lateral dislocation of the calcaneus through
the subtalar joint was maintained in a non-reducible valgus position
due to the Achilles and peroneal tendon contracture. Axial distraction
provided enough stretch of the Achilles, peroneal and tarsal tunnel
contents to safely realign the bony elements of the subtalar joint.
Bony distraction past the fibular malleolus and talus facilitated
anatomic realignment of the hindfoot on the ankle. A key technical
tip during this procedure is to secure the talus in the mortise. This was
accomplished by placing non-tensioned crossing wires through the
talus and securing them to the proximal non-moving fixation block.
Not securing the talus can create varus or valgus rotation within the
mortise during large angular corrections. After successful alignment
is achieved in the second stage, accurate and adequate preparation of
the joint surfaces can be performed. The hexapod can be converted to
a joint compressive frame to achieve fusion of the hindfoot segments.
In case 2, the same principles of a staged operation were used.
Midfoot Charcot deformity poses similar challenges of soft-tissue
deformity and bony structures impingement, which maintain the foot
in a deformed, maligned position. In midfoot Charcot, the collapse of
the medial column in conjunction with lateral column subluxation
creates a radiographic presentation in which the forefoot “bayonets”
on the hindfoot (Figure 1). The Achilles tendon gains a mechanical
advantage with collapse and further maintains the hindfoot complex
in an equinus position. The forefoot dorsally displaces and locks over
the hindfoot. The locked position can be maintained by consolidating
fractured cuneiforms along with the extensor tendons and tibialis
anterior tendon. The peroneal tendons further create a transverse
plane deformity by acting on the forefoot.
The hexapod can address the hindfoot and midfoot/forefoot
deformity simultaneously by creating a “mitre” frame construct. This
complex construct acts as a double-level hexapod for independent
guided correction of the ankle/hindfoot and midfoot/forefoot.
Though an excellent method for correction, the senior author (NAS)
recommends simplifying the construct in Charcot joint patients
by utilizing a “butt” frame design. The “butt” frame construct can
decrease the complexity of the correction for the surgeon. The
hindfoot equinus deformity, with this method, is addressed acutely
during the first stage of correction. In the first stage, the equinus
contracture of the Achilles tendon can be accomplished by surgeonpreferred
method of Achilles lengthening. Once the calcaneal pitch is
restored, it is temporarily stabilized by placement of an extra-articular
pin from the calcaneus into the posterior tibia (Figure 8a). This
simplifies the correction by letting the surgeon focus on returning the
malaligned midfoot and forefoot to a normal hindfoot. A technical tip
is to place “stirrup” wires across the area of distraction and connect
them to the distal ring. If needed, an open or percutaneous midfoot
osteotomy should be performed. The need for osteotomy is based on
the degree of bony consolidation. A consolidated midfoot deformity
usually requires osteotomy. Bony dissolution or non-united midfoot
fractures, generally, will not require osteotomy. Prior to any angular
correction or translation, the surgeon must obtain axial distraction of
the forefoot to decompress the bony and soft-tissue structures of the
midfoot. Not allowing for adequate distraction will make it difficult
to accurately re-align the lateral Meary’s angle or allow the midfoot
cuneiforms to be exposed from the dorsal dislocated foot. Once
alignment and distraction is achieved, the goal of the second stage
should be to maintain correction by obtaining arthrodesis from the
hindfoot to the forefoot. This requires adequate preparation of the
articular surfaces of the medial and lateral column bony structures.
Compression of the arthrodesis complex can be done utilizing the
frame but is difficult to execute. The author recommends placement
of axial wires or intramedullary placement of wide diameter screws
through the medial and lateral columns of the foot (Figure 9a/9b).
The hexapod frame can be converted to a static device to protect the
arthrodesis site during the healing period.
Summary
CN continues to remain a devastating, limb-threatening disease.
Management can be complicated by complex medical and social
challenges. Correction of CN is well documented by techniques for
bony deformity reconstruction. Correction via external fixation has
been shown to be an appropriate method for surgical stabilization of
an affected limb. When using a multiplanar hexapod-assisted external
fixator system, the authors have the following recommendations:
• Knowledge of the Ilizarov technique is critical to successful
application of any external fixator. The goal of hexapod-assisted
surgery is to obtain the correction in two stages: the first stage consists
of gradual correction and the second stage is the conversion of the
dynamic frame to a static frame to maintain the correction.
• Hexapod-assisted correction requires the use of a software
program. Becoming familiar with entering the deformity parameters
into the software program will ensure a successful treatment outcome
with minimal adjustments in the perioperative period. Continued
medical education and mock computer simulations can assist the
novice surgeon in learning various systems.
• Identifying appropriate candidates for hexapod application,
as mentioned earlier, is critical to achieving an accurate outcome.
Candidates should have the following features/requirements:
• Good bone stock with minimal bone loss
• Individuals with joint subluxation without fractures
• Large angular deformity
• Concern for soft-tissue quality
• Need to maintain limb and foot length
The surgeon must remember that the goals of Charcot deformity
correction are to create a stable, braceable foot that allows for community ambulation to accomplish most activities of daily living
[3,19]. Properly executed hexapod-assisted Charcot deformity
correction is a powerful and valuable tool in the foot and ankle
surgeon’s armamentarium in achieving these goals.
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